VLR B-24 Liberators and the Mid-Atlantic Gap

[Reluctant Poster]

But they did not stop more than 10% of the supplies, even though the ships they sank were capable of more than one trip. Read Hitler's U-Boat War by Clay Blair; he explains this. We did react to the U-boat success, built ships faster than they could sink them, and in 1944 were sinking something like 10 times the tonnage in U-boats that they were sinking in our ships. The Germans lost 500 U-boats in WWII, 10 times as many as the USN.

The idea that America won the war simply by building ships faster than the enemy could sink them is an argument with several large holes in it;
1. In addition to losing ships you are losing cargo which must be replaced. In some instances the cargo is virtually irreplaceable. For example the planned expansion of the enormous refinery at Abadan was delayed on two separate occasions, each time by several months due to a U-boat sinking the ship carrying the equipment.
2. There was a world wide shortage of shipping throughout the entire was. If all you're new builds are going into the lifeline to Britain the other theaters are going without. The Bengal famine which claimed 2 to 3 million lives was blamed in part on the prioritization of shipping for war materials.
3. There was a shortage of tankers. Tankers are much harder to build than cargo ships. The Germans knew this and made them priority targets. Admiral King stupidly lost 50 priceless tankers in the first 6 months of the war which was 10% of the allied fleet. After that tankers were always in short supply. Without oil the whole show grinds to a halt.
4. When the Royal Navy defeated the U Boats in May 1943 the USN was able to cancel a large portion of their destroyer escort program. This freed shipyard capacity to build landing craft. The was a shortage of landing craft through the war. without the additional landing craft operations would have had to be postponed. I would guess that the advance thru the Pacific would have suffered.
5. People. War is actually fought by humans. Any organization consistently losing 10% of its strength falls to pieces pretty quickly. Everyone is a rookie. Efficiency plummets. Serving in the Merchant Marine was one of the most dangerous jobs in the war. I think only bomber crews and, ironically, U-boat crews had a higher mortality rate. Approximately 30,000 mariners died terrible deaths, blown to bits when you're ammunition cargo goes up, trapped below deck when your ore carrier sinks within a minute of being torpedoed, burned to death when your gasoline tanker catches fire, scalded by steam in the boiler room or simply freezing to death in the Atlantic watching the other ships sailing off because they can't stop for fear of suffering the same fate. I'm amazed that morale didn't crack as it was, but if the loss rate had continued I doubt you would find anyone willing to go on a suicide mission.

 

[Shortround6]

Unless I am adding things up wrong the U-boats were sinking ships faster than they could be built in 1940 and 1941. The shipbuilders beat the U boats by about 17% in 1942 and it is probably true that it was in the last few months? Things may have been a bit on the iffy side at the end of 1942. Things looking better for the allies but not out of the woods yet, If Germans can get back to earlier success rates (or even close) then the surplus goes away.

The Allied introduction of new sensors and weapons means they keep the tactical initiative and the increase number of escorts just push that further.

The Germans failed to keep up the technical pace fell and behind quickly. A few extra AA guns or 20 tons more fuel oil is not really changing things by very much. They sat on the schnorkel for several years. They failed to enlarge the internal size of the boats for far too long and used those ridiculous deck storage tubes for reloads, which were pretty much useless in the North Atlantic, especially in winter. They kept a rather slow submerged speed, Under 8kts for the Type VII while the British T and U/V could make 9 and the S class could do 10kts. In a given amount of time (say 15 minutes) a boat that can do 10 kts has over 50% more "area" to disappear into than an 8 kt boat.

Please note I am not talking about new hull forms or type XXI subs.

The outcome of the Battle of the Atlantic was a lot harder to call in 1941 and most of 1942. Nov 1942 being a high point for the U-boats with 126 ships (802,160 tons) sunk. the next month saw the sinkings drop to about 1/2.

There is a difference between what we know now and what they knew then. Just a few really bad months in row would have meant real trouble but the Germans were not able to put 3 or more (or even two?) high scoring months together.

 

[DO335]

Why didn't the British bomb the U boat pens while they were being built on West Coast of France? If they had bombed around the time the cement was poured it would have destroyed them.

 

[syscom3]

Why didn't the British bomb the U boat pens while they were being built on West Coast of France? If they had bombed around the time the cement was poured it would have destroyed them.

Not enough bombers. And not enough time

 

[pinehilljoe]

Not enough bombers. And not enough time

The Pens are also as indestructible as a structure made by Man can be with 1940s bombing technology. They are still there in Lorient, too expensive to break up.

 

[SaparotRob]

The idea that America won the war simply by building ships faster than the enemy could sink them is an argument with several large holes in it;
1. In addition to losing ships you are losing cargo which must be replaced. In some instances the cargo is virtually irreplaceable. For example the planned expansion of the enormous refinery at Abadan was delayed on two separate occasions, each time by several months due to a U-boat sinking the ship carrying the equipment.
2. There was a world wide shortage of shipping throughout the entire was. If all you're new builds are going into the lifeline to Britain the other theaters are going without. The Bengal famine which claimed 2 to 3 million lives was blamed in part on the prioritization of shipping for war materials.
3. There was a shortage of tankers. Tankers are much harder to build than cargo ships. The Germans knew this and made them priority targets. Admiral King stupidly lost 50 priceless tankers in the first 6 months of the war which was 10% of the allied fleet. After that tankers were always in short supply. Without oil the whole show grinds to a halt.
4. When the Royal Navy defeated the U Boats in May 1943 the USN was able to cancel a large portion of their destroyer escort program. This freed shipyard capacity to build landing craft. The was a shortage of landing craft through the war. without the additional landing craft operations would have had to be postponed. I would guess that the advance thru the Pacific would have suffered.
5. People. War is actually fought by humans. Any organization consistently losing 10% of its strength falls to pieces pretty quickly. Everyone is a rookie. Efficiency plummets. Serving in the Merchant Marine was one of the most dangerous jobs in the war. I think only bomber crews and, ironically, U-boat crews had a higher mortality rate. Approximately 30,000 mariners died terrible deaths, blown to bits when you're ammunition cargo goes up, trapped below deck when your ore carrier sinks within a minute of being torpedoed, burned to death when your gasoline tanker catches fire, scalded by steam in the boiler room or simply freezing to death in the Atlantic watching the other ships sailing off because they can't stop for fear of suffering the same fate. I'm amazed that morale didn't crack as it was, but if the loss rate had continued I doubt you would find anyone willing to go on a suicide mission.

 

[SaparotRob]

Why didn't the British bomb the U boat pens while they were being built on West Coast of France? If they had bombed around the time the cement was poured it would have destroyed them.

I believe the "turncoat" Frenchman who was in charge of the facility was assassinated by the Resistance. It turned out he was working for British intelligence.

 

[DO335]

The Pens are also as indestructible as a structure made by Man can be with 1940s bombing technology. They are still there in Lorient, too expensive to break up.

I've visited one in France, I agree they appear indestructible.

 

[Elan Vital]

Why didn't the British bomb the U boat pens while they were being built on West Coast of France? If they had bombed around the time the cement was poured it would have destroyed them.

They did, but with such a small payload and so little subsequent bombing during construction that they didn't prevent their completion and after that there simply never was the consistent and focused effort to take them out/disrupt operations for good. The surrounding cities and civilian population took a heavy beating instead.

 

[pinehilljoe]

Base de Sous-Marins · 56100 Lorient, France

âââââ · Museum

www.google.com

Interesting to look at the street view on google maps. Next best thing to being there.

 

[EwenS]

These bunkers were built in incredibly short periods of time when you consider the volumes of concrete that were poured. Work at these sites went on day and night, under floodlights when necessary, only stopping for air raids. Even after they were completed, additional works were carried out to make them even more bomb proof by adding more concrete to some of the roofs, spaced from the first layer, along with concrete bomb traps to explode bombs before they hit the roof proper. Not all these works had been completed by the time that the U-boats were withdrawn from France in Aug 1944. And all these sites were well protected with flak guns and balloons.

Lorient
First air raid on 27 Sept 1940 showed the vulnerability of U-boats in the open harbour and triggered the design of the concrete pens.

2x "Dom" bunkers built to protect existing slipways in the shipyard
Scorff bunker (2 wet docks with 4 berths) completed Aug 1941.
Then:-
Keroman I (5 boats + protected slipway) work started Feb 1941 completed Sept 1941
Keroman II (7 boats + garage to protect the transporters) work started May 1941
The Keroman complex was designed to lift U-boats completely out of the water and repair them ashore. The first U-boat was brought ashore at the Keroman complex in Aug 1941 and the whole complex, with its transporter system to move U-boats around, was officially handed over to the KM on 20 Dec 1941.

Keroman III with 7 pens (4 designed with pumping equipment as dry docks) to hold 12 U-boats, saw work start in Oct 1941, with parts being used from early 1943 before it was completed in May or July 1943.

In Jan/Feb 1943 the Allies bombed Lorient town in an effort to cut off the supply routes to the U-boat bunkers. In doing so they flattened 90% of the town

Late summer 1943 work began on Keroman IVa & IVb, but never progressed beyond some foundation work.

Brest
Construction started Jan 1941 and the first pen was ready for use in Sept. 15 pens (10 dry dock & 5 wet)

Saint-Nazaire
Built from Feb 1941, with the first pens available for use in June that year. It was fully completed in Oct 1942. 8 dry and 6 wet docks. Following Operation Chariot a new protected lock to the basin in which the U-boat pen sat, was designed and built 1943/44, but it doesn't ever seem to have been used in WW2.

La Pallice / La Rochelle
Work started April 1941. The first phase (2 dry and 5 wet docks for a total of 9 U-boats) was completed in Nov. In April 1942 work began on a second phase of 3 pens (2 dry & 1 wet for another 4 U-boats). A protected lock was also built from July 1942.

Bordeaux
Construction began Sept 1941 and it became operational in Jan 1943. 11 pens (4 wet & 7 dry docks)

All these bunkers were targets during the construction phase but that was at a time when Bomber Command wasn't very strong, so damage was limited. By the time they became a priority after the beginning of 1943 at a time when Bomber Command was much stronger and the 8th AF was beginning to become available, most were complete. Instead the towns and cities around them were laid waste with significant French civilian casualties.

On 5 Aug 1944, 617 squadron dropped 14 12,000lb Tallboys on the Brest bunker. 6 hit the roof. Two penetrated the 18ft of concrete. Two others left craters 8ft deep. Brest was revisted on the 12th Aug. 3 hits were obtained completely penetrating the roof. Another raid on the 13th may have added another penetrating hit as well as causing other damage.

On 6 Aug it was the turn of Lorient. 3 Tallboys hit the roof of Keroman III but failed to make a complete penetration, although one hit did cause some crumbling, to thethickest part of the roof.

On 9 Aug 617 visited La Pallice. Again a number of hits were obtained causing craters or, in one case penetrating the top layer of concrete roof. Another visit was made on the 18th August. several non penetrating hits were obtained.

By 22nd Aug it was becoming clear that these structures were sufficiently stoutly constructed that neither direct Tallboy hits nor near misses to undermine the foundations would have the desired effect of destroying these targets. Tallboy did however prove effective against the more lightly built E-boat pens at places like Boulogne.

 

[EwenS]

Unless I am adding things up wrong the U-boats were sinking ships faster than they could be built in 1940 and 1941. The shipbuilders beat the U boats by about 17% in 1942 and it is probably true that it was in the last few months? Things may have been a bit on the iffy side at the end of 1942. Things looking better for the allies but not out of the woods yet, If Germans can get back to earlier success rates (or even close) then the surplus goes away.

The Allied introduction of new sensors and weapons means they keep the tactical initiative and the increase number of escorts just push that further.

The Germans failed to keep up the technical pace fell and behind quickly. A few extra AA guns or 20 tons more fuel oil is not really changing things by very much. They sat on the schnorkel for several years. They failed to enlarge the internal size of the boats for far too long and used those ridiculous deck storage tubes for reloads, which were pretty much useless in the North Atlantic, especially in winter. They kept a rather slow submerged speed, Under 8kts for the Type VII while the British T and U/V could make 9 and the S class could do 10kts. In a given amount of time (say 15 minutes) a boat that can do 10 kts has over 50% more "area" to disappear into than an 8 kt boat.

Please note I am not talking about new hull forms or type XXI subs.

The outcome of the Battle of the Atlantic was a lot harder to call in 1941 and most of 1942. Nov 1942 being a high point for the U-boats with 126 ships (802,160 tons) sunk. the next month saw the sinkings drop to about 1/2.

There is a difference between what we know now and what they knew then. Just a few really bad months in row would have meant real trouble but the Germans were not able to put 3 or more (or even two?) high scoring months together.

Schnorkel
The Germans weren't the only ones to sit on the Schnorkel and do nothing. Britain knew about it from at least late 1941 when the Dutch subs started to operate from Singapore and then Ceylon under British Command (see O-19 & O-20), if not from May 1940 when Dutch forces started arring in Britain. And the RN had apparently studied "underwater battery charging" pre-war. It was raised again in late 1942 when the A class were being designed. It was dropped on the ground that "submerged dieseling" had no operational value to British submarines "presumably because neither the German nor the Jpanese had effective airborne sea search radars to threaten submarines at night. Late in the war the the idea was revived, and plans were made for depot ships in the Far East to fit snorkels ('snorts' in British parlance) if necessary." (Friedman "British Submarines in Two World Wars")

And the Schnorkel had a major problem - it slowed the deployment speed of a U-boat from a decent surface cruising speed to a 6 knot at most crawl. So U-boats could spend less time in the operational area.

The Schnorchel - Technical pages - German U-boats of WWII - Kriegsmarine - 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. Over 40.000 pages on the officers, the boats, technology and the Allied efforts to counter the U-boat threat.

www.uboat.net

Underwater speed
First a correction. The only British S class with an underwater speed of 10 knots were the 12 pre-war built subs, completed 1934-38. The wartime boats of this class, ordered from Jan 1940 and completed from March 1942) could only do 9 knots submerged. And they could only run at that speed for 1.25 hours which only gets you about 11 miles away from your target before you have to surface to recharge your batteries, thereby making yourself a sitting target. And that assumes that you had a fully charged battery to begin with, which was unlikely given a submerged approach if the attack is in daylight. The RN were however happy to see that underwater speed reduced to 8 knots in the A class of 1943.


S class submerged endurance 120 nm @ 3 knots.
T class (1943 spec) 126 nm @2.25 knots
U class 120 nm @ 2 knots.
A US Gato could run underwater for 48 hours on a full battery charge. But that was at a speed of only 2 knots = 96 nm

Underwater speed was not nearly as important in WW2 as you seem to believe. All navies preferred to sneak away at low speed and increasing depth if necessary to remain undetected. That way they might be able to come back for a second bite at the cherry. A dived sub could not generally outrun a surface escort in most sea conditions. One reason why the RN escort classes had a minimum speed of 16 knots at the start of WW2, increasing later. Also a sub of that era travelling fast underwater generated a lot of noise, rendering it more detectable on ASDIC / Sonar. And running at high underwater speeds burned through the available battery power VERY fast (see above for the S class).

Type XXI
The purpose of the latger battery capacity and higher underwater speed of a Type XXI as the Germans saw it when it was being developed, was not to increase the max speed to allow escape after an attack, but to increase the underwater cruising speed, so reducing the transit times to the operating areas, and only surfacing if the weather was too bad to Schnorkel. Some comparitive date from Showell's "Hitler's 'Wonder' Boats". Type IXC v Type XXI Speed / range

Surface fast - 18.3knots / 5000 nautical miles v 15.6 knots / 5,100nm
Surface cruising - 10 knots / 13,450 nm v 10 knots / 15,500 nm
Submerged max - 7.3 knots v 17 knots
Submerged fast - 4 knots / 63 nm v 10 knots / 110 nm
Submerged cruising - 2 knots / 128nm v 5 knots / 340 nm.

This way they reckoned a Type XXI could travel 160 nm submerged each day at 7 knots with 4 hours schnorkelling and runnning the diesels burning just 2 tons of fuel while crossing the really dangerous Bay of Biscay. It could then cruise at 10 knots burning just 3.5 tons per day.

A Type IXC would need 12 days to travel submerged from Lorient 720 nm to 20 degrees west and 38 days on the surface to travel the 3,800 miles from 20 degrees west to Panama. A Type XXI would reduce that to 5 and 23 days respectively.

 

[SaparotRob]

Schnorkel
The Germans weren't the only ones to sit on the Schnorkel and do nothing. Britain knew about it from at least late 1941 when the Dutch subs started to operate from Singapore and then Ceylon under British Command (see O-19 & O-20), if not from May 1940 when Dutch forces started arring in Britain. And the RN had apparently studied "underwater battery charging" pre-war. It was raised again in late 1942 when the A class were being designed. It was dropped on the ground that "submerged dieseling" had no operational value to British submarines "presumably because neither the German nor the Jpanese had effective airborne sea search radars to threaten submarines at night. Late in the war the the idea was revived, and plans were made for depot ships in the Far East to fit snorkels ('snorts' in British parlance) if necessary." (Friedman "British Submarines in Two World Wars")

And the Schnorkel had a major problem - it slowed the deployment speed of a U-boat from a decent surface cruising speed to a 6 knot at most crawl. So U-boats could spend less time in the operational area.

The Schnorchel - Technical pages - German U-boats of WWII - Kriegsmarine - 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. Over 40.000 pages on the officers, the boats, technology and the Allied efforts to counter the U-boat threat.

www.uboat.net

Underwater speed
First a correction. The only British S class with an underwater speed of 10 knots were the 12 pre-war built subs, completed 1934-38. The wartime boats of this class, ordered from Jan 1940 and completed from March 1942) could only do 9 knots submerged. And they could only run at that speed for 1.25 hours which only gets you about 11 miles away from your target before you have to surface to recharge your batteries, thereby making yourself a sitting target. And that assumes that you had a fully charged battery to begin with, which was unlikely given a submerged approach if the attack is in daylight. The RN were however happy to see that underwater speed reduced to 8 knots in the A class of 1943.


S class submerged endurance 120 nm @ 3 knots.
T class (1943 spec) 126 nm @2.25 knots
U class 120 nm @ 2 knots.
A US Gato could run underwater for 48 hours on a full battery charge. But that was at a speed of only 2 knots = 96 nm

Underwater speed was not nearly as important in WW2 as you seem to believe. All navies preferred to sneak away at low speed and increasing depth if necessary to remain undetected. That way they might be able to come back for a second bite at the cherry. A dived sub could not generally outrun a surface escort in most sea conditions. One reason why the RN escort classes had a minimum speed of 16 knots at the start of WW2, increasing later. Also a sub of that era travelling fast underwater generated a lot of noise, rendering it more detectable on ASDIC / Sonar. And running at high underwater speeds burned through the available battery power VERY fast (see above for the S class).

Type XXI
The purpose of the latger battery capacity and higher underwater speed of a Type XXI as the Germans saw it when it was being developed, was not to increase the max speed to allow escape after an attack, but to increase the underwater cruising speed, so reducing the transit times to the operating areas, and only surfacing if the weather was too bad to Schnorkel. Some comparitive date from Showell's "Hitler's 'Wonder' Boats". Type IXC v Type XXI Speed / range

Surface fast - 18.3knots / 5000 nautical miles v 15.6 knots / 5,100nm
Surface cruising - 10 knots / 13,450 nm v 10 knots / 15,500 nm
Submerged max - 7.3 knots v 17 knots
Submerged fast - 4 knots / 63 nm v 10 knots / 110 nm
Submerged cruising - 2 knots / 128nm v 5 knots / 340 nm.

This way they reckoned a Type XXI could travel 160 nm submerged each day at 7 knots with 4 hours schnorkelling and runnning the diesels burning just 2 tons of fuel while crossing the really dangerous Bay of Biscay. It could then cruise at 10 knots burning just 3.5 tons per day.

A Type IXC would need 12 days to travel submerged from Lorient 720 nm to 20 degrees west and 38 days on the surface to travel the 3,800 miles from 20 degrees west to Panama. A Type XXI would reduce that to 5 and 23 days respectively.

 

[MIflyer]

There were a number of technological innovations that helped aircraft sink or even just scare away U-boats.

First and most importantly, microwave radar, which could even spot U-boats in the dead of night and enable attacks under circumstances in which the U-boats could not spot the aircraft.

Second, better depth charges. Early in the war US depth charges could not be set to go off shallow enough to damage a U-boat that had only just submerged.

Third, the air dropped acoustic homing torpedo, which sank a U-boat on its very first action, also giving the USN the honor of being the very first military to use guided missiles in combat. The effort had the substantial additional benefit of showing the USN that there were people who could design, develop, and build torpedoes a hell of a lot better than those idiots at the USN-operated RI torpedo Factory.

Air-launched unguided rockets were useful as well, since they provided airplanes with a "broadside" comparable to a large warship. First successful use was by a RN Swordfish aircraft.

Magnetic Anomaly Detection gear enabled U-boats to be detected and attacked while they were still submerged. Some aircraft were fitted with rocket-propelled depth charges that fired so that the rockets slowed the bombs and enabled them to hit where the aircraft had been rather than in front of it, therefore closer to where the MAD gear had spotted it.

The USN's BAT radar guided fire and forget missile originally was designed to attack U-boats but by the time it became available the threat in the Atlantic had ended and so it was switched to attacking Japanese surface ships in the Pacific.

 

[SaparotRob]

There were a number of technological innovations that helped aircraft sink or even just scare away U-boats.

First and most importantly, microwave radar, which could even spot U-boats in the dead of night and enable attacks under circumstances in which the U-boats could not spot the aircraft.

Second, better depth charges. Early in the war US depth charges could not be set to go off shallow enough to damage a U-boat that had only just submerged.

Third, the air dropped acoustic homing torpedo, which sank a U-boat on its very first action, also giving the USN the honor of being the very first military to use guided missiles in combat. The effort had the substantial additional benefit of showing the USN that there were people who could design, develop, and build torpedoes a hell of a lot better than those idiots at the USN-operated RI torpedo Factory.

Air-launched unguided rockets were useful as well, since they provided airplanes with a "broadside" comparable to a large warship. First successful use was by a RN Swordfish aircraft.

Magnetic Anomaly Detection gear enabled U-boats to be detected and attacked while they were still submerged. Some aircraft were fitted with rocket-propelled depth charges that fired so that the rockets slowed the bombs and enabled them to hit where the aircraft had been rather than in front of it, therefore closer to where the MAD gear had spotted it.

The USN's BAT radar guided fire and forget missile originally was designed to attack U-boats but by the time it became available the threat in the Atlantic had ended and so it was switched to attacking Japanese surface ships in the Pacific.

 

[Frog]

Why didn't the British bomb the U boat pens while they were being built on West Coast of France? If they had bombed around the time the cement was poured it would have destroyed them.

Not enough bombers, not enough powerful bombs, good flak, not enough good aiming by night.

 

[Geoffrey Sinclair]

In theory bombing ports and minelaying in waters near Britain were more a Coastal Command duty 1939 to 1941.

Bomber Command: Lorient Minelaying operations on 22, 23 and 27 August 1940, the aircraft also carried bombs to drop on targets of opportunity, first bomb raid 2 September 12 aircraft, more mines on 17 September, next bomb raid 27 September 34 aircraft, 5 bombing aircraft on 7 October plus mine layers, and so on.

1941 effort
Bordeaux 12 tons of bombs
Brest 3,311 tons of bombs (3,226 tons on "fleet")
La Pallice 79 tons of bombs
La Rochelle 1 ton of bombs
Lorient 261 tons of bombs
Saint Nazaire 30 tons of bombs
Out of 31,740 tons of bombs dropped for the year

The bombing does not seem to have hindered the construction works at Brest.

The US Merchant Marine makes the point it had a higher percentage death rate than any of the US armed forces. The shipping losses in the 1939 to 1941 period were more than Commonwealth new construction but were offset by much previously neutral shipping becoming allied, Norway, Netherlands, Greece etc. Lloyds notes British and Neutral shipping losses in 1940 were 2,308,370 GRT to submarine, 708,102 GRT to aircraft, in 1941 2,307,010 GRT to submarine and 1,043,717 GRT to aircraft (a lot of the losses to airpower were in the Mediterranean), it was not just anti submarine defences needing improvements. In 1940 17% of total losses were of officially neutral shipping, down to 5.4% in 1941.

The further out the convoy was the greater the chances the aircraft would not find it, any radio traffic to home in the aircraft could home in the U-boats. Also though there definitely were significant convoy battles to the end of 1941, 1942 even, the reality most merchant ships lost were sailing independently. Helped by the way the Germans could often read the merchant ship code. It is also worth bearing in mind for much of the 1930's aircraft flying the Atlantic were news, operating aircraft 600 or more miles out over the ocean and return required changes in mental attitudes as well as lots of training, equipment and technique changes. Iceland weather meant being able to divert to North America if required.

Ideas on Coastal Command anti submarine strength were founded on U-boat bases in Germany, not France, the crisis of 1940 and the inevitable time to train new forces did not help. The time to create the bases in Iceland and the weather there another factor. Then comes deliberate decisions to boost the bomber strength in 1940/41, while not as long range as the B-24 the Stirling and Halifax could carry a bigger load longer than the Sunderland for example, Wellingtons proved useful for medium range operations. A good clue about aircraft was the way the U-boats kept moving out beyond air cover range. Bomber Command (mostly from an OTU) did around 2,300 anti submarine sorties in 1942 and 1943, not a lot versus the nearly 43,000 such sorties (Including over coastal shipping) flown by Coastal Command, but non zero.

RAF Liberator imports 78 in 1941 (first in March), many transports, 98 in 1942, 316 in 1943, 937 in 1944, 548 in 1945 (to end September). To end September 1943 all but 8 imports had been into the UK. The B-24 was not on Bomber Command's approved list before RCM requirements in 1944. The first non Coastal Command RAF B-24 squadrons were 159 and 160 squadrons, formed in January 1942, ordered to India they were initially held in the Middle East in June 1942. RAF Catalina imports were 88 in 1941 plus 3 to Canada and 149 in 1942, plus 6 to Canada, they were longer ranged than the Sunderlands.

For most of 1942 the need was for short and medium range airpower to patrol of the American coasts, not the convoys to Britain.

Coastal Command February 1943, on the 11th of the month there were 5 I, 1 II, 22 IIIA and 2 V Liberators, versus establishment of 40 IIIA and 12 V. On the 25th it was 5 I, 1 II, 28 IIIA and 5 V.

March 1943, 184 RAF Liberators, 58 with Coastal Command, 9 in the Middle East, 27 in India, 13 in Canada, 14 BOAC, 8 En Route from USA, 23 being modified, 14 in Ferry Pool units, 2 being assembled, the rest under maintenance etc. The USAAF had 459 B-24 overseas (including reserves) mostly as bombers and 715 in the US. To the end of March the USN had received 112 B-24 direct from production, plus some transferred from USAAF stocks.

More VLR B-24 would not have made much of a difference to sinkings until about the final quarter of 1942 given when they turned up and where the sinkings were happening, boosting Coastal Command strength pre war was required to have it ready for the 1940/41 happy time, plus increasing airpower effectiveness to locate and successfully attack. The steady increase in surface escorts, reducing the number of independent sailings and the reading of U-boat messages in the second half of 1941 were more important than aircraft strength, then came the move to the Americas. At the same time aircraft patrolling the Bay of Biscay or Scotland/Iceland barrier patrols were probably more productive than serving in Bomber Command, also of course having VLR units in service in 1941 gained vital experience to benefit later operations.

North Atlantic convoys paid a price for Operation Torch, while the release of many anti submarine assets after the initial invasion and reinforcement period played a part in the change of fortune in the North Atlantic.

More resources usually help, the more air patrols U-boats had to face in transit from their bases to the North Atlantic the more efficiency reductions, range also matters as the further offshore the U-boats were pushed reduced their efficiency, but patrolling the open ocean looking for U-boats without aids like code breaking is a waste, making convoys safer much better but again it is remarkable how few ships were lost from convoys in both absolute and percentage of loss terms until the second half of 1942. Bomber Command was less efficient than Coastal Command at least until some time into 1942, giving "painless" what if scenario resources to switch. Yet it comes back to reducing independent sailings and code breaking enabled evasion mattered more than anything other than a major boost in aircraft (mostly barrier patrol) capabilities until the second half of 1942.

I am equivocating because the answer is not simple. Sort of like giving Bomber Command a Lancaster force in January 1941, of itself unlikely to improve overall outcomes in 1941 but setting things up for a better 1942. Any early war loss that does not occur is a ship and crew available for years of service. The shipping constraints meant amphibious shipping constraints and both restricted allied capabilities. The big merchant ship losses in 1940/41 were before the 4 engine types turned up and were part of a crisis for the British that prevented many responses, the best chance of aircraft doing anything would be transferring 4 group to Coastal Command pre war instead of the temporary attachments of Whitley squadrons 1940/41. The crisis of much of 1942 was out of Coastal Command's area and in coastal waters. The final North Atlantic crisis required long range airpower, or short range operating off carriers sailing with or near the convoys. HMS Courageous was sunk and Ark Royal near missed on anti submarine patrols in 1939, would escort carriers do any better? HMS Audacity did not last very long.

Another post battle lesson, concentrate on building escorts early instead of merchant ships.

 

[Shortround6]

Trouble was that they had forgotten or ignored the lessons of 1917-1918.

the more air patrols U-boats had to face in transit from their bases to the North Atlantic the more efficiency reductions, range also matters as the further offshore the U-boats were pushed reduced their efficiency, but patrolling the open ocean looking for U-boats without aids like code breaking is a waste, making convoys safer much better but again it is remarkable how few ships were lost from convoys in both absolute and percentage of loss terms until the second half of 1942.

Both points had been proven in WW I. Just on a somewhat smaller scale.
Also without good aerial recon and/or radio traffic interception The U-boats were patrolling the open ocean looking for convoys (or independent ships) and without radar, subs have a rather limited search range even in good weather on the surface.

In the last 18 months of WW I merchant ships made 84,000 voyages in convoy. Of those 257 while they were in convoy. Out of the 257 only two had been lost while the convoy enjoyed both surface and air protection. This may skew things to the aircraft in that in WW I the aircraft were not operating far from shore (only the last day or two of the voyage depending on ports) and many of sinkings were further out from port/airfields so 100% accurate comparison cannot be made.
During the war (WWI) more importance than was warranted was placed on interdicted the subs in the transit areas as a result of kill 'claims'. There were 5 claims. Only one of which turned out (?) to be a real kill. A few boats may have been damaged but not killed.
4 boats had been killed by combined aircraft/surface ship attack near convoys by convoy escorts. Given the anti-sub armament of the vast majority of aircraft in 1917-18 not much more could be expected. The actual killing was done by the ships. The finding/fixing was the contribution of the aircraft.

They had a system that worked. They knew why it worked. It should have worked better with (maybe not a lot) with better armament, better ranged aircraft (compared to WW I) and with better signals (1939 radios).
But the strategy in 1938-39-40 was to bomb the U boats in the yards/docks and let the RN sort out the ones at sea while the BC stopped the supply of new boats.

Granted the 1939-42 U-boats were better than the WW I U-boats, but how much better? Speed, range, radios, etc.

 

[Shortround6]

Underwater speed was not nearly as important in WW2 as you seem to believe. All navies preferred to sneak away at low speed and increasing depth if necessary to remain undetected. That way they might be able to come back for a second bite at the cherry. A dived sub could not generally outrun a surface escort in most sea conditions. One reason why the RN escort classes had a minimum speed of 16 knots at the start of WW2, increasing later. Also a sub of that era travelling fast underwater generated a lot of noise, rendering it more detectable on ASDIC / Sonar. And running at high underwater speeds burned through the available battery power VERY fast (see above for the S class).

A lot of this is true. But even a few minutes at a higher speed can be an advantage. 3 minutes at 9kts gets you 3 times further away from the data point (submerge point) than 3 minutes at 3 kts.
A lot depends on situations. Subs often depend on speed for fast diving, water flow over the hydroplanes can give faster results than trying to flood tanks, especially during initial stage of diving while the crew is still working on the exact balance/buoyancy of the boat.

Fast moving escorts cannot listen well. So a fast moving sub, making noise, can sometimes throw off a pursuer by slowing down and changing course. The change in sound may give the illusion of the sub moving further away than it is. Or cause the pursuer to also slow down and see if he can regain contact.
Now hydrophones and sonar/asdic all changed during the war so things changed a lot. Early Sonar/Asdic did not have a lot of range and it helped a surface ship to close range to the contact point fairly rapidly to get into effective Sonar range. There are two ranges, the active sonar pulse and the passive listing which is often greater but highly dpendend on the nosie the target is making. The flip side of the that was that high speed also deafened the hunting ship until it slowed down. This is one reason that ships later hunted in pairs or trios. One or two ships stood off and fixed (located) the target while the "killer" made the higher speed attack run. It needed some speed to keep from blowing itself up with shallow depth charges.

With a lot of the early depth charges they needed to get the charges within 25-30 feet for a kill and into the 30-40 ft range for damage. Deep subs result in long time delay. British 1939/40 depth charges sank at 7ft/sec initially and reached 9.9ft/sec at 250ft.


As far as the Batteries for Subs goes, most lead/acid batteries show similar discharge curves.
The battery does not give up the same power at high draw rates as it does at low rates. That is to say that the power (amp hours) falls off considerably as the power consumption increases. Most car/commercial batteries are 'rated' at a 20 hour draw rate. The battery will give you over 10 times the power but it lasts for a very small fraction of the time. More like 5% instead of 10% for 10 times the power so power management of sub batteries was very important.
But then we get into design, If boat got it's extra knot or two from good streamlining or lack of external lumps (extra guns?) maybe it's mid range speed (5-6kts) saw an improvement in endurance? If a boat just shoved in higher power motors (higher power consumption to begin with) then maybe there was no increase in endurance at the lower speeds, unless, the newer version of the boat got newer/larger batteries.

But just like a fighter plane does not fly at full throttle for full hour, a faster sub may have options open to it that a slower sub does not, even if it is for just a few minutes.

 

[pinehilljoe]

In the end the Germans did not come close to blockading England. In all, during the Atlantic campaign only 10% of transatlantic convoys that sailed were attacked, and of those attacked only 10% on average of the ships were lost. Overall, more than 99% of all ships sailing to and from the British Isles during World War II did so successfully.

If you are selling books, its more exciting to write about how close a thing it was. This no way takes away from the suffering and loss of thousands of people on both sides. The Battle of the Atlantic was horrible, the whole damn War was horrible.