Atlantic Convoy Escort

Why were the US and Allies somewhat late in the application of jeep carriers, antisub frigates and long range patrol bombers escorting supply convoys across the Atlantic?
The U-boats had a field day in the beginning since there were nothing to oppose them but the odds turned against them as soon as anit-sub ships started escorting convoys.

 

Late or slow? The U-boat threat "ermerged" over time, wasn't like it was nothing then boats being sunk all over the place. Several "techniques" were adopted as a quick measure to try to maximise safety.
The advent of ASDIC, particularly on nimble destroyers was a game changer, also the merchants arming themselves (which took the guns, placing them, training crews - time in other words) meant that U-boats could no longer attack from the surface, and could no longer hide under the waves. ASDIC took time to invent and develop. I thougt they tackled the BIG problem pretty quickly, and came up with effective countermeasures, that made the submariners life a living hell. Long range bombers had to be found, crews trained and effective weapons and attack techniques developed. With practice, the air crews got better and better, until they became outright deadly to a u-boat caught with its pants down.
Theres always a golden period when a new "weapon" is deployed - liewise there is always a lag for the countermeasure to emerge.

 

The short answer is development, ship building schedules, and interwar fleet doctrine. No power built a particularly good ASW capability between the wars. Britain was in better shape than almost anyone else in terms of escorts, actually, but they were still in quite short supply at the outset of the war. If my notes are correct, in 1939 the RN had somewhat less than 200 destroyers and a tiny handful of sloops and minesweepers adequate for ASW duty. Less than 300 escorts all told, and probably less than 250. And many of those were needed for fleet escort duty. The ubiquitous Flowers were as yet unbuilt. (The first order came in the 1939 building program.)

The potential of aircraft as a significant submarine deterrent was seen pretty early on, but aircraft range was still somewhat limited, navigation over water was hazardous, and flight decks were few and very precious. Aircraft were limited to their "combat radius", which was usually little more than five hundred miles. (A long legged aircraft might have a range of 2000 miles. Divide that by two and take out a safety factor of . . . lets say 25% for loiter time and combat maneuver, and you end up with a practical range of little more than seven hundred miles. And if you're in doubt, remember that even mid war heavy bombers landed in Greenland to refuel on ferry missions, which is why we can dig a B-17 out of the ice there every now and then.) Which leaves the infamous mid ocean gap.

At the outset of the war the RN briefly tried to use fleet carriers in an ASW role. In 1939 they had seven flight decks. When Courageous was sunk by U-29 within weeks of the beginning of her mission (and just days after Ark Royal had a very close call on a similar mission) that spelled a temporary end to CV ASW duty. The widespread use of carriers in ASW would need to wait for the availability of large numbers of inexpensive flight decks. The first "CVE" conversions (Audacity and Long Island) began to appear only in 1941. Not until 1943 were there enough flight decks to regularly spare them from fleet duty to participate in active Mid-Atlantic ASW. (The first Bogues commissioned in September of 1942, and Bogue was AVG-6. Which is to say quite early.)

It's possible that interwar programs could have been altered to anticipate the ASW need, but escort carriers, due to their slow speed, were reliant on catapults for effective operation. Hydraulic catapults were still somewhat immature in the thirties. (Lexington and Saratoga were both built with monstrous flywheel catapults that were removed and replaced in an early refit. Early war Japanese carriers dispensed with catapults altogether.) And building escort carriers large enough and fast enough for rolling takeoffs defeats the purpose as it raises the cost and limits the numbers you can build, without really making them any more useful as ASW platforms or any less vulnerable to their prey. It would probably have been difficult or impossible to bring the cost of "economy" carriers down sufficiently to make them effective ASW platforms much before 1940.

And lest you find too much fault with RN interwar building programs, it's worth remembering that all the ASW capable ships in the world would have been a moot point if the RN hadn't been able to contain Germany's surface combatants. The ultimate problem the Royal Navy faced was simply building up after an extended period of austerity. There simply weren't enough ships of any type to contain all threats in all theatres.

 

The one area where the Western Allies did drag thier feet was the employment of Long Range and Very Long Range aicraft for anti-sub work. Basicly neither Bomber command (RAF-USAAF) were keen to give up the aircraft they saw as needed to prosecute the Strategic Bombing campaign, and it took pressure from on high to free these assets up.

 

That doesn't surprise me somehow. There was a "strategic bombing will win it all" mentality in both air arms. Along with the old mantra "the bomber will always get through." In the end I think it's more accurate to say that the side with air superiority will win, but the importance of strategic bombing was at the time much exaggerated at the expense of other air missions.

 

Pretty good answer SP, but the RN actually had about 100 - 120 (edit: 225) ASW ships of various types, as they had a large number of ASW trawlers in 1939. I would actually say that Britain did have a pretty good ASW capability in 1939, certainly far better than any other nation. In addition, they had planned to use mines to prevent U-boats from getting through the channel, which proved very effective at both sinking U-boats and reducing their effectiveness by forcing them 1,000's of miles around Scotland to get into the Atlantic. Keep in mind that Germany only had 57 U-boats at the outbreak of war, and built about 58 more in 39 & 40. Meanwhile the RN ordered 145 Flower class escorts in 1939.
Of these 57 U-boats operational Sep 1 1939, only 31 were of the type I, VII & type IX that could venture into the Mid-Atlantic gap, so the 200 odd RN destroyers & 100+ ASW ships is a pretty good number. Of the remaining 26 U-boats operational Sep 1939, 8 - 12 were used as training boats, the other 16 or so were smaller coastal boats, used only in the Baltic, Med or North Sea

Where did you get the idea that there was "nothing to oppose them" in the "beginning"? This is actually quite wrong, although if you are talking about the beginning of the US war in 1941 you are correct. Why was the US so poorly prepared, even after WWII had been raging for 2 years and subs had proved such a deadly menace? I dunno, poor planning & crappy leadership comes to mind... (to be blunt)

Now, as to your "The U-boats had a field day in the beginning since there were nothing to opposethem", lets review some facts:

For the first 3 months of "Operation Drumbeat" a grand total of zero U-boats were sunk in US (& caribbean) waters, and in the first 6 months following Pearl Harbour, there were only two U-boats sunk in these waters.

Now, how did the Royal Navy do at ASW during the first 6 months of the European war?

Lets look at those 31 (+1) U-boats of type I, VII & type IX available in 1939:

Type I: 2 boats, U 25 & 26
Type VIIa: 10 boats, U27 - U36
Type VIIb 11 boats, U45 - U55
Type IXa 8 boats U 37 - U44
Type IXb 1 boat, U-64 (commissioned Dec 16 1939)

U-27: Sunk 20 Sept, 1939 west of Scotland, in position 58.35N, 09.02W, by depth charges from the British destroyers HMS Fortune and HMS Forester. 38 survivors (no casualties).

U-33: Sunk 12 Feb, 1940 in the Firth of Clyde, in position 55.25N, 05.07W, by depth charges from the British minesweeper HMS Gleaner. 25 dead and 17 survivors.

U-35: Sunk 29 Nov, 1939 in North Sea, in position 60.53N, 02.47E, by depth charges from the British destroyers HMS Kingston, HMS Icarus and HMS Kashmir. 43 survivors (no casualties).

U-36: Sunk 4 Dec, 1939 in the North Sea south-west of Kristiansand, in position 57.00N, 05.20E, by a torpedo from the British submarine HMS Salmon. 40 dead (all hands lost).

U-45: Sunk 14 Oct 1939 south-west of Ireland, in position 50.58N, 12.57W, by depth charges from the British destroyers HMS Inglefield, HMS Ivanhoe and HMS Intrepid. 38 dead (all hands lost).

U-53: Sunk 23 Feb, 1940 in the North Sea in the mid Orkneys, in position 60.32N, 06.14W, by depth charges from the British destroyer HMS Gurkha. 42 dead (all hands lost).

U-54: Missing since 20 Feb, 1940 in North Sea, position unknown, probably lost to a mine. 41 dead (all hands lost). (FDS/NHB, June 1983).

U-55: Sunk 30 Jan, 1940 south-west of the Isles of Scilly (English Channel), in position 48.37N, 07.48W, by depth charges from the British destroyer HMS Whitshed, the British sloop HMS Fowey the French destroyers Valmy and Guépard, and by depth charges from a British Sunderland aircraft (228 Sqdn.). 1 dead and 41 survivors.

U-39: Sunk 14 Sept, 1939 north-west of Ireland, in position 58.32N, 11.49W, by depth charges from the British destroyers HMS Faulknor, HMS Foxhound and HMS Firedrake. 44 survivors (no casualties).

U-40: Sunk 13 Oct, 1939 in the English Channel, in position 50.41,6N, 00.15,1E, by mines. 45 dead and 3 survivors.

U-41: Sunk 5 Feb, 1940 south of Ireland, in position 49.20N, 10.04W, by depth charges from the British destroyer HMS Antelope. 49 dead (all hands lost).

U-42: Sunk 13 Oct, 1939 south-west of Ireland, in position 49.12N, 16.00W, by depth charges from the British destroyers HMS Imogen and HMS Ilex. 26 dead and 20 survivors.

In addition, 8 more of these U-boats were lost between Mar 1940 - Aug 1940: U-25, U-26, U-31, U-32, U-44, U-50, U-51, U-64

(All this data from Uboat.net The U-boat Wars 1939-1945 (Kriegsmarine) and 1914-1918 (Kaiserliche Marine) and Allied Warships of WWII - uboat.net an excellent U-boat refernce site)


So to sum up, of those 32 German long range type I, VII & IX operational by the end of 1939, the British sank 12 of those in the first 6 months, and 20 (62.5%) had been sunk in the first year of the war. (not including sinkings of smaller coastal boats)

Actually pretty damn effective I think!

 

Sorry, Freebird. Missed the trawlers. But if you look at my estimate, I was guessing maybe 250 ASW capable escorts. (After all, they had about 200 destroyers.) So I was guessing from somewhat inadequate information (Janes and Wikipedia) that they had maybe another 50 to perhaps 100 ASW capable escorts in 39. In light of your information my estimate was probably somewhat low, but I'd still contend that they were spread pretty thin. The very stopgap nature of programs like the Flower class would seem to confirm that Whitehall, at least, believed that they needed more. Even assuming they had as many as 400 ASW vessels, keep in mind the sheer volume of shipping they needed to protect.

So here's my estimate of RN commitments at the outset of WWII:

Convoy escort in the Atlantic, and Mediterranean.
Fleet and task force escort for forces in the Atlantic, Indian, and Pacific oceans and the Mediterranean Sea.

I'd guess you'd want separate escort forces available for at least the following:

Western Approaches (You'll want to patrol this key area at all times to suppress U-boats that might otherwise loiter here.)
The Channel (See above)
Canadian Coastal Escort
Atlantic Escort
Gibraltar/Mediterranean Convoy Escort
Scapa
Gibraltar
Alexandria
Eastern Fleet

So we're now dividing that pool of ASW escorts into at least 9 buckets, and that's not counting the vast number of small ports in isolated colonies that will need something from time to time. (They can probably poach from the larger forces on an as needed basis.) If we divide evenly that leaves about 45 escorts per location. Which looks adequate until you consider that this includes a lot of small and improvised ships (only about half of these will be destroyers), and a fair number of those will need to be laid up at any given time. (To clean hulls, maintain engineering plants, rest crews, reprovision, and so forth.)

So things are a bit thin.

Not impossibly thin, but thin. Thin enough to warrant a whole bunch of hasty building programs to fill the gap. Thin enough to make folks pull their hair out trying to make sure there are enough escorts in all places.

 

Indeed they did, and the Admiralty was actually ahead of the game on this one.
Actually my estimate was a bit low too, there were about 180 ASW trawlers operational by 1939, but they were short range, so would mostly be use for harbour defence & to patrol coastal waters.
In addition to the 210 or so destroyers available at the outbreak of war, the British had about 50 ASW sloops, the Shoreham, Kingfisher, Grimsby & Black Swan classes (and others) which would be used as escorts, along with some destroyers.

There were only three primary escorted convoy routes from 1939-1941, UK - Halifax (Atlantic), UK - Freetown (Africa) and Gibraltar - Alexandria (Med), although the last one basically ended by early 1941, except under full escort. There would be 20 - 25 escorts for each route, so in addition to the sloops, there would be a few dozen destroyers, (mostly the older V & W types) but the bulk of the destroyers would be used for fleet operations, not for escort.

The RN certainly made ASW a priority, in addition to the 175 Flower class ordered in 1939-1940, they also ordered 20 more Black Swans, 84 Hunt class Escort Destroyers, about 40 more ASW trawlers, and began the design of the River class frigates, seen as a replacement for the Black Swans, but cheaper and easier to build.
That's about 320 more ASW ships ready for use in 1941 or beginning of 1942, in addition to the 225 or so sloops & trawlers that they started the war with.

In contrast, the USN had very few ASW ships by Dec of '41, and the ones they did have were mostly fleet destroyers that were less capable as escorts than sloops, corvettes & frigates.
Even after war broke out, the USN was slow to order escorts, likely because Admiral King didn't make convoy escorts a priority.
In mid '42 the US ordered Submarine chasers, Buckley Class Destroyer Escorts & Tacoma class Frigates, but none of them would be operational until Mar/April 1943, which is why the US found it's ASW defences critically unprepared for about the first 16 months of the war

 

When the war started, yes, the Royal Navy took ASW quite seriously. And they initiated measures to cover their deficiencies, like ordering corvettes and buying fishing trawlers. From what I can find the RN started buying trawlers in large numbers in mid 1939. Conversion was quick and easy, so they were available almost immediately, but it's still clear this was a measure taken in extreme haste, and that fishing trawlers with a four inch gun and a couple of depth charge rails weren't the ideal escort.

I don't think US numbers were especially insufficient. The US had roughly the same number of destroyers (a hair less than 200) and fewer shipping routes and fleets to defend. And by January of 1942 it looks like the USN had several hundred sub chasers, ASW capable minesweepers, and USCG cutters (now rolled into the Navy department for wartime purposes.) (Different name, but much the same idea as sloops and trawlers. And probably better ships for the job than the latter.)

I'd say the bigger lack in the USN was doctrinal. King didn't initiate a convoy system along the US east coast until Paukenschlag and the "second happy time" demonstrated that the Royal Navy had been right about the U-boat threat all along. (Oh dear. So sorry old chap.)

What the Royal Navy had going for it was experience with the convoy system and ASW from the previous war, and a willingness to improvise.

But I'm a little curious about your contention that fleet destroyers are inferior escorts. I will grant that assigning them to escort duty is a bit wasteful, as they have significant surface capabilities that won't be terribly useful in ASW, but what do they lack? They have greater range than typical corvettes (particularly US destroyers designed for duty in the Pacific.) They have depth charge tracks and launchers of various types are fitted as soon as they are available. At this early stage no warship has the sorts of specialized pattern launchers that become so important in the late war, so the escorts have no significant advantage there. They have hydrophones and sonar. What am I missing?

If sloops, corvettes, frigates, and so forth are better ASW escorts, why were they never assigned to fleets and task forces? You wouldn't assign inferior escorts to your high value warships. (Even DDEs were used only for second line escort. The first line was always and invariably fleet DDs.)

So I'll grant that you don't want to be forced to assign fleet destroyers to convoy escort since you need them with the fleet, but I see no reason beyond that. The problem with destroyers isn't really that they're not perfectly capable escorts, it's that they're far too expensive too be economical. You're not going to build a thousand destroyers, but you might conceivably need a thousand escorts. They're just too much warship for the job.

Anyway, don't get me wrong, I will entirely grant that the RN was better prepared for ASW from the very beginning of the war. But it still seems they were spread rather thin. And they were spread thin in every type of warship, particularly aircraft carriers, of which they had more than anyone else, even though they were never able to muster enough in one place. (To be frank, this is largely a function of the wide geographic span of the empire, but you really can't ignore that. The Royal Navy was committed almost literally everywhere on earth.)

Further, one could say that the RN and USN were fighting different wars, and had prepared to do as much. The RN had been looking at Germany as the primary threat since before WWI. The US had looked to Japan in much the same way for about the same period of time. Is it any wonder that the RN was better prepared to fight the sorts of threats Germany could field? The US was, after all, quite a bit better prepared to fight Japan. (Which was still a near run thing early on.)

 

The only possible advantage I can come up with in specialized escorts over a fleet destroyer is the DD engine noise degrading ASDIC performance and possibly better accomodations for ships that were designed wth the need to keep the crews combat effective for lenghty convoy operations in mind. Another possible is depth charge capacity, as for escorts it was usually larger than for the average DD but fot the rest a 1939 fleet destroyer looks as good, if not as cost effective, ASW platform as a contemporary sloop.

An interesting statistic from Roskill
Merchant armament on March 1 1941
Surface guns
armed ships 3.434 including 491 non British

Anti aircraft
Lewis guns 1.400
Savage lewis guns 1.250
Hotchkiss guns 4.589
Hloman projectors 1.051
Parachute and cables 605 (AA device)
Kite eqiopment 2.289

200 Bofors 40mm were being delivered

Main inbound atlantic convoy routes
Halifax H.X.
Gibraltar H.G.
Jamaica K.J.

 

DC capacity would surely be an issue. I should think screw noise would be similar at similar speeds. Hull form will play into it some, but I don't think anyone was really designing with either hull noise or propeller cavitation in mind. (And submarines will have the advantage there anyway, since cavitation is a pressure function. The cavitation speed of a given system will be significantly higher at greater depths.)

I suppose that at the sorts of slow speeds that silent running requires beamier hulls with a tighter turning radius might well be a modest advantage.

Does anybody have a good source on cavitating speeds for different surface combatants during WWII?

 

I think it's in wiki.
If you go here: List of ship names of the Royal Navy - Wikipedia, the free encyclopedia
then select the type of interest say sloops
Then go to the list at say List of corvette and sloop classes of the Royal Navy - Wikipedia, the free encyclopedia
you'll get a list of classes
for instance: Black Swan class sloop - Wikipedia, the free encyclopedia
and you'll find thier speed to the right in this case 19 or 20 knots depending on whether it's a modified Black Swan or not.

 

Bravo Zulu regarding the data and statistics regarding the Alied ASW assets brought forth in this thread. Clearly ASW in the Atlantic significantly differed from that in the Pacific. Despite certain sophistication, Japan failed to maximize using their submarines. The US Submarine Force did to Japanese shipping what the Germans did to the RN. During most of the conflict, submarines and submarine warefare were pretty much lacking in sophistication. Submarines were nothing but ships that could submerge. In fact they did most of their attacks on the surface at targets made up of slow lumbering helpless cargo ships. I don't believe that cavitation was ever a concern around howling winds and rough Atlantic seas. Sonar was unreliable. Most engagements were generally visual in nature. Freebird was right. There was definitely pist poor planning and crappy leadership among the Allies. BTW, my first ship while in the US Navy in 1955 was the USS Essex (CVS-9), an ASW aircraft carrier. Although she had a pair of hydraulic catapults, most of our ASW aircraft were propeller driven and generally take off unassisted. In 1957 I transitioned into the submarine service and spent 11 years in various fast attack diesel submarines. Most ships cavitate and that's a good way of finding out their speed over the water. Cargo ships were notorious in that most of the time their screw stick out of the water. Of course there is no comparison regarding the technology surrounding submarines and submarine warefare nowadays.

 

^lwd

I was trying to find their "silent" speed, or how fast they could run without causing cavitation. (Which is quite noisy.) Ships and boats will make noise in the water for several reasons, most of which amount to turbulence of one kind or another. (And beamy hulls have a higher resistance and cause more turbulence, and thus will have more hull noise.) But cavitation is special. As a screw turns through the water it creates a areas of lower water pressure near it's surface. The faster the screw turns (and travels through the water) the greater the resulting reduction in pressure. If the pressure differential is enough to overcome the surface tension of the water "voids" of water vapor can develop. When these voids collapse they make quite a lot of noise. This is cavitation, and the speed at which a vessels props cause cavitation is well below the top speed of the vessel. (And it's also a function of depth, as the greater pressure of deeper water makes it more difficult to create these voids.) That's really what I was getting at, and it's different for every vessel, because screw design, at least, figures into it greatly. (A more efficient screw that propels the vessel more quickly with fewer rotations will be give you a higher "silent" speed than a less efficient one.)

And as I think about it the greater resistance of beamier hulls will require more power from the engines for the same speed, which will equate to more turns for a given prop and thus a lower speed at which cavitation will begin, ergo the fleet destroyers should be able to travel more quietly at a higher surface speed than the corvettes, sloops, and frigates. (This on top of the fact that the beamier hull will be noisier per knot anyway, since hull turbulence is audible.)

 

While I was on sub duty in the San Diego, CA area, the sub I was on will start to cavitate at 1/3 speed. While on silent running, we go dead slow or just hover dead stop. We were also equipped with "para-masker" but sonar technology has so improved that you can drop a pin aboard sub and ASW vessels can pick up the sound miles away. Also we seek depths at isothermo level whereby sonar may detect us but not in the position indicated on their sonar screen. Regarding cavitation, to reduce its effect I believe that nukes use seven or eight bladed low pitch propellers. Each blade has a small hole through it to minimize cavitation but has minimal effect on speed.

 

I know the Italian corvettes had secondary electric engines for very silent slow speed (5 knots max.) ASW work, possibly useful only in the quiet waters of the Med, so even engine noise was considered an issue. Non cavitatating speed for ASW ships is going to be a hard find, is the 1/3 max speed a reliable rule of thumb. The diesel/electric or Turbo/electric machinery of DE was probably less noisy tha a DD but the Captain are mid/late war ships

 

In that case my guess is the best bet is to try and find copies of the tactical manuals (or whatever they are called) for the classes of interest. It probably won't list the cavitation speed directly but it might tell the speed at which the sonar gave reliable results. Note that one of the advantages of cheaper ships is you can have more of them and use cooperative tactics such as one ship traveling at extremly slow speed and using sonar to direct other ships dropping the depth charges. Especially in a sloop I would think you wouldn't want to roll them off the back if you were moving too slow. Projectors would help some in this context.

 

^^TOS

My experience with steam and diesel powerplants is railroad experience, but I'm going to have to say that reciprocating steam powerplants, at least, are in my experience far quieter for the same power output than diesel plants. Diesel prime movers have many more moving parts and operate at much higher rpms than steam locomotives. Further, the exhaust of a diesel is much sharper, as it's essentially a controlled explosion. Steam turbines will be somewhat different, no doubt. You should get less vibrational noise, but the operating pressure is higher so the exhaust might be more of a concern. On the other hand, steam exhaust noise is mostly a function of turbulence. If the nozzle is broad enough and shaped efficiently enough to cause minimal back pressure and smooth efficient flow, even at high pressures it should be pretty quiet. (Comparably sized locomotives from the twenties tend to be louder, as the exhaust nozzles are often narrower and less efficient, even though locomotives from the thirties and forties usually operate at higher pressures and produce greater power.) Further, since maritime steam plants are closed loop, they'll probably be quieter anyway. (The steam is exhausted not into the atmosphere, but into a condenser, from whence it is returned to the feedwater supply.)

Actually, in some ways the best comparison might be a power plant. I walk down a street past the local University's steam power plant from time to time. On a summer evening they'll have the doors into the turbine room open. (Which is pretty cool, really.) The turbines, which are a closed loop design in most ways similar to a marine steam plant, make some noise, but they're still quieter than passing traffic. (And vastly more powerful.) To tell you the truth, I'd expect a diesel tug to be audible long before a steam destroyer. The Italian corvettes may well have had a battery system precisely because the diesel plant was so loud.

^lwd

All things being equal, yes, cheaper is better. I fully agree with you there. And very well said.

 

SymphonicPoet

The US were woefully short of ASW boats hence the reason the RN dispatched ASW Trawlers from the RNPS to assist the US off the US coast.

February 1942 24 trawlers were sent with mostly Royal Naval Patrol Service crews and made up the British 22nd A/S Strike Group, they were to be based in Boston, New York, North Carolina and Norfolk Virginia, 6 in each. This was less than was requested but all that was deemed safe to send.

The trawlers were HMT ARCTIC EXPLORER, BEDFORDSHIRE, BUTTERMERE, CAPE WARWICK, COVENTRY CITY, HERTFORDSHIRE, KINGSTON CEYLONITE, LADY ELSA, LADY ROSEMARY, LE TIGER, NORTHERN CHIEF, NORTHERN DAWN, NORTHERN DUKE, NORTHERN ISLES, NORTHERN PRINCESS, NORWICH CITY, PENTLAND FIRTH, SENATEUR DUHAMEL. SAINT CATHAN, SAINT LOMAN, SAINT ZENO, STELLA POLARIS, WASTWATER, WELLARD

There was also 10 Corvettes transferred and 53 Sqn RAF sent to assist with Maritime Patrol.

The Trawlers despite being completely unsuitable did do convoy escort across the Atlantic and to Russia at the start due to the lack of anything better. They even managed a few successes against U Boats. Later they were moved to the more suitable role of 'buttoning up' I believe it was called, taking over from and handing over to the ocean escorts closer to shore and doing the convoy formation.

 

I know one of the guys that was on the expidition that found U215 she rests in about 270 ft of water off the south west coast of Nova Scotia. She was a type VIID uboat designed to lay mines She was on her way to mine Boston Harbour when she torpedoed and sunk the liberty ship Alexander Macomb. The sub was then detected and sunk by the escort trawler HMS LE Tigre .