The Large ASW Ship

In the process of studying ASW systems during the war (yes, I now have a very long, detailed article on these almost done) I thought up an idea that I don't think anyone actually tried during the war but, would likely have been a valuable weapon against subs in convoy actions. That is, the large ASW ship.

This ship would (by my design) have been about the size of a pre-dreadnought battleship say about 400 feet in length with a beam of about 50 to 60 feet and displacing about 9,000 tons give or take.
This ship would have had two VTE engines with a top speed of about 18 knots. The hull would include a fairly deep torpedo defense system along most of the length.
Armament would have been:

6 10 to 12" 25 to 30 caliber guns in two triple turrets. But, these guns wouldn't be firing common shells or AP rounds. Rather they would have higher elevation (to about 45 - 50 degrees) and fire an anti-submarine shell at lower velocity. Sort of a super-Limbo / Squid that could be fired effectively to about 20,000 yards. The turrets would have light armor, say 1" or so mostly for blast protection of the crew.
200 RPG would be carried and loading arrangements would allow about 2 rpm max or a 3 round salvo every 15 to 30 seconds.
The secondary armament would be 4 x 6" pedistal mount barbette guns for self-defense and surface actions. Again, splinter armor of about 1" would be provided. These would be in broadside mounts.
An AA armament of 2 twin 4" HA mounts and 2 quadruple pom poms along with an odd half dozen or so 20mm would be mounted.
In addition to the main armament about 50 to 80 depth charges would be carried with two stern racks and 4 K guns.
A single above water stern mounted "torpedo tube" would be installed to fire Mk X one ton depth charges with 6 to 10 of these carried.
A large two plane + aircraft hanger and awtharthship catapult would be included. The plane could be used to assist in ASW work with depth charges or sonobouys or, alternately a fighter-like float plane or two could be carried to assist in shooing off German recon planes.

2 sonars and a suite of suitable radar and ESM would be carried as well.

The idea for this ship is that one is included in the escort and stationed such that it can support attacks by other escorts on a submarine target. With a 20,000 yard firing range such a ship could deliver multiple Limbo / Squid-like attacks on a target from quite a distance while a smaller escort closed with the contact. The big ASW ship could use range and bearing data from the other escorts to plot firing coordiantes as well as use its own sonar when possible to gather data.
With turreted ASW weapons 360 degree fire is possible. With a salvo in the water every say, 30 seconds such a ship could lay down a seriously large depth charge pattern up to 10 nm from its location. This would give two additional advantages:

First a sub such engaged would have little or no warning of the impending attack. Its first warning would be the shells entering the water. This gives a reduced time to maneuver between attack and impact increasing the likelihood of success.

Second, the engagement time would be greatly reduced. This ship could be firing on a contact miles distant within a minute or two after detection (assuming the guns are manned for action).

It also provides some air cover even when an escort carrier isn't present. It could also provide starshell instead of a small escort having a larger ammunition capacity and, it provides a bit more surface defense to the convoy than small escorts could.

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The question I would have is how would it compare in price to a CVE? While the CVE might not be as effective at night or in bad weather at other times it's got a better range by an order of magnitude.

 

IMO a CVE would be a lot more cost effective, but I wonder what the end result would look like, I immagine a cross between a Terror and a Deutchland .

Acquiring a sub at 20.000 yards with 1940 technology is a freak occurrence, designing an expensive ship optimized for thar sort of engagement doesn't look like a great idea (the sort of gun you envision will not fit on converted merchant hulls, especially with a triple mount).

With a low velocity large caliber gun that fires depth charges , the depth charge would still need to be designed so as to resist gun tube accelleration at the expense of it's other performance, a rocket is a much more sensible delivery system. The only advantage of the gun is the smaller shell weight/greater ammo load, but IMO the much ligter weight of the weapon more than makes up for that. In the end to be practical your "gun" would need to be .... a breech loaded mortar.

After the war when the massive numbers of soviet Whiskey subs were considered a major threat, and funds for ASW were rather plentiful, nobody came up with something like that.

Some post war solutions to engage a sub that had been acquired at long range were:
- Improved ASW mortars (but AFAIK none had more than 1000m range)
- Rocket based delivery systems for both smart (Ikara and ASROC) or dumb ordonace (the various soviet ASW rocket launchers).
- Radio controlled drones (DASH)

And of course the ASW helicopter that is still the preferred one today.

ASW tactics mostly uses a hunter/killer combination, AFAIK this is because sonar performance deteriorates badly with ship speed, especially for surface ships, so having the same platform do targetting and weapon delivery is difficult, one large platform is not worth two smaller ones.

I also believe it makes no sense to have a naval gun with more than 45 degrees elevation unless you plan for AA use, for a given muzzle velocity and shell shape 45 will give you maximum range.

 

I hope you publish your article on this Forum, I guess it will be an interesting read.

When using smaller escorts you can afford loosing a vessel or two and still have sufficient defense to push through.

To base the defense of a convoy on one large ASW may be fatal. If the large ASW should suffer technical problems like for example a breakdown in the propulsion system or getting crippled by a torpedo hit at the stern section damaging the propellers or the rudder (like the Bismarck), the convoy would virtually be without means to defend itself, unless of course you have a lot of smaller escorts available. But on the other hand, then there will be no need for a large ASW.

When you mention protection against torpedoes I assume you think of a belt of hardened steel applied to the hull? To survive a hit or two from a torpedo you need approximately 10 to 12 inches of reinforcement.
In this context a ship of 9000 tons displacement is not a very large vessel. When you attach such an amount of extra weight on a vessel of this size you will get a 'wet' ship. She will lie low in the water and the seas will constantly wash over her main deck. Being semi-submerged in the icy waters of the North Atlantic you will face problems from icing, reducing her efficiency. The crew will have a tough time keeping her fit for fight all the time.

 

Pretty much.

The ship doesn't have to. Instead, it utilizes what would be the equivalent of a forward observer (another small ASW vessel) to direct the fire. This is certainly possible against targets ashore and could be done against a sub in much the same way. That is, the ship takes a range and bearing off of the directing ship and possibly some other ships it has good data on with regard to relative position and then plots the sonar contact from range and bearing data the other ship provides.
Being able to lay down a patten of say anywhere from 3 to 12+ rounds in a matter of minutes would aleviate some of the inherent inaccuracy that would come with range and use of indirect data.

The guns would be much like breech loading mortars or, more like low velocity howitzers as both charge and elevation could be adjusted for range. The shell would be similar to a thin wall high capacity HE round only with a blunt, flat nose and a windscreen that would come off on impacting the water. This way the round stops forward motion on hitting the water and sinks. A conventional hydrostatic fuze arrangement would be used.

Actually, the US did. This was the Mitscher class or even more precisely matching the Norfolk CLK 1 anti-submarine light cruiser. The weapon that replaces my design is Weapon Alpha. This is a rocket propelled depth charge fired (theoretically) at up to 40 rpm. What over took the design and weapons like Squid, Weapon Alpha and, other depth charge-like ones is that subs got faster and deeper diving than an unguided weapon system could reasonably handle. Thus, the switch to high speed guided homing torpedoes.

A ship possessing a depth charge-like weapon capable of projecting fire to a distance is possible with WW 2 sonar technology if the navy(s) involved recognize that integrating the escort's ability to share information is utilized. Even the use of a spotting plane from the large ASW ship could be used to direct fire. Hence my inclusion of capacity for a float plane or two on board.

But, all ended up going to deliver a homing torpedo. ASROC and helicopters just make it possible to get the torpedo near the sub faster than launching it from the ship itself. The weapon I proposed does roughly the same thing but with a depth charge-like weaon similar to Weapon Alpha or the Soviet era RBU launchers. The difference is that it is gun based rather than rocket based. But, in 1939 - 40 rocket technology isn't up to throwing a 500 to 800 lbs payload to 10 to 20,000 yards. Guns are.

Here, the larger ship doesn't bother to close into close action with the sub but rather stands off and attacks as directed by the smaller ASW escort. The advantage is that the large platform could be firing on two targets at once or, could engage a target far faster than a second escort that had to steam several miles, then aquire the target and, then act over time against it.

It does if you want high arching fire at close ranges as the intended use of this weapon requires a short minimum range too. But, for the most part 45 degrees would have sufficed.

 

I'd forgotten about Weapon Alpha but AFAIK it was a rocket system with a range of around 1000 m so the SQUID ASW mortar is the closest I can find to your intended gun and while it doesn't require an 8000t ship it does have only a 1000m range.

What you are suggesting is essentially a "killer" component of a hunter/killer pair that relies on other platforms for acquisition.
For this the biggest advantage of using a gun is the long range and high magazine capacity, you need at least 10000m range to justify the platform as it needs to be able to deliver the depth charges further than the ASW weapons of the "hunter" that is closer to the target and likely to have some a more conventional forward firing ASW weapon with a 200 to 1000m range.

She still looks very expensive compared to a couple or trio of conventional escorts or a CVE, her fire control would need to be BB class and that's not cheap, also the effort of designing the new gun is a high initial capital cost, though it's actual production cost is going to be closer to field gun than to the horribly expensive big naval guns. Thinking of that would adapting one of the larger field howitzers like the US 240mm do? it could certainly cut costs drastically compared to designing a new gun, you already have your 20 Km range and you can probably get a decent depth charge with 160Kg even if it needs to be thicker cased than optimum.

The capability of delivering a depth charge salvo anywhere within 15 km of the convoy in any weather (or at least any weather where the sub would be able to operate) is very interesting as can make for a lot of "mission kills" as the probable reaction of the sub would be to dive deep and so loose contact with the convoy.

I would definetly not go for a secondary/tertiary battery arrangement, if you are thinking US the 127 DP is more than enough against any sub and even the British 4" AA will be sufficient, the 5.25 of the Dido and KGV is overkill, AFAIK Hunt class DE could effectively deal with a surfaced sub and if you have the misfortune of running into a big surface raider a four gun 6" battery is not going to help much, having some AP shells for your main guns is a lot more effective, a few large caliber shells can probably convince a Lutzow or Hipper to look for easier prey.

 

Sort of modernize the USS Vesuvius and you might be close. See
USS Vesuvius (1888) - Wikipedia, the free encyclopedia

 

I was thinking on the main battery simply using rebored older guns that were obsolete in their original role. A 8 to 9" gun or 10" bored out and shortened in caliber, if necessary. The same was being applied to the other armament. Use off-the-shelf obsolesent stuff. For a US version some 5"/51s and 5"/25 cal AA guns.
The fire controls could be older stuff replaced on either cruisers or BB with the necessary gear changes for ballistic differences in the weapons.
This ship doesn't really require top of the line anything really but rather could be built on the cheap.

 

I bet the sailors on the freighters would be happy to know that the defense of the convoy depends on obsolete, second hand equipment.

A german submarine type VIIC/41 approaching a convoy 10 nm away is a fairly small target. Using obsolete conventional armament and fire controls, the chances of hitting this object is zero.

From what I learned in the ordnance corps (almost 40 years ago), hydrostatic fuses are sensitive devices.
Using conventional guns and HE shells you have two options:
impact fuses or time delay fuses.
The impact fuse will probably detonate when it hits the water surface, or if it is less sensitive, the sub if it hits it at all.
The time delay fuse you can set at an approximate time calculated from the sub's position, but since the sub will be moving this calculation will be wrong and the detonation will cause no harm to the sub.

In this combination of obsolete equipment and inaccuracy, most of the freighters will be sunk and million of dollars worth of equipment will be lost due to ignorance.

 

I wasn't suggesting the ship be devoid of fire controls or that they should be inadequite. But, for example an older US mk 3 set off a cruiser that got replaced with a mk 8 set would be more than adequite and a far cry better than the telescopic sights of a deck gun on a U-boat.

As for fuzing, if the Allies could figure out how to make a VT fuze work with tubes in it they should have no problem devising a hydrostatic one. But, a time delay would work too. All that need be determined is the sink rate of the round with its impact on the water initating the fuze action.
Either way, fuzing isn't a major problem here.

The guns suggested by the way are not obsolete for this purpose. They are obsolesent for their original purpose in fighting other major surface combatants. A sub does not fall into this category. It is a torpedo boat that can submerge. On the surface it is an egg shell with a hammer.

 

To be effective would you need a class of 4 to 8 ships to have enough available to meet convoy needs? Are there enough obsolete guns to arm this many ships?

Would it be wise to have so important an ASW asset motionless while it recovers it's seaplanes?

In real life how often did ships engage two different targets with it's main armament?

New turrets, rebored guns, new fuses, plus new tactics seem alot to try and perfect in a short time frame. Then there is the problem of getting past "gun" and "plane" admirals who could look at a CVE or DE as a vessel that could preform ASW AND conventional combat operations.

 

Yes, lots. They most often ended up being scrapped or turned into coast defense weapons. And, yes, you would need to build a number of them but any particular convoy would only need one.

Ships don't need to stop to recover float planes. They can do it while slowly steaming. In fact, the recommended method was for the ship to turn into the wind and waves and then the seaplane or float plane would land in the wake which would be smoothed out by the ship's motion. The plane then taxis up to the ship and the crew lower a hook on a crane that the observer on the float plane would attach to it while the pilot maintained station on the ship matching its speed. Once hooked up the pilot would wait until the crane started to lift and then cut the engine.

All the time. That was what the guns were for.

There likely would be problems. But, the tactics really are not new. It is just the target is. Firing a ASW round from a gun is no different than firing any other round. The targetting procedure is unchanged too. So what if the target is submerged. So long as the rounds enter the water at the right point they would do the job just like bracketing a surface target.

 

Are you envisioning a completely new ship from the keel on up or are you thinking of taking a existing hull design like a British "Town" class hull?

 

I was envisioning something more along the lines of a WW 2 monitor with a bit more freeboard built from the keel up. Ships of this sort with only a limited plant (VTE with moderate speed) are not too hard or costly to build. Since it would have no armor other than splinter armor there is little problem with materials. Plate steel for ship building is plentiful.

 

Why not just modernise the Vesuvias's main armament. Not a great deal of range but a pretty good "close enough" factor and I suspect you could out range most torpedos. Could probably fit on to many merhant hulls and they could still carry some cargo.

 

T.A., I think you are asking too much from the hull you propose. Looking at pre-dreadnought and early dreadnoght class ships, they had beams of 74' to 83' feet ( IJN Satsuma-83', IJN Mikasa 78', HMS Ocean-74' ). As for the WWII era monitors HMS Erebus-88' and HMS Roberts-89'. This was with 2 gun turrets only. In modern ships with triple gun turrets- Deutschland 71', Alaska/Sharnhorst over 90', but this is with modern gun design. With a beam of 50 to 60 feet, it does not seem feasable to place a triple gun turret with 10" to 12" guns.

You run into greater problems on your length. HMS Erebus ( WWI vintage monitor ) is 405' in lenght, HMS Roberts ( WWII vintage ) is 373' in length. Both classes served in WWII. The hitch is that they could only manage a single turret forward, with the superstructer/funnel/secondary/AA guns aft. On a 400' foot deck it would be difficult to place a second turret, let alone depth charges/K-guns and catapult/hanger for a seaplane.

To comprise all the elements you want, you seem to need a hull with a beam of 65' to 70' and a lenghth of 600'. A Deutschland class (610' x 71) not only fills the bill, it looks the part. Alas, the kreigsmarine would be unkilely to consider selling them.

All is not lost! the Kent series of the County class crusier would do nicely. 630' long with a beam of 68'. It comes with a floatplane, and a lower afterdeck for depth charge racks. with plenty of room for K-guns and secondary/AA guns. Built in the 20's, they were old Treaty cruisers and all ready long in the tooth. With 7 ships in the class there are plenty of ships to convert.

Keeping thier speed they make true Hunter-Killers. If as TiredOldSoldier suggests you use 8" guns, you could use the original turret layout and add 2 more guns for a wider pattern.

To be honest a CVE could do all you really ask of your large asw except depth charge, and could do it much farther out.

 

Well Vesuvius mounted 3 15" guns (not in turrets though) on a 930 ton hull. Range was rather short but it was built in 1888 so technology should be able to improve it quite a bit. See:
http://en.wikipedia.org/wiki/USS_Vesuvius_(1888)

 

I think you would need a time machine first as USS Vesuvius was struck in 1922 and scrapped, otherwise a first class idea.

 

The plans must still have existed and a pnumatic cannon doesn't need anywhere near the strength of a gun powder one. I'm pretty sure the ones used in the current pumpkin chucking contest get ranges on the order of a mile or two and they are limited for the most part to the strength of the pumpkin.