Escorts

The key to understanding this post is grasping and accepting that the engagement window for a ship to defend against attacking missiles will allow just 4 shots per target (see, “Engagement Range”).  Most of us have grown up seeing WWII videos of ship anti-aircraft gunners pouring thousands of rounds into the air as the enemy planes slowly approach and then enter their terminal dives and weapon releases.  Each target engagement can last for several minutes.  This is no longer the case.

While I view history as timeless in its lessons, irrespective of technological advances, this is an example where technology has altered the details, if not the fundamental concept.

Each target engagement will last 4 shots.  It doesn’t matter how many missiles you have in your magazine, you’ll only get 4 shots per target.  If you don’t understand this, there’s no point reading the rest of the post.  This is not an opinion on my part, this is simple and pure physics.

With that out of the way …

One of the problems that has become obvious over the course of many posts and comments is that most people do not understand the concept of escort vessels.  Really?  What could be more simple, you say?  You assign a couple of Burkes to provide anti-air (AAW) protection and, of course, being multi-function, they have the added benefit of being able to provide anti-submarine (ASW) protection, as well !  Well, there’s a little more to it than that.  In fact, there’s a lot more to it than that!

Unfortunately, far too many observers/commenters believe that around 2-4 escorts is sufficient for a high value target (HVU) like a carrier, convoy, or amphibious group because that’s all they’ve ever seen the Navy operate.  The more extreme observers might call for 6-8 escorts.  However, even this is woefully insufficient and now we’re going to see why and we’re going to correct this misconception.

As always, let’s begin with a review of history.

Historical Escorts

We forget just how many escorts a WWII carrier task force required.  Admiral Marc Mitscher described the escort requirements of a carrier task force in the following statement from Wikipedia.

Said Mitscher: “The ideal composition of a fast-carrier task force is four carriers, six to eight support vessels and not less than 18 destroyers, preferably 24. More than four carriers in a task group cannot be advantageously used due to the amount of air room required. Less than four carriers requires an uneconomical use of support ships and screening vessels.” (1)

The support vessels were cruisers and battleships.  Combined with 18-24 destroyers, the total escort requirement was 24-32 ships – a quantity that seems shocking to us, today, because we’ve forgotten the requirements of combat.

Having reminded ourselves of the historical precedents, let’s conduct an analytical examination of today’s requirements.  Escorts are needed to perform two basic functions:  anti-air protection and anti-submarine protection.  Additional functions such as electronic warfare and anti-surface protection are also required but can generally be performed by the AAW or ASW vessels.

Anti-Air (AAW) Escorts

There are several aspects to consider when discussing AAW escorts.

Threat Axis.  Unless you have absolute knowledge about the enemy’s attack plans – and you never do – the threat axis is unknown.  Yes, you may well have a general idea of what direction an attack will come from but a ‘general idea’ is far from certain. 

In WWII, the identification of the threat axis was a bit more obvious.  While aircraft could, and did, attempt to circle around and try to approach from alternate or several angles, their ability to do so was limited by their range.  Attacking aircraft were generally near their maximum range by the time they reached the target and began their terminal attack runs so they rarely had the fuel required to perform wide swings around their targets to approach from unexpected directions.  Additionally, wide swings provided more time for the defensive aircraft and AAA to attrite the strike so the strikes generally made fairly straight approaches with just some terminal maneuvering, especially for torpedo attacks.

Today, cruise missiles with thousand mile ranges can use waypoints to approach from any angle.  Therefore, every axis is a potential threat axis although more direct axes still have a somewhat higher likelihood of attack.

So, to cover ever axis requires that the escorts be arranged evenly in a circle around the high value unit they’re escorting.  This, alone, would suggest the need for at least a dozen or more escorts.

Effective Engagement Range.  We’ve previously discussed that the most likely AAW engagement scenario involves sea skimming aircraft or missiles that are detected at the radar horizon (call it 20 miles, optimistically) (again, see, “Engagement Range”) and that engagements will involve short/medium range ESSM missiles with very brief engagement windows.  Two salvos of two missiles each would be a fortunate engagement.  That being the case, those marvelous ships with a thousand VLS cells are pointless, as we’ve pointed out in the past.  Each ship, regardless of how many VLS cells it has, is likely to only get off four defensive missile shots per engagement.  That being the case, it is obvious that the only way to get more missiles into the engagement is to have more ships since more VLS cells per ship doesn’t help.  This, again, suggests the need for as many AAW escort ships as possible.  Thus, one would like to have 2-4 ships along every threat axis.  The arithmetic on this quickly leads to very large escort numbers.

Probability of Kill (pK).  It’s necessary to consider the defensive pK against attacking missiles when trying to determine the required number of escorts.  For example, if the pK is very high, you only need a few escorts because you only need a few defensive missiles but if the pK is very low then you need lots of escorts to make up for the individually low pK (recalling that each ship will only get a very few shots per engagement). 

So, what is the pK?  Well, that depends in great measure on the geometry of the intercept.  If the attacking missile is coming straight at you, then the geometry is simple, your defensive missile is not required to maneuver, and the pK is high.  At the opposite extreme, if the missile is going past you (nominally, a 90 degree off-axis defensive shot), aimed at some other ship/target then the pK is going to be very low because off-axis shots require a great deal of maneuvering by the defensive missile.

The reality is that modern attacking missiles, even one coming straight at you, enter into wild, violent, evasive maneuvers in the terminal attack phase precisely to make the defensive shot a somewhat off-axis shot and, thus, a lower pK.

There is very little data available on actual naval defensive missile engagements and what there is, is not encouraging.  Historically, the pK of defensive missiles, even against direct attacks, is 5%-25% (see, “AAW”). 

It’s readily apparent, then, that if the escort is not the main target, which it usually isn’t, the defensive pK will be very low which requires that multiple escorts be placed as nearly on the direct threat axis as possible.  The only way to ensure direct threat axis placement is with large numbers of escorts distributed evenly around the escorted target so as to ensure that there are at least some escorts in the direct path of the attacking aircraft/missiles.

Layered Defense.  The best defense is one that begins as far out from the HVU as possible.  Recognizing that the most likely engagement will occur at radar horizon distances (15-20 miles), the only way to push the initial engagement out from the HVU is to create multiple defensive layers of escorts spaced at 15-20 mile intervals out from the escorted high value unit so that the attacking aircraft/missiles have to pass through multiple layers and multiple engagement opportunities in order to get to the HVU. 

We did this in WWII with distant rings of destroyers backed by closer rings of cruisers and, finally, a very close ring of battleships (the WWII equivalent of Aegis).  To get, say, three rings requires a radius of 45-60 miles which means a 90-120 mile diameter defensive sphere around the HVU!  When one contemplates the number of ships required to attain effective engagement density across a 90 mile diameter defensive circle and still cover every threat axis, it becomes instantly apparent that many, many escorts are needed.

Positioning.  Modern aircraft and missiles are far too fast to allow for escort repositioning once an engagement has begun.  Whatever position the escorts are in when an attack begins is the position they’ll have to fight from.  Thus, we must have enough escorts to provide adequate protection from any axis.  Repositioning during an attack is not an option.

Anti-Submarine (ASW) Escorts

If the ASW function resides on ships separate from the AAW function then the escort requirement further increases.

Engagement Range.  Modern subs have torpedoes with ranges of up to 60 miles.  It is vital to detect and engage subs beyond their torpedo range to the HVU.  That means engaging at ranges of 60+ miles.  Given the slow pace of ASW engagements, great standoff distance is also necessary to allow the HVU to continuing advancing while the ASW engagement is being conducted.  If ASW engagement begins at, say, 20 miles, the HVU would have to immediately turn away and begin a high speed run in the opposite direction.  This is counterproductive in getting the HVU to its destination.

Subs also have guided missiles with ranges of a hundred miles or more although this becomes an AAW problem at some point.

Numbers.  WWII demonstrated that the most important factor in successful ASW was numbers of ASW assets.  The Cold War simply reinforced this lesson.  Thus, having a single ASW escort in any engagement is unlikely to produce a positive result.  Successful engagements will require multiple ASW assets.  Now, not all of the numbers need to be ships.  Some/all of the assets can be aircraft but, ultimately, the aircraft require ships to operate from.

Threat Axis.  Unlike the aerial threat, submarine threat axes are much more limited and are primarily centered around the course of the advancing HVU.  Subs that are significantly offset from the course of advance will be unable to achieve a viable intercept position without significantly increasing speed and making their presence known.  Thus, while a few flank and rear ASW escorts are needed, the majority can be concentrated along the forward arc of the direction of travel.

Electronic Warfare (EW) Escort

We should have a few dedicated EW escorts.  Our current ships are limited to small, underpowered SLQ-32 / SEWIP components that are designed to provide self-defense, only.   A dedicated, high powered area defense EW ship is needed that can operate antennae as large as needed and as many as needed along with numerous, high powered transmitters for jamming.  Think of this as the EW version of Aegis.

We use dedicated, large EW aircraft so why not ships?  Compare the size of even aircraft EW equipment to ship EW equipment and it becomes immediately obvious how meager our shipboard EW is.

Attrition

Another factor in escort number determination is attrition.  Some extra escorts are necessary to allow for possible losses.  Without some extra escorts, the entire group would be forced to retire upon the first loss of an escort.

Escort Concept

Having considered the above requirements, let’s see if we can bring it all together and conceptualize an escort requirement.  We’d like to have multiple defensive rings similar to the following:

Escort Concept
Defensive Ring	Radial Distance, miles	No. of Escorts	Purpose
Inner	1	4	engage leakers
Second	20	18a	main engagement zone
Third	35	8b	early warning / early engagement
Fourth	60	8c	ASW / early warning

^a each ship covers a 20 deg sector

^b each ship covers a 45 deg sector
^c ships spread across 45 deg arc on course of advance

This gives us three engagement zones plus a distant ASW zone using a total of 38 escorts.  Most of you will be stunned at the number but it’s an historically and analytically supported requirement.  We’ve just forgotten how many ships are needed to form a survivable, defensible group. 

Another aspect that leads to larger escort requirements today is the increased range and speed of attacking weapons (aircraft and missiles).  In WWII, aircraft had to basically overfly the target ship to release weapons and their speed of approach was only around two hundred miles per hour which provided extended engagement windows (time) for the defenders.  With today’s weapon’s range and speed and the resulting short engagement windows, the only compensation is to engage further out and with more escorts.

This immediately leads one to wonder why the Navy never exercises with this kind of escort density.  Hey, it’s peacetime – I get it.  There’s no need to provide that level of escort on a routine, peacetime basis.  But, shouldn’t we be exercising this escort concept on a regular basis so that we know how to do it when war comes?  I guarantee you that none of our current admirals or captains have the slightest idea how to manage a wartime escort group, where to place the escorts, what tactics to use, or how to maneuver a large, spread out group. 

Consider the ASW escort challenge …  What will the rest of the group do if a submarine is detected?  Keep going?  Turn away?  How many escorts should engage?  Can we afford to detach escorts for prosecution of the target?  How do we compensate if we detach escorts?  This is the tactical level of control that none of our naval officers have any grasp of and never will since we don’t practice it.  We’re going to wind up learning the hard way when war comes and the price of that learning will be sunk ships and lost crews all because the Navy refuses to conduct serious combat exercises now, during peacetime.

Note that the above only applies to a single HVU or a closely clustered group of HVUs.  For a wartime group of 4 carriers, the carriers themselves will be separated by 5-10 miles so the size of the defensive rings and the number of escorts would have to be adjusted accordingly – something we should be learning about in exercises but aren’t.

We also have to make adjustments for reality.  While we might like to have thirty or fifty or hundred escorts, if we only have, say, 15 available then we have to modify our thinking.  Part of that modification might be to cancel missions that have inadequate escort availability.  Alternatively, we might have to sail with lesser numbers of escorts.  How do we adjust?  Where do we place our limited escorts?  How does inadequate numbers affect our tactical usage of the escorts?  These are the types of scenarios we should be exercising and learning, now, during peacetime, instead of wasting our time on useless deployments to show the flag or chase pirates in skiffs.  We are wasting this valuable peacetime.

Fletcher Class Destroyer

Finally, let’s compare our potential existing escort strength to the conceptual needs we’ve just described.  We have around 80 Burkes/Ticos so we can fill out two task forces – and that’s before we’ve lost any ships to combat.  Are two task forces enough to conduct a peer war?  I don’t think so.  Compare that to WWII when we built 175 Fletcher class destroyers, alone, and many dozens of cruisers and battleships.  Of course, we also had hundreds of older destroyers and destroyer escorts and, as the war went on, another hundred or so of newer Sumner/Gearing class destroyers.  We’re not even close to that level, currently, nor should we be.  We didn’t have all those ships when WWII started.  We built them rapidly as the war progressed.  The problem is that we no longer have the ability to rapidly build up ship numbers.  We lack the shipyards, the work force, and, worse, our designs have become so complex that it requires years to build a single Burke class destroyer.  We absolutely need to revisit our entire warship design philosophy with an eye towards simplifying it for rapid mass production.

All right, there you have it.  You now understand the role of escort ships and you have some idea of how many are needed and how they should be used.  For the Navy, it’s now time to start exercising these concepts and finding out what works and what changes need to be made.  We also need to start developing combat commanders who have actual command experience with large escort groups.  Peacetime is a precious commodity – it’s the time to prepare for war and we’re squandering it with worthless deployments, pirate chases, and flag waving.

_________________________________

(1)Wikipedia, “Fast Carrier Task Force”, retrieved 4-May-2020,

https://en.wikipedia.org/wiki/Fast_Carrier_Task_Force