Wednesday, March 21, 2018

Shallow Water ASW Story

“Torpedo in the water!”

The abrupt announcement from Sonar Control caused the usual instant flood of adrenaline in the combat watchstanders aboard the USS Morton.  Each silently and guiltily prayed that someone else in the ASW squadron would be the target.  The men collectively held their breath for a moment as Sonar rattled off the distance, bearing, and course of the torpedo.

“It’s headed for Fluckey.”

After a split second’s hesitation for those who weren’t the target to silently thank the gods of ASW, the group’s ships reacted and began the envelopment. 

Tactics for this kind of shallow water ASW operation had been learned or, in many cases, relearned, the hard way and the price of that learning had been blood and ships.  Now, though, the three other ships of the group - the Morton, O’Kane, and Gilmore (somewhat ironically, the Morton class ASW corvettes had been named for famous WWII submarine commanders) – began their well practiced envelopment maneuver.  What had previously been a four-ship, line abreast, hunting formation now peeled off in different directions to encircle the point where the torpedo had originated and which contained the enemy submarine.  The fourth ship, the Fluckey, which now had a torpedo pursuing it, had turned away to run at maximum speed.  That was how these envelopments worked.  The unlucky targeted ship turned and ran while the remaining three ships attempted to surround the submarine and fix it in the center of a triangle.

As Fluckey turned to begin her run from the torpedo, she also launched one of her Mk54 lightweight ASW torpedoes back down the bearing of the incoming torpedo.  This was intended to distract the sub while the three remaining ships began their envelopment and to, hopefully, cause the sub to break any control wires to the incoming torpedo.  There was also the off chance that the ASW torpedo would actually hit the submarine.  It happened occasionally, but not often.

As the three encircling vessels began to reach their assigned points of the triangle they shifted from their hunting mode of randomly alternating between active sonar and passive listening to continuous active searching.  It was imperative to find and fix the sub’s location and begin attacking before it could settle on its next target. 

By now, the torpedo chasing Fluckey was entering its terminal approach and it was apparent that Fluckey was not going to evade the incoming torpedo.  This was not unusual as the fleeing vessel in this scenario typically only managed to evade the torpedo about half the time.  This did not, however, mean that Fluckey was doomed.  Aboard the fleeing ship, the ASW mortar, an adaptation of the old Russian RBU-6000, trained back down the vessel’s wake as the ship, itself, abruptly slowed and turned to allow the ship’s hull mounted sonar to get a precise targeting fix on the incoming torpedo.  The data was quickly transferred to the mortar which twitched slightly to its final firing position and a volley of six compact ASW rocket propelled depth charges arced up and out to fall in a pattern around the torpedo’s predicted location.  The charges quickly sank a dozen feet or so and exploded as one on a timed fuze.  As often happened, the incoming torpedo was violently deflected off its path and, by the time it settled back down it’s direction had changed sufficiently that the small on-board sonar in its nose, with a very small and narrow field of view, was unable to reacquire the Fluckey and the torpedo headed off in a safe direction to eventually expend its fuel and sink to the bottom.

This tactic required perfect timing since slowing and turning the fleeing ship ensured that there would only be one, or at most two, attempts to deflect or destroy the incoming torpedo.  If the attempt failed, as it did about 20% of the time, the fleeing ship was almost certain to be sunk.  In the cold, hard math of combat, this was acceptable as the ASW corvettes were cheap and easily replaced.  Understandably, the crews did not share that feeling.

Breathing a sigh of relief, Fluckey cautiously turned back toward her sisters to eventually rejoin the hunt.

Meanwhile, as the rest of the group continued their search, the ships acted as gatekeepers, preventing the sub from slipping out of the triangle no matter which way it turned.  They slowly began constricting the triangle and herding the submarine towards the center.

Depending on the submarine’s behavior, this search could take many hours.  Passive sonar had proven ineffective in shallow water due to the ambient noise overwhelming and masking any target noise.  Non-nuclear subs were notoriously quiet and hard to find in shallow water.  Ultimately, though, active sonar had proven effective.  The “quietness” of a sub didn’t matter when active sonar was applied.  It was usually just a matter of time before the sub was localized. 

Of course, the drawback to active sonar was that it provided the submarine with a precise fix on the hunting ship’s positions and it was not uncommon for the submarine to fire back at its attackers.  O’Kane had encountered this a few weeks previously and had saved itself by turning directly into the torpedo and closing at full speed.  The ship had managed to get inside the torpedo’s safety range limit and then taken advantage of the proximity to the sub to launch a full volley of contact fuzed mortar charges which had achieved a single hit that damaged the sub, forcing it to the surface where the group’s 76 mm guns quickly ended the encounter.

The three searching ships continuously shared their data to assemble a composite tactical picture and triangulate the submarine’s position.  Aboard the Morton, the group ASW Commander decided that the tactical picture was solid enough for an attack.  Gilmore was currently in the best position and he transmitted the order for a short range ASROC launch.  Gilmore’s launcher trained out and the rocket fired.  The torpedo splashed down on top of the sub’s position and began its search pattern.  The submarine immediately went to full speed and turned away from the torpedo.  Unfortunately for the sub, it turned towards O’Kane which quickly launched a Mk54 torpedo to meet it.  The sub was now sandwiched between two searching torpedoes and running out of options.  This was exactly why the corvettes were always deployed in squadrons.  Numbers were the key to the corvette’s success. 

A final, desperate turn by the sub resulted in it heading towards Morton who also launched a Mk54.  At this point, with three torpedoes surrounding it, the sub’s fate was sealed.  O’Kane’s torpedo made the first hit and Gilmore’s ASROC torpedo quickly finished the sub.


This story is an exploration of corvette anti-submarine warfare tactics.  The tactics are based on a compilation and analysis of several papers and articles dealing with ASW, sonar characteristics, shallow water acoustic characteristics, and ASW weapons.  An example paper is listed below (1).

Notably, aviation assets are not involved.  I’ve described the force structure and CONOPS into which corvettes fit and the rationale for not including helos on the ships.  This scenario describes a set of tactics that could make that option viable.

This is a single scenario.  In the real world, there might well be other assets, both surface and aerial, that could be called upon for assistance.  It is not intended that this scenario and the ASW corvette be considered the only means or even the best means of conducting anti-submarine warfare.  It is simply one means using one type of platform and is intended to show how a low end platform can, with proper tactics, perform effective ASW without the benefit of helos.

To summarize, the following tactical elements were demonstrated:

  • Line abreast sweep
  • Envelopment – contacting vessel runs while others envelop
  • ASW hunting in squadrons
  • Short range active sonar
  • Continuous active sonar
  • Triangulation from multiple ships
  • RBU / Hedgehog as anti-sub weapon
  • Sail into short range torpedo contact to get inside torpedo safety limits
  • RBU as anti-torpedo tactic

I hope you enjoyed the story format!


(1)Naval Postgraduate School, “Passive and Active Sonar Prosecution of Diesel Submarines by Nuclear Submarines”, Erik J. Nelson, March 2008


  1. Totally agree, all "proper" navy's should have ASW corvettes / small Frigates. Trouble is they are not "sexy" enough for the top brass / politicians. Bit like MCM, which is why every time there is a cut in The Royal Navy MCM comes of badly even though it is (or was)one of our "premier league" capabilities (off topic sorry). End of rant.

  2. Replies
    1. Thanks. Hopefully, this was a more entertaining way to convey the concept as opposed to a dry recitation of bullet points. Plus, I enjoy a bit of fictional writing.

    2. ASW is near and dear to my heart, sometimes a fictional account can describe things way better than a PPT presentation. Much less painful as well!

    3. Have you had some ASW experience or exposure that you'd care to share? We too often ignore the lessons that the past can offer to the future. Maybe there's lessons you've learned that you see as applicable to today's setting?

    4. I'm just an old Air Force guy with an interest in naval combat. (Four kids are/were all Navy. Hence the interest.)

  3. How close would the corvettes need to be to each other for this kind of tactic to work, are we talking about less than 2nm or something like 5nm or even more ?

    1. Gotta hand it to you, you've jumped right to the key question! Short answer: I don't know. Longer answer: the spacing would be close/far enough to provide a bit of overlap of the active sonar ranges of the ships. I don't have access to real world active sonar range data so I simply don't know. This part would have to be left to the real world practitioners to determine. My guess is a spacing of around 5 miles between ships, so you hit it about right! For four ships, that provides a coverage sweep lane 25 miles wide. That ought to be useful in shallow water ASW. Of course, the spacing would be adjustable as acoustic conditions change.

    2. While I understand that your story is a snapshot, there still might be some problems with the spacing.

      With a spacing of 5 miles and three corvettes I would think the sub would have to accidentally wander into the middle of them or close to them. Usually that luck is on the sub's side.

      The Navy suspected and later confirmed the value of those helos in ASW. Without them, ASW is a fair fight at best with most of the physics on the side of the sub. With helo's it is still a disadvantage for the ship, but the helo can use range and speed to throw up a kill box around the sub. Basically they may have the advantage but with airborne assets it is closer to a suicide mission than without helo's. Without airborne assets the sub has a good chance to escape with three corvettes killed. While the Navy does a lot of stupid stuff, just like every government, sometimes they use some smarts. Putting helo's on surface ships was done for a very real reason. It is a game changer once the sub is found. Without it, the Navy my quickly loose the war of attrition. It is that important.

      With close to shore, littoral corvettes the helo's can assist from shore and then land to refuel on the corvette. i.e. no hanger and less support needed. But still a necessity for ASW wins.

    3. You're missing two very important points:

      1. I have no idea what spacing would be appropriate. I've offered a guess but someone with knowledge of actual shallow water sonar performance would have to determine the optimum spacing. Actually, I've read many reports about shallow water acoustics, sonar performance, and shallow water ASW tactics so my guess is actually a semi-informed guess. Doesn't mean it's right but it has at least some basis.

      If you have such knowledge, please share with us. Otherwise, you're guessing just like I am. Do you have some relevant knowledge to make a statement about spacing or are you just disagreeing based on nothing?

      2. The Navy has determined that naval aviation is valuable and yet we don't put thousand foot carrier flight decks on every ship. Why is that? The advantages of a full air wing are quite obvious. Should I go ahead and describe all the benefits of an air wing? Or, should I simply note that we can't afford to put full carrier flight decks on every ship we build no matter how good advantageous an air wing is? The same applies to helos and ASW. Have I ever stated that a helo is not useful in ASW? No, I have not. What I have stated is that we can't afford to build the numbers of ships we need if we insist on trying to put every useful capability on every ship. An ASW corvette is a small, cheap ASW platform that offers advantages around the periphery of a war and won't break the bank. Adding two helos to a corvette makes it a frigate and we're already seeing that the Navy's new frigate is going to cost around $1.5B. We can't afford plentiful $1.5B frigates to provide the numbers we need and do we really want to risk $1.5B ships playing tag with submarines?

      I'm going to say it one last time. NO ONE IS SAYING THAT HELOS ARE NOT USEFUL IN ASW. We simply can't afford it. It really is that simple.

    4. "While I understand that your story is a snapshot"

      No. You're also failing to understand that the story is NOT a combat simulation. It's a simple exploration of possible small vessel, non-helo, ASW tactics. Nothing more, nothing less.

    5. My point is that if a person who understands the nature of the threat of say an older Russian torpedo then the separation of the ships will need to be father away to keep all three corvettes from being engaged at once. Mixing that data with speed of an average diesel sub and average corvette and you can see where it might not work all that well if at all.

      This separation is important because it can invalidate the corvettes ability to stalk and triangulate the sub even if they all survive.

      Those two basic ideas make the best way (and sometimes the only way) to stalk subs, get in front of them and put them in a kill box is to use air assets such as helo's to make the triangulation. Something that could take a day now takes an hour.

    6. "My point is that if a person who understands the nature of the threat"

      I say this gently ... You are not that person. If you're going to continue to contest this then you need to come up to speed on shallow water acoustical conditions, sound propagation in shallow water, sonar performance in shallow water, shallow water ASW tactics, etc. The littoral waters are horrible for active or passive sonar. A submarine has no magical powers that an ASW corvette doesn't have. The use of active sonar is not an instant death warrant. Active sonar will provide a bearing, maybe. The channeling of sound, echoing, distortion, and background in shallow water makes tracking even active sonar sources at a distance difficult.

      There are not a lot of papers out there on the subject but there are enough to assemble a coherent understanding. I have searched out those papers, studied them, and come to an understanding, at least as well as can be had without access to actual performance reports. I encourage you to do the same. Your concerns are understandable but only partially correct.

      Finally, understand that while I have put some effort into understanding this subject, I make no claim to be an expert on shallow water ASW. Nor, sadly, is the Navy! Perhaps my vision is totally unworkable. If so, someone will have to come up with new tactics. But, until I meet someone who has studied this more than I have or has real world experience, I'll stick with what I've offered.

      Your welcome to disagree but do so with data. Read the various reports and cite data that proves me wrong, if there is any. I suspect you're attempting to apply open ocean ASW concepts to shallow water and it just doesn't work. It's a completely different game.

    7. Hmmm....basic triangulation of 1940's requires a triangle. So we will stay in the past for now. If I told you I could triple the speed of your corvettes I don't think you would require me to cite a wiki to understand that you could triangulate faster.

      Would I need a wiki citation for you to understand that once you decide to fire a torpedo on a ship or sub that in some circumstances having a 100 mile ranged torpedo might be better than a 6 mile ranged torpedo?

      Those two facts above is what Helo ASW brings to the table. The speed, distance and ability to act as a force multiplier makes helo's the way to go. It saves money and lives. That was even true in 1940's(not done until after the war due to a variety of factors such as army/navy rivalry and weight of early sonars) and it's true now.

      For you to suggest that the Navy can't afford Helo's for ASW suggest to me that you have not matured your thinking much beyond WWII tactics.

      Now let's move to the new century in ASW. The tech revolution of the late 80's in computing (processor speed, fast Fourier Transforms, Synthetic aperture radar and beamforming just to name a few) that allowed a UHF search radar to increasingly be used as fire control radar at at every greater distances using the same transmitter power (think E2-C directing missiles to ships now where that would have been a joke in the 80's) is the same Fourier Transform, moved to Fractional Fourier, Beamforming, Synthetic aperture radar that has from 1998 to late 2000's matured and continues to transform ASW.

      Even more impressive is that most of this revolution directly translates to the littorals. Beamforming to reduce side lobe/reverberation and increase range for the same transmit power.

      What did this revolution do? One article below talks about a 3 to 7 times increase in the detection range of the dipping sonar the Navy uses in it's helos.

      The reality is that these transformations have increased the detection distances for active sonar in the 2000's and is transforming passive detection in the same way today. Thus have made wartime attack distances longer. i.e. spacing increase between ships to avoid both being engaged at once.

      What is not in the literature but is just a fact of the math, the synthetic radar/sonar that allows me to make short ranged pictures of the ocean bottom allows me to pic out the target at larger distances from the clutter. Synthetic radar was initially all about increasing detection at range not about short range pictures of the sea floor.

      Lastly, what this signal processing does is allow me to range the sub or ship faster, more accurately as well as get a bearing. What was a range guess before 1998 would not allow me to fire a torpedo without more time to triangulate. It is now much more accurate. That translates into into not needing three corvettes. It translates into less sonobuoys needed, and a more direct dropping of the torpedo. It means ASW warfare has changed almost completely. From time of the kill chain to standoff distance.

      In a word of classified data how can you understand this. Educate yourself on the basics of Fourier Transform, beamforming, etc. No one is going to admit that but they will admit that ranges are increasing due to the revolution of the last 20 years.

      What is coming in the future? People talk about placing UUV's on the end of the MFTA so that they can computer control the shape of the array. Beam forming of the actual array is genius (think AESA sonar).

  4. A few notes taken from the MK 54 LWT DOT&E 2017 report, "little data were obtained to assess MK 54 performance in challenging, operationally realistic scenarios // Conduct operationally realistic mobile target set-to-hit testing and minimize test limitations // Navy has not developed a mobile target surrogate for set-to-hit testing //Improve the MK 54’s effective target search and detection capability// Improve the target detection, localization, and track performance of ship and aircraft // MK 54 should be able to effectively search the area defined by typical fire control solution accuracy.

    The DOT&E report on Surface Ship Torpedo Defense (SSTD) System: Torpedo Warning System (TWS) and Countermeasure Anti‑Torpedo (CAT) for the CVNs, similar conclusions to Mk 54, looks promising, Navy currently underfunding.

    Mk 54 and SSTD both need higher priority/funding, not sure of cost of SSTD but would appear that should be adapted more widely in fleet when fully developed.

    Targeting new generation quiet subs with their anechoic tiles not easy, said in Falklands the Argentine subs hid on bottom amongst wreaks of old sunken whalers.

    CNO what level of effectiveness do you think your scenario is with current TRL of the Mk 54, remembering problems with the WWII HWT.

    1. Given the Navy's failure to test any torpedo under realistic use conditions, I have no faith that the torpedoes will work well. No, let me restate that. I have absolute certainty that the torpedoes will not work well.

      That's one of the reasons why I heavily favor the inclusion of a RBU/Hedgehog type weapon on ASW ships. I think we'll have a lot more close up encounters than we anticipate both because our detection capability in shallow water won't be as good as we hope and because our torpedoes will not be as effective as we hope, thus allowing the sub and ASW ship to get closer to each other than hoped.

      Also, you noted the theorized tactic of RBU "bombing" of an incoming torpedo. Supposedly, this is one of the capabilities the Russians claim for the RBU. We need some kind of anti-torpedo defense and the SSTD is not yet ready.

  5. Great story CNO! And it also brings home the point that sailors really need much much more than basic seamanship skills to be effective in combat (and avoid commercial shipping). Everyone who even has a slim chance at taking over the controls should be practicing precision maneuvering. And thats not even mentioning the overall crew and ship-to-ship coordination.

    1. "sailors really need much much more than basic seamanship skills to be effective in combat"

      You make a great point! Basic seamanship is, well, basic. Combat seamanship is something else again. I recall reading about the early WWII carrier captains who, while evading bomb and torpedo attacks, operated their carriers like destroyers with violent, high speed maneuvers never seen in peacetime. Left unstated was how they developed those ship handling skills.

      Certainly, we don't allow today's carrier captains to practice violet evasive maneuvers so one can't help but wonder how they'll handle their ships in combat?

      Great comment.

    2. I can't speak for, "today" but in the late 80's/early 90's we used to play, "office chair".
      On workups we would fly out to the ship to get it read for the squadron. It was a requirement to put the ship through it's paces.

      While the captain went through evasive maneuvers we would sit in the AT shop on the forward starboard bow under cat 1 in a rolling office chair and wear our helmets.

      I very much remember laughing my ass off while having my feet on the wall which was around 45 degrees. My butt would lift off the chair for a second or two before we would swing back around.
      When one is young and bored that counts as fun.

      Even to this day it is amazing to think just what the Nimitz could do when it was needed.

      Again I have no idea if that is still part of the normal workups.

  6. You have my full endorsement. The key feature is that you are using the anti-sub corvettes in groups. Today we often get stuck in a one on one mentality. We could likely build, crew, and maintain a few of these corvettes for the same cost as one of our SSN's. Make it a design that small non-military shipyards could build during wartime. During peace time, maintain enough corvette squads to develop tactics and conduct training.
    How about basing the design on a current civilian ship that could be re-outfitted for ASW during war-time?

    1. "How about basing the design on a current civilian ship that could be re-outfitted for ASW during war-time?"

      I have no problem with that! The only problem I could foresee is that you'd like a ASW corvette to be acoustically isolated and that would an unlikely feature in a civilian ship.

      Commercial ships that are pre-adapted to future military use is a staple of Chinese commercial shipbuilding and a practice that we should emulate.

  7. "That's one of the reasons why I heavily favor the inclusion of a RBU/Hedgehog type weapon on ASW ships"

    The only some kinda modern western system that is a close analog to the RBU that came first to mind is the 375mm Bofors depth charge launcher

    1. And this

    2. You probably already know, but the latest version of the RBU, the RPK-8, features a depth "rocket" with a homing capability (130 m search range). They claim up to a 80% probability of hit. It would make a very nice ASW weapon for a small ASW corvette.

    3. Ive been wondering, how the USN can achieve similar capability for minimum time and money.
      The first thing that came up is to just simply make a "cluster " warhead filled with dept bomblets for the VL-ASROC.

    4. Russia is desperate for cash. Why don't we just buy a system from them and reverse engineer it like the Chinese do?

    5. maybe because it seems logical, and you don't have major US defense contractors involved ( witch could build a similar system at a lot more expensive price) besides the "patriotic made in US" brigade would scream :D

  8. What if the sub fires at all four ships simultaneously? Do they all run? Seems like an easy way for the sub to break contact.

    1. Especially if he has Torpedoes that home on active sonar

    2. "Seems like an easy way for the sub to break contact."

      You get that these things don't happen in isolation, right? There would likely be additional assets, including aviation, that would be called in on first contact. No sub is going to want to announce its location by wasting torpedoes on small ASW corvettes that can be replaced easier than the sub can. Small size conveys a degree of immunity.

      Giving away its position leads to a mission kill if not an actual kill in a realistic combat environment. It's one thing to fire on a carrier and another to waste torpedoes on a tiny corvette.

      It's also quite likely that the ASW vessels would all launch ASROC torpedoes at the sub as soon as it announced its location with multiple torpedo shots. The ASROCs would arrive at the sub long before the sub's torpedoes reached the ASW vessels. In this scenario, for the sub to risk four ASROCs dropped on its location for the highly questionable gain of sunk corvettes suggests that the sub would be unlikely to attack unless detected and under attack itself.

      You need to think these scenarios through from a tactical combat perspective.

    3. "Especially if he has Torpedoes that home on active sonar"

      Do you understand that if a sub fires on a ASW corvette, the sub has already lost the battle? Several things can happen, all of them bad for the sub. Having given away its location, here's what can happen.

      -The corvette evades or counters the sub's torpedo and now the sub is the center of a hunt that likely ends in its destruction.

      -The sub sinks the corvette but is sunk in return. Remember, the corvette has ASROC which will arrive first and has active sonar.

      -The sub survives the encounter but a succession of other assets are called in, including aerial, and the sub is ultimately sunk - a win for the ASW side even if it costs a corvette.

      -The sub somehow survives the initial encounter and all the subsequent ones but in the course of doing so is pinned down for a protracted period and/or forced away from whatever its primary goal was - a mission kill against the sub.

      The only positive outcome is that the sub sinks the corvette, evades all subsequent searches and attacks, and is still able to execute its main mission, whatever that was. This seems are and away the least likely outcome.

      You need to think these scenarios through from an operational and tactical combat perspective.

    4. Ok, like you described above :

      " the ships acted as gatekeepers, preventing the sub from slipping out of the triangle no matter which way it turned. They slowly began constricting the triangle and herding the submarine towards the center."

      What the hell, is that sub skipper retarded or what, He has three Vessels closing on him with active sonar.. the knot around his neck is tightening ( obviously shallow water and he can not dive deep ) .. chances of escape are slim..
      What to do then - fire at will and try to escape at maximum speed deploying decoys.
      He knows he is gonna get hit anyway better fire first ans seize the initiative.

    5. "Notably, aviation assets are not involved."

      So now there are blue aviation assets?

      The first contact may be detecting inbound torpedoes. If the corvettes are pinging, the sub will see the corvettes well before the ships see the sub. If the sub doesn't feel it can evade, it can fire torpedoes outside of ASROC range and outside of likely detection range. Torpedo launches aren't that loud.

      With wire-guided torpedoes, the sub could fire them on one bearing and then turn them later, so it looks like they came from somewhere else. They can also start slower, and quieter and throttle up later.

      If the choice is getting cornered and destroyed by ASW corvettes or firing on them, any sub captain worth his salt will choose the later.

      I'd much rather send a group of active pinging MDUSVs out ahead of the manned vessels. Let them eat the torpedo counter-shots while the manned vessels deployed helicopters to pounce on and destroy the sub.

    6. "What to do then - fire at will and try to escape at maximum speed deploying decoys."

      Perhaps a modification to the tactic is to fire an ASROC from each ship at first contact and keep the sub too busy to develop a firing solution.

    7. "So now there are blue aviation assets?"

      I know you read a least a little bit of the post because you correctly quoted me:

      "Notably, aviation assets are not involved."

      So, you're either looking for an argument for its own sake or you didn't read your own sentence.

      You also failed to note the tactic of alternating passive/active searching until a threat is discovered.

      I also urge you to read up on shallow water acoustic conditions and active/passive sonar performance. You might start with the link I provided.

      If you'd like to discuss shallow water ASW tactics, that would be great but I'm not going to engage in a contrived argument about a story whose only purpose was to illustrate some possible small craft ASW tactics.

      When squadrons of fully autonomous unmanned ASW vessels become available, I'll write about those. Until then, we'll stick to assets that are more realistic.

      Consider your next comment carefully and be sure that it contributes something to the discussion. If not, I'll delete it.

    8. You don't need fully autonomous unmanned vessels for this.

      Instead of four ASW corvettes, trade one corvette for nine MDUSVs. Each ASW corvette then locally controls three MDUSVs via line-of-sight datalinks. They can share sonar pictures over the same datalinks.

      The MDUSVs assume a line-abreast formation ahead of the corvettes, and are the primary active sensors. The corvettes are strictly passive, listening in multi-static mode to MDUSV active pings.

      Since the spacing is tight (5nm), the MDUSVs don't need big, powerful sonars. Presumably Raython's MS3 would work just fine.

      The swath width for the full squadron would be ~50nm, twice that of just ASW corvettes alone. Plus, with 12 assets, a single sub can't kill all of them in one torpedo salvo. And he probably won't even hear the corvettes.

      MDUSVs could have ASW mortars or torpedo launchers for direct attacks, or let the corvettes handle it.

      Ideally the task force has a set of helicopters to quickly investigate and localize contacts, but they would have to come from somewhere else.

  9. Well, if we are talking ASW vessels i first think that if the USN should adapt a new design obviously it has to be oceangoing, that means something in the size of a small frigate at least.
    That of course has ts benefits that you can put more systems and weapons in it.

    1. "Well, if we are talking ASW vessels i first think that if the USN should adapt a new design obviously it has to be oceangoing"

      No, we're not talking ASW vessels, we're talking ASW corvettes and corvettes ARE oceangoing so that doesn't require something the size of a frigate. For example, Flower class corvettes conducted open ocean escort duties throughout WWII.

  10. Here's a video from our last submarine a Romeo class, just in case you want to see what a simulated torpedo attack looks like

    From 15:53 min

  11. I like the story format a great deal. It made the thrust of your thoughts very clear.

    1. Glad you enjoyed it. It makes a nice change of pace for me, on occasion.

  12. I'll stay away from the black shoe ASW talk.. Hot ASW warfare without AIR is like unprotected sex...

    IMO, the best weapon for shallow water ASW attack is the 500Lb air launched "depth bomb" deployed from fixed wing aircraft.. Doubtful they are still in use today....We only have a few remaining ASW capable P-3s (~40) and the P-8.


    1. As you know, we don't always get to choose the who/what/where/when of combat. We can't always assemble the exact right assets. Sometimes combat is thrust upon us and we have to make do with what we have on hand.

      We'll need low end escorts and patrol vessels like corvettes so it would be wise to ensure that they have at least some minimal capability to perform ASW and, with proper tactics, possibly even succeed.

    2. Of course sub hunting aircraft are the ideal. Back 50 years ago we had CVS aircraft carriers dedicated to hunting subs, but that's a lot of resources for a single mission. Worth the cost of stopping a Soviet SSBN, especially if it has nuclear missiles. Protecting supply convoys would be a likely mission for a ASW corvette group. It would be nice to have a CVS and air wing for every convoy and battle group, but not practical.

    3. "Of course sub hunting aircraft are the ideal."

      Of course they are. I've never said otherwise. Some people think that if I suggest, say, an ASW corvette that I'm also saying that no other ASW asset is needed. That's ridiculous.

      The reality in war is that there will be peripheral areas of conflict that don't justify our best surface, sub, and aerial ASW assets continuously operating in them. For those areas, we'll need cheaper, more plentiful, less capable assets. Especially in a peer war, we're going to find that our ability to operate aerial ASW assets like the P-8 or helos is severely limited - they're going to be shot down! We're going to need other assets to help out, such as an ASW corvette.

      Too many people (not you - I'm using your comment to make a point) seem to think that the only option is the gold-plated, gazillion dollar, do-everything asset and that anything less is not useful. Again, ridiculous. War isn't all ultra-high end assets. In fact, most of war involves the mundane assets that the U.S. seems to want no part of - like artillery, MCM vessels, mine layers, logistics ships, etc.

      I beg your indulgence for letting me use your comment to make a point.

      By the way, we need to bring back ASW carriers, as you mention! But no, those aren't flashy enough. We only want to build Fords class carriers.

  13. I don't quite see why the sub wouldn't engage the other corvettes as they move at high speed (and thus loudly) with either torpedoes or missiles.
    An E/O periscope can be raised, create a 360° panorama recording and disappear - all within a few seconds.
    Then the crew has a minute or two to identify the ships, estimate their distance, create firing solutions - all before a single corvette would have become fast and loud. The possible detection by radar would likely be considered a false alarm until a munition gets detected inbound.

    A counter-tactic to the described corvette pack tactic would be to deploy a couple electric torpedoes as mines, launch one silent electric torpedo from rather long distance, let it become faster (and detected) about where the deployed mines are, then watch the corvettes rush into the general area of the torpedo-minefield.

    Another counter-tactic would be to launch a silent electric torpedo, let it approach from a different angle than the sub's location (not all that difficult if the course of the corvette pack is at least somewhat predictable, as it would be in case of a coastal convoy).

    Finally, I'd like to remark that low frequency sonars have shown effective ranges vastly in excess of ASROC range against moving SSKs in shallow waters. The tracking of movement is useful for telling actual subs from false contacts.

    Ranges such as 5 nm or less are typical of mid and high frequency sonars. A ship-mounted or -towed LFAS puts is to long range ASW what AMRAAM is to BVR fighter combat: It leads into a different paradigm.

    1. "I don't quite see why the sub wouldn't engage the other corvettes as they move at high speed (and thus loudly) with either torpedoes or missiles."

      You read the post carefully, right? You noticed the part about the searching ships using combined passive/active searching to make it difficult for a sub to get a target solution? You also noticed the part where a targeted ship would immediately fire back at the sub? So, that minimizes the chance of a sub calmly developing target solutions and firing at every ship in a 25 mile radius.

      You also need to educate yourself about the realities of shallow water acoustics and passive/active sonar performance. The use of active sonar by searching ships does not grant a sub an instant, 100% accurate target lock.

      To put it delicately, your view of submarine/ASW combat is simplistic. You really need to study the underlying foundational reports about shallow water acoustics and sonar performance.

      Finally, the other side gets to develop tactics, too. Sometimes those tactics might even work! When that happens, we'll adjust. And then they'll adjust. And then...

      Recall that the point of the post was not to debate the minutiae of tactics but to demonstrate that small, cheap, ASW vessels could function without helos.

    2. Sorry, to get a targeting solution is not THAT difficult, particularly not when the enemies are moving quickly to envelop a position before that vague position guesstimate is utterly obsolete.

      I didn't write about "25 mile", so I sense a bit strawman fire smell here. Doubly so because of I didn't write "100%" either.

      "Recall that the point of the post was not to debate the minutiae of tactics but to demonstrate that small, cheap, ASW vessels could function without helos."

      Well, you missed that point because you're far from making it. You seem to depend on the assumption that the sub commander is cowered and waiting for his death after launching a SINGLE munition.

      The entire scenario falls apart if he launches four munitions right away instead.

      It also falls apart if one accepts that three moving corvettes with alternating active sonar use could be targeted by a submarine.

      It also falls apart if one assumes that heavyweight torpedoes or sub-launched anti-ship missiles have a good probability of hit and ASROC hasn't.

      It also falls apart if one pays attention to my mine trap scenario.

      It also falls apart if one assumes that a torpedo would not be detected until really, really close (remember, sonar issues in shallow waters et cetera!).

      It also falls apart if one assumes that a submarine can engage cargo ships (a real target that those four corvettes may be trying to protect) may be targeted and engaged by a submarine from 30+ nmi distance using missiles or LWL-connected torpedoes.

      It also falls apart if those "small, cheap ASW assets" are not survivable against a submarine's attacks because of cheap equipment.

      So essentially that point is novel-grade fiction so far.

      Finally, even if all these points were resolved in favour of corvettes, there would still be the question of cost efficiency in comparison to land-based ASW helos, attempts to secure a coastal lane with ASW mines et cetera.

  14. CNO, an idea for you next tale like this .

    Can you next time write about submarine vs submarine combat ?
    That would be interesting, for example a Seawolf SSN on a reconnaissance mission is stalked and jumped by a few chineese modern SSK's

    1. I'll take that under advisement. Submarines are the hardest to write about because they are the least publicized and documented in terms of performance specs. Without semi-accurate performance specs, writing becomes are more speculative than I like. But, the idea is appealing and I'll give it some serious thought.

      The other consideration is that I try to avoid a one-on-one platform fight because that doesn't really illustrate anything and the writing is wholly dependent on whatever assumptions one cares to make. I much prefer to illustrate a more general concept like ASW tactics or some overarching concept.

      I'm certainly open to ideas. For example, you've suggested a scenario. Now, what would be the overall concept, tactics, or whatever that the encounter could illustrate? Without an overarching concept it would just be an exchange of torpedoes with no idea of actual torpedo and sonar performance. If you have any ideas, let me know.

    2. You would have one Seawolf SSN on a Intel gathering mission around some Chinese artificial islands.
      However the SSN gets a little to close and is detected by a passive sonar array around one of the islands.
      They call some Chinese SSK on patrol to investigate, the Seawolf now is alerted on the closing SSK's from multiple directions,a game of nerves begin.
      What will he do if he tries to escape at full speed he could have a torpedo in the back, who will decide to engage first

  15. Just some thoughts:

    a) “The only problem I could foresee is that you'd like a ASW corvette to be acoustically isolated and that would an unlikely feature in a civilian ship.”

    I think that acoustically isolation is one of the most important features of an ASW ship. If an ASW ship can’t be heard by a submarine, than she has a real advantage and the odds are against the submarine.

    Regarding acoustically isolation in civilian ships: Norway’s Skipstenisk ship designer and shipyard has designed fishery and oceanographic research vessels, which have Underwater Radiated Noise reduction according to ICES 209.

    ICES 209 is explained here:

    My understanding is that cod, herring and similar species can’t hear such vessels at ranges in excess of 20 meters (see “7.4 Summary” at page 21).

    One such ship, an ST-369 design, 74,5 m. length OA, called “Cabo de Hornos” was build in Chile, for the Chilean Navy, for US$ 78.000.000.- She is a research vessel. Not being fast has good sea keeping and carries a lot of acoustic sensors.

    Maybe she could be re-outfitted for ASW during wartime.

    2) Regarding lightweight ASW torpedoes: when a submarine is there, you have to keep the submarine commander busy with an actual threat. All the time a torpedo must be in the water, i.e., you should launch one after another until the submarine is sunk or the contact is broken. ASW ships should carry lots of lightweight torpedoes.

    3) From the submarine point of view: There are some heavyweight torpedoes, like Blackshark, which swim out from the submarine. An explosion of compressed air does not launch them. It is much difficult to detect when a submarine launches such torpedoes.

    1. I took a quick glance at the links. Very interesting. However, I have no idea how relevant it is. For example, it would take very little "quieting" for something to become "silent" to a nearly deaf person but quite a bit more for a normal person. Similarly, how do fish compare to the electronic "ears" of a sonar receiver? Are fish acutely sensitive or nearly deaf by comparison? I suspect the latter. A sub can, under the right circumstances, hear faint ship noises many tens of miles away. Can a fish hear that? Again, I don't know but I suspect not. Thus, quieting for fish levels of "stealth" may be wholly inadequate for ASW work. Or, maybe it's plenty good enough?

      Also, the electronic "ears" of sonar are able to send and receive across a wide band of frequency whereas fish and fishing ship quieting seemed to be focused on a fairly narrow band.

      Do you have any feel for how fishery quieting compares to ASW quieting?

    2. "It is much difficult to detect when a submarine launches such torpedoes."

      Correct and that's just one of many aspects that makes ASW such a challenge. Conversely, it's very difficult for a sub to detect a purpose-built, acoustically quieted surface ship in the noisy environment of shallow waters even if the ship is occasionally using active sonar. A momentary, possibly distorted bearing, with no range, is not a firing solution. That's why shallow water sub-ship encounters are likely to occur at close range where the sub and ship almost literally stumble into each other! In such a case, there's not going to be time for a sub to slowly and carefully swim a torpedo out, send out along some offset path, then slowly and quietly guide it back towards the ship target. Instead, it's going to be a contest between the sub and ship to see who can launch the fastest and then evade the best. Subtlety will not be a feature of such an encounter!

  16. I'd love to read more of these scenarios, involving topics that have been discussed on this blog (various forms of ASW, amphibious landings, etc).

    Reading a discussion or list of facts can give you an idea for the concept but reading/watching a scenario like this or the linked video gives you a better feel for how things could play out.


    1. Thanks for the feedback. Most reactions have been positive to the story format so I'll make an effort to incorporate some more into the posts.

  17. I've often thought that a rocket-launched sonobuoy would be a useful addition to smaller ships. It could be fairly cheap if you used an unguided rocket to put a sonobuoy into the water about 5-10nm ahead of the ship and would allow triangulation with less ships and without the cost of drones/UUVs/helicopters.

    1. Now that's an interesting idea! Would you think you'd use a ship's gun to launch them (mini-Zumwalt AGS) or create some kind of trainable rocket launcher?

    2. Someone already tough of something similar

      A flight kit that can be retrofitted to existing navy sonobuoys. The preferred embodiment gives sonobuoys the capability of self-deployment, allowing them to be sent to a location remotely without the use of manned aircraft or recoverable unmanned air vehicles. This capability is advantageous in instances where it is desired to place a sonobuoy in an area hostile or hazardous to manned aircraft. The preferred embodiment is an attachment of a GPS navigation and control system, wings, control surfaces, and a propulsion system, onto a naval size-A sonobuoy

    3. I'd imagined something like the rockets the Royal Navy used in WW2 for illumination attached to the side of the forward gun. There's a tendency to over-engineer these things - it might be as simple as someone walking out onto a bridge wing with something like a bazooka because placement doesn't need to be that accurate.

    4. "There's a tendency to over-engineer these things"

      Quite true. However, buoy placement does require a certain degree of accuracy. They are generally laid in aligned strings according to precise patterns rather than just haphazardly. Thus, some type of basic fire/launch control is probably required - hence, the suggestion to use the ship's gun if the size is appropriate.

    5. A-sized sonobouys are only 124mm in diameter and could be deployed by something like the Israeli LAR-160 160mm artillery rocket system. That could be a nice multi-use system that would also help address the Navy's NGFS issues. Hell, you could just fit 9 or so in a single Mark 41 cell.

      There's also no need to reinvent the wheel. Even the old QH-50 DASH uav could drop up to 8 A-sized sonobuoys and stay on station to relay the data back to the ship. Using something like that to deploy a low frequency multistatic array in front of the convoy/task force could create a real headache for any sub commander.

      Also keep in mind that most new buoys, like the AN/SSG 565 and 573 multistatic buoys already have GPS receivers to improve the datum resolution. That receiver could be used to guide the buoy to the appropriate location.

    6. If you also used the rocket launcher to fire a hedgehog-like depth bomb you might be able to make the sub break cover. In the littoral, the ability to lob a sonobuoy over obstacles like islands or sandbanks could be very useful - helicopters could be very vulnerable to SAMs or even AA fire close-in.

  18. I too like the story format.

    But, in this scenario, the smart play for the submarine would have been to remain silent and not fire off a torpedo and let the ships pass. Or, avoid contact and maneuver to a safer firing position and fire off some antiship missiles, then skedaddle out of the area.

    1. "the smart play for the submarine would have been to remain silent and not fire off a torpedo and let the ships pass."

      Of course, the story would have been one sentence long: "Nothing happened as the ships cruised along their way." You probably wouldn't have liked the story as much!

      Seriously, though, you bring up one of the main benefits of the ASW corvette and that is presence. Consider your suggestion of the sub remaining quiet (and assuming that the searcher's active sonar didn't find it - could the sub take the chance that it wouldn't be detected or would it shoot first?). It would take hours for the ships to completely pass by. That's hours that the sub isn't conducting its mission - a mission kill of sorts. No sub is going to want to waste torpedoes and give away its position sinking a tiny, cheap corvette. However, the only alternative is, as you suggest, to lie quietly and wait for hours. Thus, the very presence of the corvettes can achieve positive results even without sinking a sub. That's what WWII corvettes so often did.

    2. First, I agree the Navy needs a fleet of smaller boats for ASW. Second, the Navy needs a replacement for the Cyclones for coastal patrolling.

      But, corvettes generally have limited endurance at sea, maybe 15 to 20 days, meaning 10 to 15 days on station. So, without continuous replacements, presence can be limited.

      It seems to me though that if the corvettes were using active sonar the submarine has a better chance to avoid detection. In this case, the submarine knows, or at least has a good idea, where the enemy ships are and providing it has room to maneuver, could avoid contact.

      I agree a squadron of small ships can tie up a sub from its mission. But, I'm sure there are plenty of examples where our subs successfully laid in wait avoiding detection from the surface during WWII. There's nothing wrong to live to fight another day.

    3. "corvettes generally have limited endurance at sea"

      Well, the Flower class corvettes of WWII were used extensively for cross-ocean convoy escort duty so that seems adequate and we should be able to at least match that in any new design corvette.

      "if the corvettes were using active sonar the submarine has a better chance to avoid detection"

      I urge you to read the reports, studies, and papers on the subject. The referenced Naval Postgraduate School paper that I cited in the post is a good starting point. The various reports all agree that active sonar, and continuous active sonar, in particular, is mandatory for successful shallow water prosecution. This is not my opinion, this is the consensus of scientific and professional studies. It may seem counterintuitive to you based on common knowledge of blue water ASW ops but the shallow water region is a completely different animal. Read the various papers and then see what you think.

    4. I read the Nelson paper and continuous active sonar is avoided in the submarine versus submarine simulation discussed in the paper. And, as the paper mentions, "Clutter such as sea mounts and biologics can distort, reduce, or confuse the signal such that detection is not certain even if the target is within the range required for detection." This was a blue water simulation and I would expect more diffraction of the sonar signal in shallower waters and I'm sure weather (e.g., rain, wind, etc.) is a factor too.

      But, a group is only as strong as its weakest link. So, a group of ships have to carefully coordinate their search pattern and use of active sonar. In the Nelson paper, it could take hundreds of hours for a single sub to detect another based on speed and sonar ping interval. But, a group of ships would have the advantage of having more ears in the water and detection time should decrease. Somebody must have done a simulation to this effect.

    5. "a group of ships have to carefully coordinate their search pattern and use of active sonar."

      You're exactly right and this is why I've harped on the need to be doing realistic training and tactics development instead of nearly worthless peacetime presence missions. In the middle of a shooting war is not the time to begin working on tactics.

      The tactics that I described in the post may or may not work but now is the time to try them and, hopefully, many other tactics out, see what works, refine them, and practice until we can do them flawlessly. This kind of experimentation and training will also reveal what ships and equipment we lack - such as an ASW corvette or RBU ASW mortar.

      Some people wanted to argue with the tactics I described but that wasn't really the point of the post, was it? The point was to suggest that a low end, non-helo, ASW asset could, with proper tactics, be effective. Whether the proper tactics were exactly what I described was not the point.

      You've hit on a key aspect - the need to train to perfection and continuously work to develop new and better tactics. This is why the Navy's refusal to buy a few SSKs for training purposes is so baffling. For most ships, their first ASW encounter with a SSK will be in a real war. We don't have any systematic ASW training against SSKs and only occasionally and sporadically run a simplistic set-piece exercise against a foreign SSK if one happens to be available.

    6. I'd go a step further and suggest the Navy buy 10-12 conventional subs at the expense of 3-4 SSNs. Aside from being useful for ASW training, they could be used for regular coastal patrols and maybe special operations.

      I'd also be careful about how low-end you want to get with an ASW corvette. I think any proper ASW corvette needs to be able to support a single Seahawk. A squadron of 3-4 ships with 3-4 helicopters provides more flexibility in your tactics and can expand the search area.

    7. "I think any proper ASW corvette needs to be able to support a single Seahawk."

      You can think that but you can't afford it. The main characteristic of a corvette is numbers which means it has to be cheap. By the time you add a flight deck, hangar, additional crew quarters, more food storage, additional fuel storage, additional magazines, helo maintenance shops, additional parts storage, etc. you've moved from a cheap corvette to at least the LCS. Recall that the LCS was the Navy's attempt to build a $200M affordable ship and it's now $500M-$600M WITHOUT a module.

      Wishful thinking is nice but it's not realistic. No one, least of all me, is suggesting that helos aren't useful for ASW. The reality is that we can't afford a navy where every platform is a super capable, super expensive one. The ASW corvette won't be the primary ASW asset so why gold-plate it like one? We found out that we couldn't afford the 55 LCS we wanted (and, of course, they had other problems) so what makes you think we can afford 100 or more helo-carrying ASW corvettes which is, essentially, what the LCS is?

      Again, wish all you want but the reality is your wish isn't feasible.

      "A squadron of 3-4 ships with 3-4 helicopters provides more flexibility in your tactics and can expand the search area."

      This is not the job of the ASW corvette. You seem to think that the ASW corvette is the only ASW asset I think is needed and that it will do all the ASW work. That's not even remotely true. Very few ASW corvettes will ever actually find and attack a sub.

      I've also described true ASW destroyer escorts WITH helos and true destroyers with ASW capability. I've also described a need for ASW hunter-killer groups centered on small ASW carriers.

  19. How much time does it take for any modern submarine to develop a fire solution, id imagine with advanced computers and special algorithms it would be seconds?

    1. The firing solution is continuously calculated so it's always ready. However, you're undoubtedly familiar with the computer saying, "Garbage In, Garbage Out"? The firing solution is only as good as the data being fed into it. This is where a few commenters are failing to understand the shallow water environment.

      The shallow water environment, unlike the relatively clean open ocean environment, has overwhelming biologics noise, tidal ebb/flow noise over the bottom, river feed noise, immense flow noise from wrecks, garbage on the bottom, rocks, etc. as well as, generally, lots of civilian fishing vessels. Even an active sonar from a searching ship is not an instantaneous firing solution for the sub. The analogy would be trying to spot one particular individual shouting in an arena full of noisy people. The active ping is distorted as the return bounces off the bottom, is reflected off wrecks, rocks, and bottom debris, is swamped by flow noise, etc. and, of course, provides no range figure. The sub may get an indication of an active sonar signal somewhere across a wide bearing range but that's far from a firing solution. Over time, with many more signal data points, the bearing can be refined, the range can be estimated, and the course and speed of the target can be established. So, yes, the firing solution is continuously updated but it is initially garbage and is slowly refined.

      There are a few commenters who seem to believe that with a single ping by a searching ship, the sub will instantaneously launch a torpedo with a 100% target certainty. This is ludicrous. If one takes the time to understand the physics of the acoustics of shallow water one quickly realizes that detections are very difficult for both the surface ship and the sub. Detections are likely to be very close range.

      Does this make sense to you? If not, you have two choices: take my word for it because I've done the research and established a pattern of reliability in my posts or, if you don't believe me, go do the research yourself and come to your own conclusion - which, if you do the homework, will be the same as mine in the end.

      I've spent about as much time as I care to correcting misconceptions by uninformed readers.

    2. Thanks, i was not doubting just was curious how long it would take.

    3. Even under perfect conditions, a single active ping only provides the sub with a bearing. No range, course, or speed. Where does the sub "aim" the torpedo? At the target, to the right, or to the left? The sub has no idea because it has no course, speed, or range for the target. Guess wrong and you not only miss but you likely give away your own position. So, the sub waits, collects more data and slowly refines the firing solution. Submarine warfare is a slow, patient game. A few readers do not understand this and have no interest in learning.

      I offer the knowledge from my research but I can't make someone accept it. For those who won't, I'm not going to waste my time debating simple reality.

    4. "So, the sub waits, collects more data and slowly refines the firing solution."

      Now im starting to image a SSN duel in the deep blue sea, that would literally be a cat and mouse game, whoever gives up his position first is dead for sure.

    5. And this,

      Russia’s Deadliest Subs to Receive New Heat-Seeking Torpedos

      has the US experimented with heat seeking torpedoes ?

    6. I'm unable to verify that article. I can find lots of repeats of the article, all quoting the same source. I suspect it's a misprint (whether intentional or not). I can find no ohter source that talks about a heat seeking torpedo.

      I find it difficult to believe that IR wavelengths could be detected underwater at tactically useful distances.

    7. Thats they're newest torpedo they acknowledged it last year, thats the nose section ( i would speculate that the heat seeker is for terminal attack)

      here are two other articles that mention heat seeking

      Another system that they claim uses heat seeking

    8. "There are a few commenters who seem to believe that with a single ping by a searching ship, the sub will instantaneously launch a torpedo with a 100% target certainty. This is ludicrous. If one takes the time to understand the physics of the acoustics of shallow water one quickly realizes that detections are very difficult for both the surface ship and the sub. Detections are likely to be very close range."

      You bring up a good point. Back in 2009 the Netherlands did a continuous active sonar test with three different pings that comprised 90 time of one standard ping duration. The idea being cutting the time needed for a solution by three. They claim to have got the same range using 11db less power. I have no idea how they did that but the physics would be interesting. Reducing that much power would go a long way with reducing side lobe instead of dealing with it on the receive side.

      The navy took that up and this year asked for bids on a non-cots signal processor for CAS.

      I think the CAS is an exciting development because of how the Navy has historically conducted ship vs. sub warfare during the cold war, which was/is drive the sub away using active sonar. Short answer, make the frigate a target and geographically space the ships out to make an attack on the carrier a suicide mission(in theory if not always in practice...LOL).

      Obviously, sound being slower than electricity the speed to detect/range will never be like radar. But with continuous improvement western navies are not just shortening the time it takes to get a range and bearing but doing so at a longer distance. At the same time they are changing the way asw is conducted.

      While some of what you've talked about is valid for stalking subs, during the late cold war subs stalked subs and ships influenced how/where they drove(various forms of picket duty).

  20. A scenario I'd like to mention is one where enemy subs are off our coasts and ports. These ASW corvettes would be needed here. We would also need MCM capability.

    1. For this, USCG cutters and aircraft should be augmented to perform coastal ASW and limited MCM.

    2. It's not a bad idea but using CG vessels for ASW would require new construction vessels as current ones have no acoustic quieting, sonar, or ASW capability that I'm aware of.

      The same is true for MCM work.

    3. ASW systems could be added via modular components. There are a number of small LFATS VDS systems out there now that fit in a 20' TEU container. There are removable dipping sonars and sonobuoy dispensers for helicopters.

      Same goes for MCM. There are lots of small MCM components and USVs out there. These could be shore-based for port security.

      Not ideal, but better than nothing. And better than solely relying on the Navy.

  21. I'm sold on the need for 20-40 cheap ASW corvettes, but that still leaves a lot of questions about the details:

    - How fast does it need to be? Slower is cheaper, and while nobody expects it to be able to keep up with a CVN, it would be nice to be able to keep up with a CVN battlegroup (at least as well as the Perry's could). I guess that means sprints of ~28 knots need to be possible?

    - I get the 'we can't afford a helicopter' but could we afford a UAV like a Fire Scout modified to drop sonobuoys (or maybe even a single Mk-54 torpedo)?

    - To both maximize the ASW capability and reduce the chance of a rock-paper-scissors loss to a random enemy surface combatant, a heavyweight (Mk-48) torpedo launcher could be included. They couldn't be used against subs near high-value friendlies. But I have a lot more faith in the Mk 48 than Mk 54 (ASROC or otherwise). And assuming the corvette survives the AShM's from some random marauding surface combatants, the Mk 48's would devastate anything trying to close within ~20 miles.

    The beauty of this option is one system makes the corvette much better against both subs and surface ships. No need to add an NSM or Harpoon!

    - It probably still needs a lightweight Mk 54 launcher for when you don't want to risk a big Mk 48 reaquiring a friendly ship (full of Marines) by mistake... But does it need an ASROC launcher? If so, how to minimize the cost? No VLS, right? So an old 8-cell box launcher?

    - The RBU makes a lot of sense, but it is probably the most controversial element in the whole design. It might be old for the Russians, but it's new tech for us. That means we should probably figure it out before mass producing... The ASW corvette is still viable without it.

    - I assume it needs some minimal AA self-defense equipment including 3D radar, Nulka decoys, ECM system, Phalanx, and RAM launcher (no VLS to keep it cheap) to survive missile attacks.

    - And I assume it needs a Mk110 57mm for the random Chinese Coastguard flotilla or whatever.

    And perhaps most importantly, with (most) of the above, plus sound isolation, a variety of sonars, and possibly even hardening, could it be built for less than $500M??? I mean, could the US build it for less than $500M?

    1. "it would be nice to be able to keep up with a CVN battlegroup"

      NO! The ASW corvette that I've described is NOT a battlegroup escort. It is a peripheral patrol vessel, convoy escort, chokepoint monitor, littoral hunter/killer, etc.

      This ties into my overall vision of fleet composition. In addition to ASW corvettes, we need a pure, larger, non-Aegis ASW destroyer to provide exactly the battlegroup escort that you mention.

      The problem I have with posts is length. I have only a few paragraphs to work with. So, if I describe an ASW corvette, everyone assumes that I mean that to be the only ASW asset in the entire military and they immediately proceed to tell me why that can't work. I've described the other units that are needed in other posts and comments but I simply don't have enough room in any given post to reiterate my complete naval force composition each time. I'm working on an added, permanent force composition page that will lay out the numbers and composition of the fleet, as I see it, and provide the context for readers to evaluate individual units in.

    2. "I assume it needs"

      No, no, no. The key attribute of an ASW corvette is numbers which implies both the requisite expendability and affordability. We can't add anything that isn't directly ASW related. Now that you know, from my previous reply, that the ASW corvette is a peripheral vessel, you can see that gearing up is not required and will only increase cost which will decrease expendability and numbers.


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