Hunter-Killer ASW Groups

In WWII, with the exception of a few very fast transports that traveled alone, protected by their speed, most supply ships made the Atlantic crossing in convoys.  Protection was provided by escort ships.  Threats to the convoys included air attacks, notably from Focke-Wulf FW 200 Condor long range bombers, surface ship attacks, though this was more of a potential threat than actual, and U-boats which nearly choked off supplies to Britain and, later, Russia.

While the convoys had ASW-capable escorts, they were only marginally effective.  The major problem was that they were tied to the convoy.  They could not detach from convoy to conduct long, drawn out ASW engagements.  After a brief counterattack against a submarine, the escorts had to quickly return to their place in the escort screen.  Unfortunately, effective ASW generally involved patience and time that the escorts didn’t have.  The role of the escort ships was to hinder submarine attacks by their presence rather than kill submarines.

One of the solutions to this inability to engage submarines on a protracted basis was the formation of dedicated anti-submarine (ASW) hunter-killer (H-K) groups.  These groups were formed around smaller escort carriers along with several destroyers, frigates, destroyer escorts, corvettes, and sloops.  Not being tied to a convoy, the H-K groups were able to move independently, hunt for submarines rather than just react to an attack, and take the time necessary to prosecute contacts.

The H-K escort ships were, by and large, lower capability or second line vessels such as Black Swan class corvettes, River class frigates, Wickes and Clemson class 4-stack destroyers, and the like.  ASW, at the time, did not require state of art ships because the ASW sensors were small in size and the weapons were common.  The main requirement – the main ‘weapon’ - for effective ASW was persistent presence – the ability to patiently search and remain engaged as long as necessary, using the submarine’s limited underwater time against it. 

The most successful US ASW escort carrier was USS Bogue (CVE-9) whose aircraft and escorts sank 11 German and 2 Japanese submarines.  The carrier’s aircraft were Grumman Avengers and Wildcats which used depth charges, rockets, and Mk24 FIDO acoustic homing torpedoes.

USS Bogue with TBM/F Avengers on Deck

This also raises the issue of weapons.  The major difficulty in WWII ASW was the lack of weapons that could effectively engage a submarine.  Even with the nascent sonar systems of the time, detection was relatively easy.  The problem was that the weapons of the time were very inaccurate and largely ineffective.  It required many weapon launches to achieve a kill and many submarines got away despite the profligate expenditure of weapons.  Depth charges, the main weapon of the time, were marginally effective, at best.

When WWII ended, the US Navy continued to operate H-K groups culminating in the Cold War ASW skirmishes with the Soviet Union submarine fleet.  Due to the larger size of the ASW aircraft, larger carriers were required and the Navy converted WWII Essex class carriers to dedicated ASW carriers.  Surface ships employed ASW weapons such as Weapon Alpha, hedgehogs, torpedoes, and the unmanned DASH helicopter.  Groups consisted of a carrier and 8 destroyer escorts.

USS Essex, CVS-9, with S2F Trackers on Deck, 1965

Eventually, as the ASW Essex carriers retired without replacement and long range land based ASW patrol aircraft came on line, the H-K concept died out.  ASW efforts became centered on the S-3 Viking fixed wing ASW aircraft operated from carriers, land based ASW P-3 Orions and the like, and SSN submarines.

Of course, the S-3 Viking has been retired without replacement.  Land based ASW aircraft require a permissive environment to operate and that is an unlikely scenario in a peer war.  Submarines, while effective in the ASW role, will be tasked with many missions and their ASW efforts will be somewhat sporadic.  Worse, they will be unable to operate near friendly units due to the inability of those units to distinguish friend from enemy.

Thus, the Navy currently has no H-K groups and little in the way of persistent, dedicated, effective ASW capability.  Ironically and dangerously, while our ASW capability is withering we are simultaneously seeing the rise of peer Chinese and Russia submarine fleets.  While neither yet presents an overwhelming threat, the trend in both numbers and quality of submarines is improving and it is only a matter of time until the submarine threats become substantial.  Further, many smaller countries are investing in quiet, deadly, conventionally powered submarines (SSK) which present a major threat to our nearer-shore naval operations.

What conclusions and lessons can we draw from the history of H-K groups?

• Combating submarines at the convoy is a losing proposition due to the escort’s inability to take the time necessary to successfully prosecute a contact.
• Aircraft are extremely useful and effective ASW platforms.
• Persistence and patience are the key attributes of ASW
• Land based, ASW patrol planes do not have the persistence necessary for truly effective ASW engagements.
• State of the art ships are not necessary.  The ASW gear must be reasonably modern but the ships themselves do not need to be front line vessels.

So, what does all this tell us about potential modern H-K groups?

Need - Having noted that the convoy is not the place to attempt ASW and that convoy escorts make ineffective submarine killers, it is clear that modern H-K groups, acting independently, are required.

Aircraft – While a fixed wing aircraft would be ideal for a H-K group, the reality is that rotary wing (helo) aircraft are the better choice in terms of simplicity and ease of operations and budget.  An S-3 Viking type aircraft would require a carrier with catapults, arresting gear, advanced maintenance support, etc.  In contrast, helos can operate from any flat surface which lends itself to modified commercial vessels similar to the simplistic escort carriers of WWII. 

Ships – As was found in WWII, the best combination of ships for an H-K group is a carrier and several low end ASW corvette/destroyer escort type vessels.  ASW does not require state of the art ships with advanced radars, stealth, etc.  A basic, cheap ship that can carry sonars, arrays, and anti-submarine weapons is all that is needed.  The baseness and cheapness of such ships allows them to be procured in numbers and put at risk.  Does anyone really think we’re going to risk $2.5B Burkes playing tag with submarines?  Heck, it would be foolish to put the Navy’s new $1.5B frigates at risk.  After all, ASW is a high risk business and the submarine has most of the advantages.

Regarding the carrier, a modified commercial cargo/tanker vessel would be suitable.  Add a flight deck with enough room to operate around 10 MH-60R helos and a covered hangar for maintenance and call it a day.  Simple, cheap, expendable.

What we absolutely can’t do is what the Navy always does: build a gold plated, do-everything ship.  An ASW carrier is, by definition and requirement, a low end ship in a high risk job.  That calls for a cheap, expendable (another way of saying cheap) ship that we’re willing to send into harm’s way.

Weapons – We now have ASW weapons (torpedoes) that we believe are effective – at least, that’s what we tell ourselves.  However, to the best of my knowledge, they have never been tested under realistic conditions.  As DOT&E has noted many times, the Navy’s submarine threat surrogates are unrealistic and unrepresentative in the extreme and testing has not occurred under operationally realistic conditions.  We need to fire actual torpedoes (warheads removed, of course) at real submarines that are trying their best to survive and see what happens.  Yes, we may dent some propellers and cause some superficial damage to the submarines (assuming we can hit them!) but that is well worth the cost to find out how effective our weapons and tactics really are.

I’ve stated repeatedly that we need a Soviet RBU-ish type of rocket depth charge launcher (see, "The Modern Hedgehog").  This is even more important for H-K corvettes that will go toe-to-toe with submarines.

The US Navy has all but abandoned ASW in any persistent, dedicated, effective form and we need to regain that capability.  We need to bring back a fixed wing carrier ASW aircraft, ASW corvettes, and dedicated ASW Hunter-Killer groups.