The shipping shortages were persistent, even as late as 1945 Churchill made it clear the British Pacific fleet size started with firstly removing the shipping needed for UK imports, not with the number of warships available. In terms of range the further out from shore convoys can expect air or surface escort cover the further out the U-boats have to operate and so reduce their effectiveness. Coastal Command had around 250 aircraft in September 1939, 200 of which were short range, basically Ansons. At the end of 1941 it had around 400 aircraft, only 18 of which were considered short range.
The Cost of Seapower by Philip Pugh, his theoretical model says the break even number of escorts per convoy was 10, which would normally give a ratio of 1 submarine sunk per 5 merchant ships, which meant both sides lost an equivalent monetary amount of ships. Going to 14 escorts near doubles the kill ratio in favour of the defenders. If there are only 2 escorts the chances of a submarine being sunk are effectively nil. Overall he says the ratio of submarines to merchant ships sunk is proportional to the square of the number of escorts.
The RN calculated in 1942 that each U-boat sunk saved 4.8 merchant ships because it took the Germans 6 months to train a new U-boat crew. In the second half of 1942 long range anti submarine aircraft operations were calculated to save the following number of merchant ships per 100 sorties.
Continuous Convoy Escort, 3
Bombing U-boat bases, 1
Bay of Biscay patrols, 3
Escort of convoys known to be under attack, 30.
In 1940 to 1943 the HX convoys consisted of 7,285 ships of which 77 were lost in convoy, 46 while straggling and 34 after being detached or the convoy dispersed. The SC convoys had 4,251 ships, lost 115 in convoy, 41 stragglers and 12 after being detached or the convoy dispersed. According to the RN official history from January 1942 to May 1943 inclusive 537 ships were sunk in convoys (411 to subs), versus 1,067 ships sailing independently (934 to subs). Even in the first 5 months of 1943 the convoys lost 193 ships versus 105 sailing independently. It looks like the U-boats only sighted a minority of convoys in the Atlantic and converted about half the sightings into attacks on the convoy.
U-boat numbers went from 56 pre war to 50 by the end of 1939, bottomed out at 45 in April 1940, were 82 by the end of 1940, 244 by the end of 1941, 407 by the end of 1942, 471 by the end of 1943, 467 by the end of 1944. At the end of 1939 some 35 U-boats were front line, the rest were working up or training boats, at the end of 1940 there were 22 front line boats, end 1941 91, end 1942 213, end 1943 around 160. (From Germany and the Second World War volumes V part 1 and part II and volume VI). According to the RN Official History 9 U-boats were sunk in 1939, 24 in 1940 (including U-32 sunk twice), 35 in 1941, 87 in 1942, 237 in 1943, 242 in 1944 and 151 in 1945.
UK merchant ship building had dropped to around 133,000 GRT in 1933, had risen to 500,000 GRT in 1935, 920,000 in 1937. A major driver of new merchant ship construction was how much was laid up, in 1932 around 4.4 million GRT, in 1932 13.6 million, in 1935 5 million, in 1937 1.7 million, in 1938 2.3 million. The production by the US of dry / US all cargo ships / UK all cargo ships by year in GRT was
1939 121,000 / 242,000 / unknown
1940 301,000 / 449,000 / 810,000
1941 546,000 / 768,000 / 1,156,000
1942 4,571,000 / 5,247,000 / 1,301,000
1943 9,803,000 / 12,309,000 / 1,204,000
1944 6,859,000 / 9,703,000 / 1,014,000
1945 4,231,000 / 6,714,000 / 512,000 (UK to end September)
Canada figures are in deadweight not gross tons, dry cargo only, yearly 1941 to end August 1945, 10,000, 843,000, 1,370,000, 981,000, 315,000 DWT (US WPB report, US Maritime Commission says its 1939 to 1945 production in GRT was 71% of the DWT figure). US production exceeded UK production in the first quarter of 1942, US data from the Maritime Commission Summary report, the UK figures from the UK statistical digest of the war.
The Kriegsmarine lost 23 U-boats to the end of April 1940. Those early allied successes had a hidden bonus, most of the crews were lost to Germany and contained mainly pre war regulars, the cadre for the expanded fleet. In exchange for the losses the U-boats had sunk some 751,877 GRT of shipping (including ships of neutral countries) according to Lloyds, maybe around 770,000 GRT when you add in the ships "Axis Submarine Successes" lists but Lloyds mark as unknown. So around 33,500 tons per sunk boat, and around 96,000 GRT sunk per month, but that figure includes neutral shipping, allied shipping lost comes to 454,950 GRT, maybe 460,000 GRT with the unknowns included. The ratio is then 20,000 GRT per U-boat loss and 58,000 GRT per month for allied merchant shipping alone. (In 1944 submarines sank around 60,000 GRT per month, and in the first 4 months of 1945 71,000 GRT per month of allied shipping). The invasion of Norway in April 1940 curtailed the U-boat war against commerce for a while as the U-boats were deployed to try and protect the invasion. This is where the faults with the German magnetic torpedoes were exposed, another fault with the contact exploder was rectified by using the RN design, a more subtle fault was not discovered until much later, the atmospheric pressure in the U-boat, which rises with the length of time submerged, effected the torpedo depth setting. Between 1 May 1940 and 1 March 1941 the Kriegsmarine would lose 10 U-boats and sink 2,102,027 GRT of shipping according to Lloyds, plus maybe around 150,000 GRT more if Axis Submarine Successes is correct, or around 10 times the exchange rate of early in the war. In June 1940 the number of front line boats dropped to 27, after starting at 39 and staying above 30 until that time, during June allied losses to U-boats were 269,119 GRT. The number of front line boats stayed at 30 or below for the rest of the year, allied losses July to December 1940 were 1,246,841 GRT, over 200,000 GRT per month.
Front line boat strength increased to 38 in July 1941, so back to the opening of the war strength. By December 1941 front line strength was 88 (out of 236 boats available). Diversions to the Arctic and Mediterranean started in August 1941 and by December 5 boats were in the Arctic and 23 in the Mediterranean. Even so the number of boats in the Atlantic in the second half of 1941 was around twice that of the first half of the year. Losses to U-boats January to June 1941 1,317,268 GRT, July to December 676,298 GRT. In the 6 month time period July to November 1941 the sinkings of allied ships by U-boats had declined to their lowest levels since the defeat of France, according to Lloyds around an average of 140,000 tons per month versus 210,000 tons per month in the first 5 months of 1941. In the North Atlantic where over 90% of the U-boat successes were according to the RN November and December 1941 losses were a little under 101,000 tons. This was due to a combination of more and better escorts, diversions of U-boats to the Baltic, Arctic and Mediterranean, intelligence (including Ultra), raising the speed at which a merchant ship could sail alone and the US exclusion zone. (I am ignoring the Mediterranean and Arctic boats since they had few merchant ship targets). U-boat losses (all causes) were some 12 in the first 6 months of 1941 and 25 in the second 6 months, so the escorts were improving as well. The U-boats in the second half of 1941 were running at about 1/4 the productivity of the first half and the cost per merchant ton sunk had increased by a factor of 8. On the basis of the performance in the second half of 1941 the Germans were not going to starve out Britain quickly, but nor were the British building the surplus merchant ships needed to keep a large military fighting on distant shores.
During 1941 the tonnage sunk per boat day at sea for the Atlantic boats peaked at 637 in February, it then declined to 66 in August (the big drop was from 314 in June to 73 in July) picked up to 190 in September but was down to under 100 in November and December. It jumped to 223 in January 1942 and kept above 200 before rising to 301 in May and peaking at 341 in June, then largely staying between 150 and 200 until November, declining to 96 in December.
From the USN official history, "knowing that a convoy without adequate protection is worse than none, Admiral Andrews decided that convoys were then inadvisable. But on 1 April a partial convoy system was inaugurated whereby ships were moved by anchorage to anchorage escorted by such local craft as were available in the various Naval Districts under the direction of Commander Eastern Sea Frontier." If I read this correctly the USN believed it was best to avoid convoys unless they were "adequately protected". This is contradicted by the WWI and 1939/40/41 experiences.
A factor hampering early allied efforts was the initial refusal to believe the U-boat tactics of night surface attacks. While U-boats operated independently there was little information for allied tracking to work from, wolf pack tactics changed that, a risk Doenitz had accepted. Experience and an expanded direction finding network then enabled forecasts to be made of U-boat movements. Next came Ultra following successful operations February to June 1941, when the U-boats went over to their own version in 1942 the surface ships that escorted them in and out of ports stayed on the old version which remained largely readable. This at least enabled reasonable tracking of numbers at sea. While regular photographic coverage of German ports etc. enabled accurate tracking of new construction and training progress regardless of any Ultra information.
Coastal Command mainly Anti Submarine aircraft 1939 to 1942, Anson, Battle, Canso, Catalina, Fortress, Halifax, Hudson, Lancaster, Lerwick, Liberator, London, Northrop, Stranraer, Sunderland, Tiger Moth, Ventura, Wellington, Whitley, of these the overlap with Bomber Command was Halifax, Lancaster, Ventura, Wellington, Whitley
1939 to 1942 hours flown per year, first list 23,885, 113,942, 98,177, 141,473 of these the Bomber Command types flew 0, 1,721, 19,309, 43,526. Meaning doubling the Bomber Command types activity in 1941 would give around another 20% patrol time, in 1942 around 31% more. Bomber Command flew around 180,000 operational hours in 1942, including Blenheims etc. end of February 1942 it had 2 Halifax squadrons, nominal strength 32 aircraft, 27 serviceable 17 of them had a crew. Wellingtons were 264 authorised strength, 197 serviceable aircraft with crews, Whitley 88 authorised strength, 41 serviceable aircraft with crews. Along with 6 serviceable Lancaster with crews, 25 serviceable Stirling with crews. As of 1 March 1942 Coastal Command (no crew data available) had 6 serviceable Wellingtons, 25 Whitley, 4 B-17 and 9 B-24. Strength wise Coastal Command had 15 four engine land types and 24 Sunderlands, Bomber Command units if at full strength had 128 four engine types.
1 January 1943, Coastal Command had 118 land based 4 engine types and 81 Sunderlands, Bomber Command had 163 Halifax, 246 Lancaster, 54 Stirling, total 463. The losses Bomber Command was taking suppressed the growth of itself and Coastal Command.
So how much of Bomber Command is transferred?
As I am sure everyone is desperate to know in 1939/40 Tiger Moths flew 2,815 sorties taking 4,567 hours, no losses recorded.
I read once a quote attributed to the Botha that says it all. In a test report, the pilot wrote "Access to the cockpit is difficult, it should have been made impossible..."
