You asked Drgondog, so here is the British plan (in some detail!!!)
So how does the UK survive the war without the US?
Glider has already mentioned the first point,
#1
The UK needed to put far more effort into command of the oceans using long range A/S patrols.
I would take it a step further, do as the Army Navy (Brooke Pound) had proposed, that Coastal Command and Army air support be taken from the RAF, just as the Fleet Air Arm was taken from the RAF in 1937.
The problem was that all of the top RAF brass (Newall, Portal, Harris) were all followers of the "Trenchard Doctrine" which believed that the war could be won with only a heavy-bombing campaign, which later proved to be wrong. There were earlier reports of the lack of results, and a comprehensive study (Butt report) in Aug 1941 showed that over the Ruhr only 10% of the bombers hit within FIVE miles of their targets! Since the top RAF brass controled development production, the lion's share went to Bomber Command Fighter Command, but there was not nearly enough effort made in providing army support, and Coastal Command had to get by on hand-me-down aircraft. (Whitley's, Hampden's etc.)
Thanks to Glider for his earlier excellent post!
In my earlier postings I outlined the basis on which I believe this could have been achieved. By diverting the long range aircraft to A/S warfare, losses would have significantly reduced to acceptable levels.
The 50 old destroyers were of some benefit but has been pointed out they were old, unreliable and needed a lot of maintanence and updating. 50 long range aircraft would have been of more benefit and tragically were available but not released by bomber command. The aircraft used in Coastal Command at the time were obsolete bombers, Whitley, Hampden plus Hudsons and a few Wellingtons.
Those that could have been used are Sterlings and Halifax's.
#2
Complete the rail network in Africa Arabia to Russia
This is probably one of the most overlooked solutions.
From June 1940 - June 1943 the British could not use the Mediterranean and were forced to go around the cape of South Africa. This used up an extra 1 - 2 million tons for the longer journey. In 1941 the German submarines started to suffer high losses in the North Atlantic, so they moved to more fruitful distant areas, like the S. Atlantic. The British would have done well to eliminate all excess shipping routes by using rail instead.
I propose that in 1940 after the Battle of Britain the British realize that they cannot count on any US support, so they start making plans to maintain communication, by linking their Empire rail systems.
The best option to reduce shipping is to link the Nigerian rail network with the one in Egypt/Sudan, by building 1,100 miles of track across Chad, from Ft. Lamy to Egypt. (Chad is in Free French control, from Aug 1940) I would also finish the last 500 miles of the Cairo - Capetown railway to link up with the South African system. From my information, a railway party of 50 - 60 men with horses can build 3 - 5 miles per day over normal terrain. 8 or 10 such parties could finish the track in about 2 - 3 months. This would allow for the elimination of the "round the cape route", the cargo would off-load in Nigeria or Cameroon, and men, tanks planes could be sent to Egypt, oil would be transported the other direction. Canada S. Africa could supply the equip + skilled labour, with surplus track from Namibia, Botswana etc.
I would also complete the 600 miles of Baghdad - Beirut railway through Jordan to Persia. This would give a rail link from Nigeria through Egypt Persia to Russia, allowing the elimination of the costly Murmansk convoys, as supplies could be sent much more quickly by rail. (the Allies did send the greatest % of lend-lease through Persia in 1942-1943)
#3
Reduce the number of convoy routes, but increase their protection
The British would then move all goods by rail, except 3 heavily protected convoy routes (+ 1 aux) Each waypoint on the routes would have an airbase operating a squadron (or more) of long range A/S patrols (except Hawaii). None of the legs are more than 800 - 900 miles from an airbase, except the two from Guiana, S. America to Gambia, Africa (2500 miles) and Vancouver - Fanning Isl. which is about 3500 miles. So the longest A/S patrol would have to be 1,300 miles (No sub activity expected (Vancouver - Fanning)
Route 1 UK Liverpool - Iceland - Greenland - St. John's - Montreal
Route 2 Halifax - Bermuda - Virgin Is - Trinidad - Guiana - Gambia - Nigeria
Route 3 Bombay - Ceylon - Sumatra - Java - Perth - Adelaide - Auckland
(Aux) 4 Vancouver - (Hawaii) - Fanning - Tahiti - Tonga - Auckland - Sydney
I would calculate that in 1942 the concentration of shipping routes, + the increased A/S patrols, + elimination of Murmansk convoys should reduce the losses from U-boats by at least half, to under 2 million tons. This would almost match the Commonwealth construction (1.8 million tons in '42) Even if the British lose 3 million tons in 1942 and in 1943 they are STILL ahead of their pre-war total. With the reduction in the # of shipping routes they have surplus capacity.
In answer to your question about Allied shipping Drgondog, the British Allied shipping losses in '39 - '41 were about 5.3 millon tons, while the UK/Commonwealth built about 2.6 millon tons '39 - '41. However the British also picked up about 5.6 million tons, mainly from the Norwegian Dutch merchant marine. So by Dec 1941 they are actually 3 million tons
ahead of when they started the war.
Thanks for the info AL Schlageter
Got this off some BB somewhere, sometime.
1939:
Allied and Neutral ship tonnage sunk by German and Italian submarines 509,321 tons (127,330.25/month)
British merchant ship construction capacity from 1939-1941 did not exceed 1.2 million GRT per year.
1940:
Allied and Neutral ship tonnage sunk by German and Italian submarines 2,462,867 (205,238.91/month)
Thus for 1940, an average of 3.77 ships were sunk per patrol and one U-Boat was lost per 28.89 ships sunk.
1941:
Allied and Neutral ship tonnage sunk by German and Italian submarines 2,298,714 (191,559.5/month)
Thus for 1941, an average of 1.59 ships were sunk per patrol and one U-Boat was lost per 18.28 ships sunk.
1942:
# Ships/tonnage
Allied and Neutral ship tonnage sunk by German and Italian submarines 6,158,473 (513,206.08/month) {2 million US + 4 million Allies}
British and Canadian merchant ship construction 1942 1.8 million GRT
US merchant ship construction 1942 5.433 million GRT
Thus for 1942, an average of 2.14 ships were sunk per patrol and one U-Boat was lost per 16.99 ships sunk.
1943:
Allied and Neutral ship tonnage sunk by German and Italian submarines 2,510,304 (209,192/month)
So, overall, the most successful year for the U-Boats was 1940, before the expansion of the force allowed for an increase of more than about a dozen patrols sailing per month, and well prior to the entry of the US and its shipbuilding capacity into the war. Worse, the performance of the U-Boat force in 1941 and 1942 never exceeded its performance in the first months of the war. And, after 1943 the U-Boat campaign became ever less relevent to the outcome of the war.
U-Boat Fleet to 1 Sep 42
On 19 Aug 39 there were 57 U-Boats in commission
Total number U-Boats deployed to 1 Sep 42 275
Total number lost 94
Total number retired 10
Total number available 171
U-Boat Fleet '42 to '45
Total number deployed 1 Sep 42 to 1 May 45 531
Total number lost 1 Sep 42 to 1 May 45 568
British controlled merchant shipping over 1,600 GRT (gross tons)
3Sep39 17,784,000
30Sep40 21,373,000*1940 add 5.6 million tons Dutch/Norw*
30Sep41 20,552,000
31Dec41 20,693,000
Thus, despite the 'success' of the U-Boat force in 1940 (relative to its performance in 1941 and 1942) it had no appreciable effect in reducing the size of the British merchant fleet.
So that is what I calculate is the best solution to the Shipping/U-boat problem, next I'll post the British Military strategies