Improved interwar RAF/RN ASW

[Admiral Beez]

Is there anything Britain could have done between the wars to better prepare the RAF and RN to tackle the ASW needs of 1939-41?

The RN was working on the issue, Sonar - Wikipedia

"The British tested their ASDIC on HMS Antrim in 1920 and started production in 1922. The 6th Destroyer Flotilla had ASDIC-equipped vessels in 1923. An anti-submarine school HMS Osprey and a training flotilla of four vessels were established on Portland in 1924."

 

[SaparotRob]

I really don't see how. The U.S. could use blimps, Piper Cubs and civilian boats for submarine patrols from the safe skies of the U.S. Not an option for Britain as it was so close to enemy held shores. Britain was working on sonar, a new technology and like anything groundbreaking, that takes time and experimentation. There were some interesting developments by Barnes-Wallis. I vaguely remember that he developed a bomb launcher that fired rockets in a figure 8 pattern that became known to the Americans as "Hedgehog". This project had been put aside for a while, I think. Sir Barnes-Wallis had a number of balls in the air. It was very effective compared to dropping depth charges off the stern. Perhaps if it had been brought to light sooner, a more effective ASW program could've been in place sooner.

 

[ThomasP]

The only thing I and my friends in wargaming have come up with is if the RN & RAF had spent more time and resources on training, development and integration of their methods/systems. If they had done this it is possible that they would have realized the limitations of ASDIC sooner (ie before the war) and maybe have gotten their ASW units up and running sooner than they did historically (preventing the worst of the U-boat problem).

 

[Admiral Beez]

Was an interwar concept of the merchantman converted CVE too outlandish?

 

[MikeMeech]

Is there anything Britain could have done between the wars to better prepare the RAF and RN to tackle the ASW needs of 1939-41?

The RN was working on the issue, Sonar - Wikipedia

"The British tested their ASDIC on HMS Antrim in 1920 and started production in 1922. The 6th Destroyer Flotilla had ASDIC-equipped vessels in 1923. An anti-submarine school HMS Osprey and a training flotilla of four vessels were established on Portland in 1924."

Hi
I suppose there is always a way to do 'better' although overall the British were already more advanced on the subject of ASW than other countries including the USA. Indeed US 'imported' information on technique and technology for ASW directly from Britain and also via Canada. Even so the USN response to U-Boats off the East Coast in 1942 was 'poor' and British/Canadians even transferred ships as well as equipment and training techniques to the USN to help.
Books of interest on this include; 'Seek & Strike, Sonar, and anti-submarine warfare and the Royal Navy 1914-54' by Willem Hackmann, 'Hitler's U-Boat War, The Hunters 1939-42' by Clay Blair, and 'Depth Charge, Royal Naval Mines, Depth Charges & Underwater Weapons 1914-1945' by Chris Henry.
Britain was on its own for ASW development in the early years of the war and fairly 'rapid' progress was made as lessons were learned (and cash flow increased), I am not sure if a great deal more could have been done pre-war unless other 'urgent' priorities were moved down the list of things to be done, so what would be dropped to improve ASW development?

Mike

 

[SaparotRob]

Was an interwar concept of the merchantman converted CVE too outlandish?

Not to me. I don't think H.M.S. Argus or U.S.S. Langley were that much larger (if at all) then most merchantmen. Some of the aircraft in service in the mid thirties could use the shorter flight decks. The use of these ships in ASW training could have sped up development of ASW techniques. Need a faster hull. Need these areas of aircraft performance improved. Etc. The British were using blimps for search missions in WWI (?) so the concept was around.

 

[Admiral Beez]

Not to me. I don't think H.M.S. Argus or U.S.S. Langley were that much larger (if at all) then most merchantmen.

Whilst conversions, those were actual, proper fleet carriers though, just small ones. For example, here's HMS Argus sailing with the Royal Navy battlefleet, and USS Langley in port in support of the USN battlefleet.

I'm referring more to HMS Audacity or the USA's Long Island-class escort carrier, converted from merchantman, just with a flattop on top for a few ASW Swordfish. Audacity had no hangar, though Long Island did. For example, here's a cargo ship being converted.

 

[EwenS]

There are a couple of areas that deserve consideration before looking in detail about weapons and equipment.

What was lost in 1918?
The RN/RNAS had built up a very effective system for tacking U-boats in 1917/18. On 1 April 1918 when the RAF formed there were nearly 3,000 aircraft, 100 airships and 126 coastal stations most of which were dedicated to ASW. And there was the intelligence, command and control systems to back that up. Most of that was undone in the early years of peace only to have to be rebuilt from the mid1930s.

So if some more of this structure could have been retained inter-war Britain would have been better placed in 1939.

The nature of the ASW war expected.
In WW1 U-boats were based in Germany and Belgium (Zeebrugge for example). U-boat activity was largely concentrated in the North Sea and the eastern Atlantic, limited by the range of those U-boats. British planning inter-war was planned on the same basis.

The French surrender in June 1940 was a completely unplanned for game changer. All of a sudden U-boats were based on the Atlantic coast and able to range into the central and western Atlantic. The ships and aircraft then being introduced to service were rendered unsuitable overnight. The first U-boat "Happy Time" was July-Oct 1940.

Once Germany lost the French U-boat bases which were closed down in Aug 1944, the U-boat war moved back into U.K. inshore waters.

So the Flower class corvettes designed and ordered in 1939 (56 ordered before war broke out and another 60 on the first day of the war plus more for the RCN and which could be built in as little as 4-6 months) and which began to enter service from April 1940 were suitable for the ASW war planned but not that which transpired. The successor class was the River class frigates designed in late 1940 and laid down from early 1941 and completed from Spring 1942 was a reaction to that change.

It was the same with the RAF. The short ranged pre-war Anson, borderline adequate (?) for North Sea operations was being superseded by the Hudson from 1939, but even it did not have adequate range for Atlantic operations. 1941 saw but 10 Liberator GR.1 entering service. It was 1942 before more B-17 & B-24 began to arrive in service to help plug that Atlantic Gap and 1943 before enough really became available.

In an expected WW1 scenario shore based aircraft should have been adequate to protect shipping. Inter-war the RN did consider the need for "Trade Protection" carriers. But they were for hunting raiders. But with funds limited, fleet carriers came first. In that context the CVE was unnecessary. They only become necessary as the need to push air cover further out into the Atlantic begins to arise. Hence Activity being converted in the first half of 1941.

The CAM ships are also a reaction the arrival of the Fw200 Condors from French airfields after June 1940.

So, yes there are some things that could have been done to for example get the RAF to concentrate more on ASW and co-operate with the RN. But the thing that would have made the greatest difference is for someone's crystal ball to predict the ASW war that actually came about.

 

[Shortround6]

What was lost in 1918?
The RN/RNAS had built up a very effective system for tacking U-boats in 1917/18. On 1 April 1918 when the RAF formed there were nearly 3,000 aircraft, 100 airships and 126 coastal stations most of which were dedicated to ASW. And there was the intelligence, command and control systems to back that up. Most of that was undone in the early years of peace only to have to be rebuilt from the mid1930s.

So if some more of this structure could have been retained inter-war Britain would have been better placed in 1939.

The nature of the ASW war expected.

There was a lot that had been lost and it took a lot of time to regain it. Often in bitter opposition by elements in the RAF that believe that the RAFs job was to bomb German centers of production and everything else was a distraction at best.

It was the same with the RAF. The short ranged pre-war Anson, borderline adequate (?) for North Sea operations was being superseded by the Hudson from 1939, but even it did not have adequate range for Atlantic operations. 1941 saw but 10 Liberator GR.1 entering service. It was 1942 before more B-17 & B-24 began to arrive in service to help plug that Atlantic Gap and 1943 before enough really became available.

Anson was far from borderline adequate. It was better than using a Puss Moth

but once you have said that you have covered the Anson pretty well.

It was 1942 before more B-17 & B-24 began to arrive in service to help plug that Atlantic Gap and 1943 before enough really became available.

The gap moved a lot. It was pretty bad in the summer of 1941 however it wasn't that bad in 1940. So the British had about 1 1/2 to two years to get it somewhat under control. Or at least move the Germans further away form the costal areas and into the Atlantic.

In 1939 the British had more submarines than the Germans did.

We do have a number of threads on this subject.

What was known to the British at the end of WW I was that flying around 'boring holes in the sky' didn't work and without a major change in technology it wasn't going to work in the early part of the WW II. The British had flown spider web patrols for over a year during WW I.

there were other areas where this search pattern was flown in. The British made a number of attacks during this patrols and claimed 5 subs hit or sunk which was a poor return for the amount of time spent on these patrols. It also turned out that the German records showed only one U-boat sunk out of the 5 claimed so it really wasn't working.

Flying fixed patrols hoping to run across a surfaced sub (or one showing a periscope in calm seas) was pretty useless. The subs could spot the aircraft much further away than the airplane could spot the submarine.

And if the sub was 30-100 miles away from a convoy, who cared? Only people who were keeping a scoreboard mentality.

What counted was the number of ships that made it through while being convoyed or for more scientific numbers the number of ship voyages or even ship miles sailed per sinking.

During WW I in the last 18 months of the war there 84,000 voyages in convoy. The Germans sank 257 (damaged not give) of those convoyed ships when accompanied by ships alone. Off those 257 ships only 2 were were sunk when the convoy enjoyed both the protection of ships and aircraft.
One the flip side of the near useless patrols 4 U-boats were sunk at or near convoys by aircraft and escort ships working together.

All of this was thrown away between the wars and much of it had to be relearned.

As far as anti-sub weapons go the most common aircraft anti-sub weapon of WW 1 was the 116lb bomb (most of the aircraft were lucky to carry two of them, some could only carry one, a few could carry four and a very few planes could carry a larger load.
The British spend about 8 years (?) designing the 100lb AS bomb, build a handful (?) never exploded one (?) using HE and yet proclaim it great, lock the drawings in a cabinet for over 10 years and don't even order it into production until 1938 (?) which means first issue wasn't until 1939.

Our mighty sub hunting Anson carried two. Twenty years after WW I ended the most numerous Costal Command aircraft carried a lighter bomb load than many WW I biplanes.

Harris was actually quite right when he did not want to send valuable bombers out to swan about over the ocean looking for submarines. However the answer was also not to try and bomb the building docks but to fly aircraft (with a decent bombload) over/near the convoy and let the subs come to the convoy to be bombed by the aircraft and depth charged by the alerted ships.

The first year or two of the U-boat war could have gone a lot different without any huge changes. The Germans didn't have that many long range boats although they were working on more. In Sept of 1939 they only around 20 boats with a range of over 8-9,000 miles. Until the Germans get driven out of the costal areas the mid Atlantic hunting zone is not a a large concern.

 

[Glider]

Was an interwar concept of the merchantman converted CVE too outlandish?

There was a plan to convert a couple of liners into carriers, the ships had been identified and the design work completed. However, when the war started the liners fell into the department responsible for merchant shipping and they wouldn't release them from trooping duties.
For some unknown reason no one knocked heads together and there was a delay of a couple of years before the project restarted

 

[Admiral Beez]

For some unknown reason no one knocked heads together and there was a delay of a couple of years before the project restarted

It wasn't until the Americans got into the game that anyone thought about series production of CVEs. I wonder if there were bureaucrats or traditionalists in the RN that blocked the idea between the wars.

 

[Shortround6]

It wasn't until the Americans got into the game that anyone thought about series production of CVEs. I wonder if there were bureaucratic blockers in the RN that blocked the idea between the wars.

There could have been a bunch of blockers and there might have been none.

Or simple budget problems, like who pays for them and what don't you get without providing more money.

Naval ships had different rules of design compared to merchant ships which included hull plate thickness and deck thickness and the the dimensions of the angle plates that held sides, decks and bulkheads together. And a bunch of other details, If you want to use cheap merchant construction you have to OK it and plan for it.
By the way, the Flower class corvettes were built to merchant standards. Certain classes of small ships may have been built to merchant standards in the First WW I.

And until Britain gave up on the treaties you were limited to total tonnage of aircraft carrier hulls, no freebees if you built a bunch of small, slow ships.

Finding suitable merchant ships to turn into substitute warships was actually not that easy. The Axillary cruiser program went back well before WW I. Sometimes companies were given a subsidy by the government to pay for certain features that weren't really needed for commercial use or that help pay operational costs. If war didn't breakout for a number of years the company came out ahead, If war came soon the RN came calling for the ship and the shipping company didn't get it back until the war was over or the Navy didn't want it anymore (assuming it was still afloat).
Please note that the Army had similar schemes for draft horses going back into the 1800s and had come up with a scheme for trucks in the 1920s and 30s.
Problems wound up similar to ships, if the war took a while your civilian transport network (and your war production transport network) was operating at reduced capacity until or if the subsidized horses/trucks were returned.

 

[Shortround6]

This is from wiki as I am being a bit lazy, correction welcome.

"On the outbreak of war in 1939 Coastal Command had forces of ten Avro Anson, including four auxiliaries, two Vickers Vildebeest, two Short Sunderland, three Saro London and one Supermarine Stranraer squadrons. The Vildebeest and London were all obsolescent. The Ansons made up half of this force, but with insufficient range to undertake deep ocean reconnaissance it was left to the flying-boat squadrons, of which four out of six had obsolescent machines. This left three squadrons with suitable aircraft, the Lockheed Hudson and Sunderland that could operate effectively."

Not all squadrons were up to strength or what we would consider up to strength 80 years later. Consider the 3 Saro London squadrons. They only built 31 planes total from 1934 to 1938, were all still in service?

Things did NOT get better quickly.
"In December 1939 to August 1940 the following reinforcements were sent: No. 10 Squadron RAAF received Sunderlands, No. 235 Squadron RAF, No. 236 Squadron RAF, No. 248 Squadron RAF and No. 254 Squadron RAF equipped with Bristol Blenheims from RAF Fighter Command in February 1940; in June 1940 No. 53 Squadron RAF and No. 59 Squadron RAFs with Blenheim on loan from RAF Bomber Command, and in August 1940, No. 98 Squadron RAF's Fairey Battles, also on loan from the Bomber Service and based in Iceland. "

So in just about year they had added about 1 flying boat squadron, two squadrons Blenheim bombers and 4 squadrons of fighter and one squadron of Battles.
Think about that one, Flying over water patrols four hours (even if they stayed close to shore) in a single engine aircraft over cold, even in summer, water.

I have suggested before re-equipping 4-5 of the Anson squadrons with Blenheim IVs in summer/fall of 1939. Not a big change in manpower and not a big change in Bomber command striking power. One Wellington can carry 3-4 times the bomb load of a Blenheim so reduction in actual bomb dropping capability is not that great for BC.
However, if you can equip the Blenheim's with 250lb anti-sub bombs the Blenheim's have 5 times the bomb load of an Anson (Not quite because it is 4 bombs not 5 and you do have to hit). However the Blenheim has got twice the range/endurance of the Anson and can patrol (orbit convoy) for two hours about 400 miles from base with 1 hour reserve fuel.
Keeping the crew warm might be problem but can't be any worse than that Flying boat.

The Anson can't even fly to 400 miles from base and make it home. It might make it to 160 miles, patrol for 2 hours and make it home on fumes.
A Blenheim at 160 miles from home can stay on station for 4-5 hours.
A Blenheim can fly from Scotland to the Norwegian coast as stay for a few hours, the Anson cannot.

You can get a lot more done with the same number of planes and aircrew.

If you have the time and money to build escort carriers in 1938-39 look into buying 6-8 PBY Catalinas in 1939. Replace one of the biplane flying boat squadrons with Catalinas. Send some the extras to Gibraltar to keep that squadron up to strength.( at least the crews will be warmer?)

All the basics of using longer endurance aircraft vs short endurance aircraft had been worked out in 1917-18. No retrospectroscope needed.

Use about Squadrons of Ansons for close patrol/ convoy escort near British shores.

Give the extra Ansons to training command.

 

[Tkdog]

I might be influenced by having served in Iceland, but something that could have been done was building an air base there. Having that on day one would be a significant benefit.

The day will come we regret closing NAS Keflavik. Bush 2 closed it down.

 

[ThomasP]

Iceland was independent at the time.

From Wiki:

"Iceland officially remained neutral throughout World War II. However, the British invaded Iceland on 10 May 1940. On 7 July 1941, the defence of Iceland was transferred from Britain to the United States, which was still a neutral country until five months later."

 

[EwenS]

I might be influenced by having served in Iceland, but something that could have been done was building an air base there. Having that on day one would be a significant benefit.

The day will come we regret closing NAS Keflavik. Bush 2 closed it down.

While the Keflavik base may have been closed, access to its facilities did not end. And in 2017 US funding was obtained to upgrade its facilities to accommodate the P-8 Poseidon. Work on new hangars, aprons etc began in 2020 and is scheduled to complete next year.

Having occupied Iceland in May 1940, Britain found that the existing airfield at Reykjavik was entirely inadequate without reconstruction. It was a grass strip prone to flooding. As an interim measure a new site at Kaldarnes was identified as a suitable airfield site (one of the few on the island). Work began immediately and was sufficienly far advanced that 98 squadron with Battles was able to move in during Aug 1940. It didn't officially open as an RAF base until early June 1941, and it took until July 1941 for all three runways to be completed. Hudsons of 269 squadron moved in during June 1941. But it was never an entirely satisfactory site and prone to waterlogging and even flooding which proved particularly bad in spring 1943, leading to its closure later that year, other than for some limited FAA use. Some of the buildings were dismantled and moved to Keflavik in 1943.

Reconstruction of Reykjavik began in Oct 1940 initially using the labour of the British Icelandic Garrison and the conditions proved difficult. It opened as an RAF base in March 1941.

Prior to, and after, that various flying boat squadrons had used Reykjavik harbour as a base to be supplemented and later replaced by USN squadrons.

The US agreed to take over the garrisoning of the island as part of an agreement to free up British troops for use in other theatres. That process lasted into 1942.

 

[yulzari]

We do forget that the French were to (and did prior to the BoF) play a part in the ASW plan and action. Operating from west coast bases. Both in the air and at sea. This would have grown and mutually developed had the Germans been stopped in 1940. The fall of France stretched the Royal Navy into work they never expected to need to cover and air cover would not have had to reach into places like the Bay of Biscay etc. so could concentrate on the western approaches to the UK.

It would have been a nice 'what if' had there been an air base in south western Ireland to extend the effective range of the OTL maritime air cover. Perhaps it could be sweetened by it being an Irish site and Irish run and just having the British pay to use it and only having the operational squadron staff in place. ie the main engineering and support being Irish. Maybe even having it a French site instead to cover the western approaches to France? However that is a whole other thread and this one is no place to go into the idea.

 

[EwenS]

You will find maps of the monthly allied shipping losses to U-boats here.

Ship losses by month - uboat.net

The U-boat War in World War Two (Kriegsmarine, 1939-1945) and World War One (Kaiserliche Marine, 1914-1918) and the Allied efforts to counter the threat. This section includes over 21.000 Allied Warships and over 11.000 Allied Commanders of WWII, from the US Navy, Royal Navy, Royal Canadian...

uboat.net

Note how from Aug 1940 they begin to stretch further into the Atlantic and northwards as a result of U-boats being based in France.

Also note that convoys heading for Britain were largely unescorted in the early part of the war until they reached the Mid Ocean Meeting Point. Similarly convoys leaving Britain were escorted only to that point. Through escorting only became necessary from mid-1941, at which point the numbers and types of escorts required changed. U-boats we're constantly moving westwards in the Atlantic, trying to get to convoys before the escort arrived. Again look at the pattern of sinkings over time.

Mid-Ocean Meeting Point - Wikipedia

en.m.wikipedia.org

 

[Geoffrey Sinclair]

By definition more could always be done and we now know the best answers. There was a major loss of memory from the armed forces post WWI, the RAF was reduced to 29 squadrons in March 1920, the British shipbuilding industry collapsed in the 1920's.

In terms of tactics asking the RN submariners to come up with ways of attacking assuming ASDIC equipped defenders would have helped form ideas about submarines making night surface attacks. Thinking on how to handle one on one encounters would have pushed ideas about ahead throwing weapons. Considering the unthinkable like multiple submarines versus escorts. Add the way the submarines were becoming stronger and longer ranged requiring adjustments in weapons and anti submarine assets.

The move of 4 group and its Whitleys to Coastal Command pre war with the Whitley V that appeared end 1939 looking more like the GR VII version, to be superceded or supplemented in 1940 by a GR Wellington version. The planning of and dedication to at least 1 production line of the Stirling, Halifax or Lancaster to a GR version available in 1941.

For ships and aircraft the biggest increase in escort effectiveness was radar, followed by radio direction finding, in terms of cutting down the chances for submarines to attack and set up attacks on the submarine. If you like code breaking was strategic, direction finding and radar tactical. Then came weapons, including air dropped depth charges and attack tactics to sink the submarines and finally escort numbers, so a submarine could be outnumbered and hunted to destruction.

Until 1935 the RN anti submarine investigations were more theory than practice given the lack of hostile submarines generally and the Atlantic specifically. The big lesson from WWI was implemented, convoys. Anti submarine capacity, being mostly small ships, were to be built when war began or was highly probable. After the WWII experience the USN in the 1950's built some austere escort ships as a form of mobilisation prototypes but they had real problems in being value for money in peace time. Similar for the air escorts.

The first few months of the war were a struggle for both sides, Germany started the war with 57 U-boats of which 12 were considered to be trainers. To the end of May 1940 24 were lost versus 18 new ones built, at the start of May 1940 the fleet was at its wartime lowest point, 49, including 3 boats on trials and 15 for training. Giving the conclusion the mostly British anti submarine forces were effective in a scenario in line with pre war expectations, the U-boats were being pushed further away from Britain and taking steady losses, both sides were building up production.

In terms of merchant ships to end May 1940 Lloyds says around 800,000 GRT had been lost to U-boats versus around 530,000 GRT to mines, of these around 490,000 GRT lost to U-boats and 314,000 lost to mines were from the countries at war with Germany. There were plenty of neutrals at the time. So the exchange rate was around 33,300 GRT sunk per U-boat lost, and about 90,000 GRT sunk per month.

We also know how much the U-boat war was expanded and how much more the load on the British became.

The French Armistice gave the Germans much better bases and removed 140 French destroyers and escorts from allied anti submarine strength, plus patrol aircraft. While the British gained the best part of 10,000,000 tons of Belgian, Danish, Dutch, Greek and Norwegian shipping to escort in 1940/41.

Roughly the 13 months from June 1940 to June 1941 became a very successful U-boat period, with the first happy time being considered the summer of 1940. Around 3,156,000 GRT sunk, against 22 U-boats lost, or around 143,500 GRT per U-boat lost and around 243,000 GRT sunk per month.

The problem in March 1943 was the U-boats seemed to be able to finally break convoys, there were so many U-boats in service they could overwhelm the escort, Germany had just under 200 U-boats serving in the Atlantic

In September 1939 the RN had 107 modern and 79 older destroyers, plus 32 anti submarine ships, "escorts". By the end of 1940 the figures were 90 modern, 71 older destroyers, 50 ex USN destroyers, 19 Hunt class, and 88 escorts.

When it comes to costs, the following is a total cost of ownership, expressed as a yearly figure, that is to build, maintain, operate and upgrade. Australian Archives file A5954 1024/10, scan 38, costs probably in British pounds, of warships per year including major refits and rebuilds, lifetime of a battleship 26 years, lifetime of a carrier 20 years, lifetime of an aircraft 5 years. Nelson class battleship, 310,000 running costs, 34,500 aircraft, 307,000 replacement (build cost divided by lifetime), large repairs 54,800, (per year divided by lifetime) total 706,800 pounds per year. Carrier with 36 aircraft, 255,000 running costs, 414,000 aircraft, 202,500 replacement (build cost divided by lifetime), large repairs (per year divided by lifetime) 22,500 total 894,000 pounds per year. Carrier with 15 aircraft, 160,000 running costs, 172,500 aircraft, 162,500 replacement (build cost divided by lifetime), large repairs (per year divided by lifetime) 19,500 total 514,000 pounds per year.

Cruiser lifetime 23.5 years, destroyer 22 years, submarine 14 years. Annual costs large cruiser 323,600 pounds, small cruiser 225,400 pounds, J class destroyer 66,000 pounds, 1,000 ton submarine 65,500 pounds.

Given the RN had 7 carriers and 9 battleships under construction at the start of the war, Hermes and Argus were obvious candidates for training and/or ASW. The 1939 hunter killer combination of carrier and destroyers was tried, the counter attack missed Ark Royal but hit Courageous. In 1935 the RN trade protection carrier would be 10 to 20,000 tons, diesel powered, highest possible speed, at least a 70 foot wide flight deck, storage for 12 to 18 aircraft. Trouble is ships suitable for such conversions tended to be very valuable in their original state. It only took from 5 December 1940 to 2 January 1941 for the proposal to do a conversion and the Hannover to be allocated to become HMS Audacity. On 20 January the USN was requested to help provide 6 more Audacity type conversions from the US.

The US was thinking along the same lines at the same time but in 1940 was caught in the debate about how elaborate the design could be, early January 1941 ships were allocated, USS Long Island appeared in June 1941 after given a priority the same as USS Hornet, but with a short flight deck, it was extended in September.

When it came to the treaties there were originally exemptions for carriers under 10,000 tons, hence Ryujo.

Meantime the success rates of surface attacks on submarines goes something like this 1943 to 1945, depth charges around 4% with the possibility the table has a data error, but in 1945 it was 7%, hedgehog was managing 8% in 1943, 35% in the second half of 1944 and 26% in 1945, double squid was doing around 41% from mid 1944 onwards in 27 attacks, single squid, which did 23 attacks had a 26% success rate. From Naval Weapons of World War II by John Campbell

Coastal Command 3 September 1939
9 Squadrons of Ansons, establishment 200, serviceable 135.
1 Squadron of Hudsons, establishment 9, serviceable 9
2 Squadrons of Londons, establishment 16, serviceable 9
1 Squadron of Stranraers, establishment 8, serviceable 6
2 Squadrons of Sunderlands, establishment 16, serviceable 12
1 Squadron of Vildebeeste, establishment 16, serviceable 12

10 September 1939, operational strength, Fighter Command 373, Bomber Command 414 (including the 141 AASF Battles) Coastal Command 171

Note the above definition of establishment is I.E.+I.R. below it is I.E.

Coastal Command 31 August 1940
6 Squadrons of Ansons, establishment 126, serviceable 60 plus 7 with no crews.
4 Squadrons of Blenheim fighters, establishment 80, serviceable 47
2 Squadrons of Blenheim GR, establishment 36, serviceable 23 plus 4 with no crews.
5 Squadrons of Hudsons, establishment 105, serviceable 37
1 Squadron of Lerwicks, establishment 6, serviceable 0
1 Squadron of Stranraers, establishment 6, serviceable 2
4 Squadrons of Sunderlands, establishment 24, serviceable 17
1 Squadron of Beauforts, establishment 21, serviceable 2
2 Squadrons of Battles, establishment 32, serviceable 14, on loan from Bomber Command

Also present 3 Fokkers, 3 Wellingtons, 6 Bothas, 8 Swordfish, 3 Walrus, 5 Albacore and the PRU Unit aircraft.

Coastal Command was diluted in mid 1940 as places like the Mediterranean required patrol aircraft.

After producing PBY-1, -2, -3 and -4 more or less continuously September 1936 to June 1939 Consolidated San Diego was switching to the B-24 and PB2Y in 1940, PBY-5 production began in September 1940. The PBY-4 had 2,100 HP for take off, the PBY-5 2,400, the 1,750 gallons of unprotected fuel in the PBY-4 gave a greater range than the 1,460 gallons of protected fuel in the PBY-5, helped by an empty weight of 14,999 pounds versus 18,270. In mid 1939 the RAF was building the Sunderland for the long range ocean patrol role, the current gap was between it and the Anson.

In 1942 axis submarines sank around 6,080,000 GRT, or nearly 1,500,000 more GRT than had been sunk to the end of 1941. Much of this was off the coast of North America and the Caribbean. Improving submarine defences there would have a big impact.

 

[EwenS]

We do forget that the French were to (and did prior to the BoF) play a part in the ASW plan and action. Operating from west coast bases. Both in the air and at sea. This would have grown and mutually developed had the Germans been stopped in 1940. The fall of France stretched the Royal Navy into work they never expected to need to cover and air cover would not have had to reach into places like the Bay of Biscay etc. so could concentrate on the western approaches to the UK.

It would have been a nice 'what if' had there been an air base in south western Ireland to extend the effective range of the OTL maritime air cover. Perhaps it could be sweetened by it being an Irish site and Irish run and just having the British pay to use it and only having the operational squadron staff in place. ie the main engineering and support being Irish. Maybe even having it a French site instead to cover the western approaches to France? However that is a whole other thread and this one is no place to go into the idea.

In Jan 1941 Eire entered into a secret agreement with Britain to allow RAF aircraft to fly through an agreed air corridor to access the Atlantic via Donegal Bay. There were restrictions to fulfill the needs of Irish neutrality but in practice these were largely ignored by both parties. That became known as The Donegal Corridor and was the shortest route from Northern Ireland to the Atlantic. At the same time an RAF flying boat base was being established at Castle Archdale on Lough Erne. That was the most westerly point in Northern Ireland and Britain. That agreement extended the air coverage in the Atlantic by about 100 miles.

Eire also helped navigation from 1942 by painting the word "Eire" on 90 prominent capes and headlands around the country along with the number of the nearest Look Out Post in giant letters. There was a list of these numbers and locations distributed to RAF and USAAF aircrew who might need it.

The accidental bombing of Eire by the Luftwaffe from Aug 1940 didn't endear Germany to the Irish population many of whom supported Britain and in fact volunteered to fight in the British forces. It is surely no coincidence that there were 3 bombings in late Dec 1940 / early 1941 immediately prior to the secret agreement above.

Bombing of Dublin in World War II - Wikipedia

en.m.wikipedia.org

However, I think allowing construction of airfields on Irish territory for the use of the RAF would have been a step too far.