Friday, April 19, 2013

I Feel The Need, The Need For Speed !

ComNavOps continually analyzes naval performance and the features and characteristics of the Navy’s ships and planes.  One of the characteristics I’ve long wondered about is the requirement for high speed in our surface combatants.  As best I can tell, our requirement for 30+ kts came from the operating doctrine developed for fleet carriers during WWII.  Carriers would make a night run-in towards a target (a Japanese island), launch a dawn strike, recover, and vanish before an effective counter-strike could launch.  This was an effective tactic because long range radar (both land and airborne) and satellite surveillance did not exist.

Later, high speed was found to be necessary to assist in the launching of planes.

All other ships had to be capable of 30+ kts in order to keep up with the carriers.

Now, however, we can launch planes from a motionless ship even with today's steam catapults.  Also, the existence of AEW, SOSUS-like arrays, satellites, etc. all provide long range detection and would generally negate the run-in tactic.  So, what is the tactical usefulness of 30+ kts of speed?  It won't let you outrun or outmaneuver a missile.  It won't even let you outrun an Iranian speedboat.  Now don't get me wrong.  I think speed is one of those things that's always nice to have.  It's just that I'm not able to come up with many tactical scenarios where 30+ kts provides a significant advantage over, say, 25 kts.  I assume most of you know what the power curve is like.  Once you get past 20 kts, each additional knot comes with a hefty power/weight/equipment cost.  I just wonder if 30+ kts is still worth the cost in weight/internal machinery volume/dollars/maintenance/fuel capacity?

The extreme example of this is the LCS which has a ton of speed but had to sacrifice enormous weight and volume margins to achieve it and it apparently has no tactical relevance that anyone has been able to elucidate.

The only scenario that seems even moderately plausible is attempting to outrun a torpedo.  Now, modern torpedoes are capable of well over 30+ kts (40-60 kts) so actually outrunning one isn’t an option, however, the ability to maintain a dwindling lead over a torpedo long enough for countermeasures to work or for the torpedo to run out of fuel is valid, if unlikely.  And, to be fair, maybe this scenario alone justifies the speed built into all surface combatants.  I just wonder, though, if we aren’t holding on to a requirement from the past that has only marginal usefulness today.  Could some of that weight and volume that's dedicated to generating the last few knots be put to better use, like armor, weapons, or electronics?

In short, I have mixed feelings about this.  Anyone want to make a strong argument for or against speed?

29 comments:

  1. I believe that the 30kt. requirement is still about keeping up with the carriers, but now it's less about tactical utility and more about strategic mobility. Nuclear powered aircraft carriers can steam at full speed anywhere in the world. Their escorts need at least some capability to keep up with them, even if it requires a lot of replenishment to keep them fueled.

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    1. I certainly get the strategic mobility idea, however, even that is somewhat questionable. Consider a 1000 nm transit at 30 kts (33 hrs) vs 25 kts (40 hrs). Will the 7 hour difference make a critical difference? It could but that seems unlikely especially in today's world where events of that critical importance don't just happen overnight. If N. Korea or Iran wanted to start a war, there would be build up period of forces being readied and repositioned and we would have plenty of notice and transit time.

      As I said in the post, I'm not at all against speed - it's great to have - but I wonder if the weight/volume penalties couldn't be better spent on other capabilities.

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    2. I agree with you, that seven hours probably won't make much of a difference. You still have to keep up with the carriers, though. Since a CVN has the power do 30kts into hostile waters, the escorts have to at least theoretically be able to arrive at the same time to protect it when it gets there.

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    3. Anon: "You still have to keep up with the carriers, though."

      Or... The carriers could slow down by 5kts.

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    4. I seem to recall reading that during WW2, few (zero?) ships travelling over 25 kts were successfully attacked by enemy submarines.

      High speed is just about the only advantage an aircraft carrier has over an enemy submarine. Particularly now that the carrier air wing is bereft of long-range ASW capability.

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    5. Anon, yes, ships travelling at high speed posed a problem for WWII era subs. Those subs were limited to an underwater speed far less than the surface ships which made intercept geometry very difficult. Also, the torpedos of the day were about the same speed as the surface ships and relatively short ranged. Today, however, subs are faster underwater than surface ships by a good margin. Also, today's torpedos are much faster and longer ranged. For example, the Soviet 650 mm torps are credited with 50 kts for 30 nm or 30 kts for 60 nm. The carrier's speed "advantage" is non-existent. This isn't to say that speed isn't good. It is! My point is that 30 kts versus 25 kts won't make any difference tactically and imposes a major weight/volume penalty.

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    6. The majority of threat countries (i.e. non-US, non-allied) field diesel-electric submarines. Most of our potential enemies field relatively few if any SSNs, with the obvious exception being Russia.

      If you examine the PLA Navy, they've only got about 7 SSNs but close to 50 diesel-electric boats. And they are cranking out modern diesel-electric boats (KILO, YUAN, etc.) at a much faster rate than nuke boats.

      Diesels are significantly slower than surface ships. Top speed is usually about 15-20 knots, and then for only short periods of time. High speed for a surface ship is a definite advantage.

      I'm not sure how you can generate a reliable targeting and identfication solution at 60 nm. It's analgous to the problem we had with radar-guided missiles in the '60s - the weapons tend to outrange the sensors.

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    7. Anon, you are correct about the composition of most potential enemy submarine fleets. I don't consider Iran, N. Korea, or the odd third world trouble spot to be much of an issue, from a combat perspective. I don't see Russia as a potential enemy. Regardless, the point of the post was that we gain little or nothing from the quest for the last few knots of speed. As you indicate, a diesel sub speed of 15-20 kts for a brief period is already well below that of surface ships. That last squeeze to get from 25 kts to 30 kts is what I'm talking about. It serves little tactical purpose.

      If you've been following this blog, you'll no doubt be aware that the thrust of my commentary is largely geared at the future. So, too, with this post. In 10-20 years China will, undoubtedly, have many more nucs with inherently superior speed compared to surface vessels and fast, long ranged torps. Continuing to build surface ships to an arbitrary 30 kt standard is simply wasting weight/volume margins to no good purpose. The discrepancy between submarine/torpedo performance and surface ship speed is too great for a few more knots to matter. That's my point. The weight/volume penalty would be better spent on other equipment.

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    8. I appreciate the spirited debate!!!

      Nothing I've read open source indicates that PLA Navy will be producing SSNs in quantity within the next 20 years. They appear to be mass-producing lots of cheap, relatively effective diesel-submarines. Perfect for coastal defense and patrol.

      High-speed limits your overall exposure in a submarine threat area. Assume you're trying to get from A to B, and an enemy puts a barrier of diesel subs in front of you. The faster you can transit through the area, the less likely you are to encounter an enemy sub.

      I do agree that there is probably a logical limit to how much speed you want. But it also depends on what you type of ship, and what you get in the tradeoff.

      I think we'd agree that the 40+ knots for LCS is excessive. I see value in an LCS Mark 2 that does about 30 kts, and "trades off" 10 knots of speed for endurance. Endurance is critical to an ASW combatant.

      However if we are talking about an aircraft carrier (which cannot detect or fight enemy submarines) I would be very hesitant to sacrifice any speed.

      The advent of Air Independent Propulsion (AIP)and similar technolgies will significantly increase the effective submerged speed of diesel submarines. If we're designing carriers to last 50+ years, I'd want to keep a healthy speed margin.

      http://en.wikipedia.org/wiki/Type_214_submarine

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  2. I agree with anon we need speed for strategic mobility. Com, you should look up "A New Energy Age for DoD" by the Throium Energy Alliance. Alot of the stuff they talk about, like railguns with a 6,000 kilometer range, are far out but slide number 29 is not.

    Getting a battle group or task force to a crisis point rapidly is vital to the Navy and the executive branch.

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  3. Ships get lighter, I mean less armoured, but also slower than their WWII counterparts. An extra 5 knots puts you an extra 5+ miles away from the threat - in any direction: that's a lot of sea.

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  4. Carriers still turn into the wind and move to flank speed when launching aircraft. Yes, you could launch most planes using just the catapults, but only with reduced fuel or payload.

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    1. They do but it's mostly for an added margin of safety in the event of a poor cat shot. Fully loaded planes can be launched just fine with 25 kts as opposed to 30 kts. My question is not whether a ship needs any speed, just whether the additional five knots is worth the weight/volume penalty.

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  5. Outrunning a torpedo is foolish, but there is an ASW benefit to speed. A ship that can go 30+ knots presents a very difficult targeting problem for a submarine.

    Most diesel subs can't go more than about 20 knots, and doing so for anything over about an hour exhausts their battery. In contrast, a nuclear submarine that goes 30+ knots in an attempt to catch a ship would be extremely loud, and thus easier for ASW forces to detect.

    I've argued before that as an ASW platform, about the ONLY thing the LCS has going for it is a) speed and b) a larger helo deck/hangar. If it can keep sprinting around and stopping only long enough to launch/recover an MH-60R or VTUAV, LCS might actually provide some value to the ASW fight.

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    1. You point out that 30+ kts makes a difficult target for a sub. My question is whether 30 kts offers a significant advantage over 25 kts. If so, how?

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    2. It's really all "limiting lines of approach" -- where the submarine must be in order to launch a torpedo, given its own speed and the speed of its target. It's all vectors and geometry but essentially:

      - If the sub and the ship are the same speed, then the ship essentially has to worry about an attack from nearly any direction (execpt directly behind).

      - If the ship is faster, it doesn't need to worry about attacks from its rear quarter, only threats from the flanks and dead ahead.

      - If the ship is a lot faster (say 10 kts), it really only needs to worry about threats directly ahead and on the 'close-in' flanks. It can outrun anything behind it or at significant distance on the flanks.

      According to Jane's the max 'silent' speed of an Akula SSN is 28 knots. So an LCS which can sprint at 35-40 knots presents a very narrow window through which the sub has to proceed in order to get within firing range.

      I could see some interesting tactics being built around the high speed of LCS. The ship could sprint ahead at 40 kts, slow down and deploy its sonar, and then use its helos to localize and engage any contacts. It could then sprint ahead to a new position to recover the helos.

      It's far from what we're used to doing with a conventional ASW frigate, but as long as the ship keeps moving (and doesn't run out of gas!) it'd be very hard for an enemy submarine commander to target.

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    3. I should've added that I don't believe the 'trades' made in the LCS design to gain high speed are generally worth it. It's really a niche capability.

      Using my limiting lines of approach example above, but against a slower diesel submarine (max of 17-20 kts), a top speed of 30-35 knots is more than ample to keep an ASW ship mobile and out of harm's way.

      If I was given the proverbial 'blank sheet of paper' to design an ASW frigate, I'd take increased endurance and sea-keeping over (very) high speed. But if we are stuck with high speed as a key performance characteristic on the LCS, we'd best well figure out how to use it.

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    4. Anon, while I think I understand your lines of approach concept, are you fully taking into account the fact that modern torpedos are capable of 60 kts? The need for the submarine to closely approach the target is greatly reduced with that kind of weapon. On the target side of things, 5 more knots against that kind of weapon seems unlikely to change the outcome. Further thoughts?

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    5. The point's really not to avoid the weapon; it's to stay out of visual range of the submarine so he can't get a good shot.

      While a heavyweight torpedo can theoretically reach quite far (Wikipedia lists the max range of the MK-48 as around 20 nm) that's not what's driving the tactical engagement.

      I'd postulate that just as in air-to-air engagements, an enemy submarine will have to get within visual range to positively identify the target before launching his torpedo.

      Assuming a 6 ft periscope height and 45 ft ship mast height, the maximum visual horizon for a submarine is about 10 nm. And that's assuming perfect weather, no visual deception, etc.

      The more I think about -- something like the LCS (fast, low to the water, and with LCS-1 style camo scheme) might actually present a fairly difficult targeting problem for an enemy submarine.

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    6. Ummm... That's not really how submarine attacks work. Target ID is not visual, it's acoustic. The target's sound signature is all that's needed. It would be a relatively rare attack that used visual methods. The act of raising a periscope exposes the sub to radar and visual detection.

      With that in mind, the LCS and its incredibly noisy water jets will be the most obvious target for many miles around.

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    7. With respect... what are you basing that on?

      I think what you are laying out is how a submarine attack could works in a perfect acoustic environment (deep water, open ocean) with a US submarine and its crew.

      Acoustic identification requires sophisticated passive sonars, enormous processing capability (power and cooling) and significant manpower and expertise. All of which are in very short supply among most threat submarine fleets -- which tend to operate small diesel submarines.

      Even with sophisticated acoustic equipment, it is still incredibly difficult to conduct acoustic target motion analysis (TMA) in the noisy and crowded littorals. See the USS Greenville collision in February 2001... or or any number of US submarine collisions in the last decade.

      There are also ROE concerns. Submariners generally like to know exactly what they are shooting at. Acoustics won't do that to 100% certainty -- unless you are very, very good at it. If you want a historical datapoint, HMS Conqueror attack against ARA Belgrano was conducted following periscope observation.

      Lastly... if periscope observations are so rare: why is the US Navy investing so much money for sophisticated periscope detection radars on its maritime patrol aircraft, ASW helicopters, and now on its aircraft carriers?

      http://www.navy.mil/navydata/fact_display.asp?cid=2100&tid=1300&ct=2

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    8. PS. I forgot to add that it's a bit more complicated than simply saying that LCS water-jets are incredibly noisy.

      From what have read, a water-jet may actually help with the ship's overall acoustic signature in that they remove propeller vibration and cavitation. These tend to be big noise producers at high speeds.

      And even something that is noisy isn't necessarily easy to target. I'd imagine that the sound energy put out by a water-jet would more like broadband noise vice a discrete frequency. It might be easy to detect, but hard to pinpoint.

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    9. Anon, you have some unusual beliefs about submarine operations. I'll leave it at that other than to suggest you check out the fairly large selection of books in the public domain that describe submarine operations. Some of the Cold War books are quite good.

      The Navy is investing in radar detection of snorkling subs.

      The Navy's sub collisions are the result of negligent watchstanding procedures not any difficulty in acoustic targeting and identification.

      Iran, N. Korea, and China are not going to be very discriminating about letting loose with torpedos. Iran proved that target identification was not a concern during the Iran-Iraq Tanker War. Visual ID definitely won't be a requirement for them!

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    10. I don't think my ideas are that unusual, but I can see how you would think so if your only sources of info on ASW is something like "Blind Man's Bluff". It's a great book, but not sure it is relevant to future ASW fight:

      (1) These books mainly depict the interactions between first-peer powers (NATO vs. Soviet Bloc) fielding very large fleets of nuclear powered submarines.

      The threat today comes mainly from fleets of small, cheap diesel submarines, with fairly limited performance and acoustic capabilties. These boats share more in common with a WW2 Type XXI than a 688 class.

      (2) Cold War books generally focus on 'sexy' submarine-vs-submarine interactions, in which passive acoustic sensors were quite logically the ONLY available means of identification.

      (3) The primary environment in which the Cold War was waged (N. Atlantic) was a broad open ocean expanse with very good acoustics. The next war will likely be waged in one of three extremely poor acoustic environments: the South China Sea, the Yellow Sea or the Arabian Gulf.

      I'd recommend reading up on US ASW operations versus Soviet diesel subs in the Med - which was/is a relatively noisy and poor acoustic environment. Periscope exposure by Soviet Bloc subs, and detection by US ASW force was actually quite common. That's the kind of fight we'll have.

      As for whether the enemy will need to identify in wartime, that's completely debatable. My thought is more that the acoustic environment and limitations of their doctrine, equipment, and training will probably force them to do so.

      I do however think it's oversimplification to the extreme to lump China (rational actor) into the same category as Iran (unstable theocracy) and North Korea (corrupt despot). They don't think the same, and might not act the same.

      Snorkeling is a total different beast, and actually might become less of a vulnerability with widespread proliferation of Air Independent Propulsion (AIP) and related technologies. If you do think periscope exposure is not an area of interest for the Navy, can you please explain why:

      - the APS-153 radar on MH-60R is designated by the Navy as the Advanced Radar for PERISCOPE DETECTION and Discrimination (ARPDD).

      - the APY-10 radar mounted on the P-8A is described by the Navy as being optimized for PERISOPE DETECTION.

      - the SPS-47 radar mounted on the CVN is described by the Navy as a PERISCOPE Detection Radar (PDR).

      - the Sea Giraffe 3D radar (supposedly?) being installed on the Littoral Combat Ship has a PERISCOPE detection capability.

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    11. PS - in reviewing my response, I see that it comes across a bit on the snarky side.

      My apologies for that. ASW is a topic which I'm very passionate about -- even if most of the Navy is not!

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  6. Ships travel in fleets. The Fleet goes as fast as the slowest ship so thats the fleet replinishment ships...so around 20kts.

    So why do they really need to go much faster?

    There are now torpedo's with 120+ mi ranges there have been missiles with far more than this anyways. And 55kts is nothing for a antiship missile or a round from cannon or even a rifle.

    So should a DDG or Carrier need 30+kts? Sure All of the ships like the LCS need to go 55+ kts? Hell no.

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    1. James, you lost me on your last sentence. Are you saying that DDGs and carriers need 30+ kts? Or, are you saying we don't need 30+ kts. Clarify that last sentence for me, if you would. Thanks!

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    2. I'm saying that the idea of the LCS needing to go 50+ kts is false. The Absolons could do the same jobs as the LCS fine. And be better at it.

      I think the question is this. Our ships can go 30+ kts ok but what then? They run out of fuel and supplies because the ships carrying them are still chugging along at 20 kts.
      The Carriers have 30+ kts just because of those nuclear reactors. The others use gas hogging turbines which means they need a lot of resupply. At 20kts a DDG-51 has 4,500 nmi. At 35 which i figure is approching its top speed its a lot less. So...

      Honestly I'm just not sure. Me I'd say no not really. Ships like DDG's are going to operate in a fleet with a lot slower ships so...whats the point. You have to stay and guard the rest of the fleet. If we have a specific sub hunter sure otherwise.

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  7. James: Your last sentence. Yes, unless they are in hunter/killer groups (eh - perhaps not that likely) or detached from the fleet/task force/gaggle of geese (hey, who says we can't chuckle once in a while) to hunt down a retreating attack sub- which a helo would just as well or perhaps better. So it seems that if a carrier strike group IS always tied to it's supply ships than "carrier" speed isn't required for escorts. Nice, but more historical than tactically necessary. Then, what do I know, I was an 11-B and then infantry branch so all I know is scouts out - engineers up - follow me.

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