AHC: Most succesful British submarine force possible in WW2?

It was ordered in the 1935-36 Estimates. See below:
1923-24 ― 1 O class
1924-25 ― 2 OA class
1925-26 ― none
1926-27 ― 6 all O class
1927-28 ― 6 all P class
1928-29 ― 4 all R class
1929-30 ― 3 - 1 Thames class and 2 S class
1930-31 ― 3 - 1 Porpoise class and 2 S class
1931-32 ― 3 - 1 Thames class and 2 S class
1932-33 ― 3 - 1 Thames class and 2 S class
1933-34 ― 3 - 2 Porpoise class and 1 S class
1934-35 ― 3 - 1 Porpoise class and 2 S class
1935-36 ― 3 - 1 Porpoise class, 1 S class and 1 T class
1936-37 ― 8 - 1 Porpoise class, 4 T class and 3 U class 4 3
1937-38 ― 7 - all T class
1938-39 ― 3 - all T class
1939-40 ― none - 4 T class were planned, but they hadn't been ordered by September 1939
X1 was built under the 1922-23 Estimates IIRC and IIRC scrapped under the age clause of the First London Naval Treaty that set the service life of a submarine at 13 years. IIRC before that the Admiralty had set the service life of a submarine at 10 years, but don't quote me on that.

Under the Rearmament Programme 7 submarines should have been ordered in 1938-39 and 7 more in 1939-40 but the strain rearmament put on the economy forced a reduction to 3 submarines in 1938-39 and 4 in 1939-40 which as far as I can ascertain were included in the 24 submarines ordered in the War Emergency Programme.

In the early 1920s the plan was for a force of 80 submarines to be built at a rate of 8 per year, but HM Treasury, Parliament and the Cabinet would only allow a rate of 6 per year, but the Depression and 1st LNT reduced that to 3 per year for 1929-30 to 1935-36. The "Two Power Standard" reintroduced in the second half of the 1930s to provide the UK with a fleet capable of fighting German and Japan at the same time required a fleet of 82 submarines to be built at a rate of 7 per year.
Of the above:
  • The 8 submarines in the 1936-37 Programme were completed between August 1938 and October 1940. However, the last to be completed was HMS/M Thunderbolt (formerly Thetis) and the seventh to be completed was Tribune in October 1939.
  • The 7 submarines in the 1937-38 Programme were completed between July 1939 and August 1940.
  • The 3 submarines in the 1938-39 Programme were completed between February 1940 and January 1941.
24 submarines were ordered in the 1939 War Emergency Programme. They consisted of 5 S, 7 T and 12 T class boats. They were completed between August 1940 and December 1941.

54 submarines were ordered in the 1940 War Emergency Programme, but 10 were cancelled. The 44 that were completed consisted of 13 S class, 9 T class and 22 U class. They were completed between April 1941 and October 1943.

ITTL

IMHO the only way to have a more successful submarine force is to make it larger.

With hindsight submarines should have been ordered at the rate of 8 per year in the 4 building programmes from 1936-37 to 1939-40. That is a total of 32 submarines instead of 18.

The 6 extra submarines ordered under the 1937-38 to 1938-39 programmes would probably be extra T class boats and complete between July 1939 and January 1941.

The 8 submarines in the 1939-40 programme would be ordered in the Spring of 1939. Again I think they would probably be T class boats and they would effectively be the 7 boats (plus one ) in the OTL 1939 WEP brought forward by 6 months, which would advance their completions from May 1941 to August 1942 IOTL to November 1940 to February 1942 ITTL.

However, the number of submarines ordered in the 1939 WEP would be reduced from 24 to 16 boats ITTL.
 
An ASW submarine requires homing torpedoes. Straight-runners haven't got a chance because a sub moves in three dimensions. A submerged sub has been sunk by another submerged sub only once in all history, even given the availability of homing torpedoes late in the war.

So a critical part of the OP's challenge is intensive research into torpedoes, including live testing. The RN needs, first and foremost, a torpedo that works properly and explodes when it's supposed to. It also needs a homing torpedo ASAP and preferably pre-war, if ASW subs are desired. ASW subs would also need to be faster than their enemies while submerged. Supposing that the RN's resources are limited, I'd scratch the aircraft carrier subs and spend the money on researching torpedoes.

I agree minelaying and special forces insertion/extraction are good tasks to assign to submarines. If mines are laid by a submerged sub rather than a ship that can be observed, you find out the area is mined when you lose a ship. As for special forces, there were a few times during the war where being able to land a strong commando force would have made a strategic difference. Unlike WW2 paratroopers, you can be confident that a sub will deliver the men as a unit and at the desired point.

I'm thinking about the port of Cherbourg. Send in a flotilla of subs with commando teams, seize the port and prevent the Germans from destroying the infrastructure -- that makes Antwerp less of a critical objective and makes resupply and reinforcement after D-Day so much easier.

Not exactly.

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Turnaround by Red Ball Express thanks to the "genius" who chose the wrong kind of trucks which konked out necessitating borrowing trucks from the other ally, slowing both armies down; botched Caen; botched clearing the channel ports and chose Market Garden instead of clearing Antwerp; meant a 2 week run from Cherbourg a port (cleared by the Americans) all the way to the Allied forward lines. Everyone was starved for gas and bullets. Submarines do nothing to change that outcome.

Antwerp to Horrocks was three days.

Better generalship or someone who could read a map might have changed that adverse outcome. It's a difference of 700 kilometers.
 
Since the topic is the better British submarine service for WW II, let one address that issue.

First, no outlandish extrapolations. The British have limited resources to assign. ASW is the highest naval priority, fleet readiness the second highest, fleet air arm next, and on down the line so in any ATL that is even plausible, the subs will come just ahead of the RN ice cream budget.

Given the low priority, the mission drives the need.

Two viable operational theaters. Pacific (lower priority) Mediterranean (higher priority).

British Med boats look to be the U and V classes. Expect these boats to be slaughtered., The Italians are GOOD at ASW.

These boats desperately needed better induction valves, thicker pressure hulls, a working acoustic soda can decoy system, depth control arrangements, electric motor and screw silencing, a dived camouflage scheme, and better tender support services for when they came in damaged after a patrol.

Nothing wrong with the crews or their skippers. The British are one up on both the Germans and Americans there at the war's start.

The T-class and others like them appear tailored for the Pacific.

Gawdawful boats. They and the A class which followed them, seem to have been designed to kill their crews. Once again, silenced electric motors, better induction valves and simpler dive controls would have helped.

British construction methods and workmanship seems to have been a problem in any of their submarines, so one critical area has to be quality control of manufacture.

The British were not alone in this last issue. American shipyards and GOAT ISLAND naval torpedo station in the 30s and early 40s killed several hundred US submarine sailors in WW II due to their incompetent workmanship and inadequate quality control.
 
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Not exactly.

C_Plan_14.png


Turnaround by Red Ball Express thanks to the "genius" who chose the wrong kind of trucks which konked out necessitating borrowing trucks from the other ally, slowing both armies down; botched Caen; botched clearing the channel ports and chose Market Garden instead of clearing Antwerp; meant a 2 week run from Cherbourg a port (cleared by the Americans) all the way to the Allied forward lines. Everyone was starved for gas and bullets. Submarines do nothing to change that outcome.

Antwerp to Horrocks was three days.

Better generalship or someone who could read a map might have changed that adverse outcome. It's a difference of 700 kilometers.

There was plans to move part of the Mulberries along the coast but the sudden massive advance of 21st Army group that went from the Seine to Antwerp in 4 days put that idea on hold

Also the truck issue (blown out of all proportion by a Patton Biographer - one Ladislas Farago) - was not so much a case of 'wrong trucks' but trucks designed to run more efficiently on very coarse fuel which had become common earlier in the war MT67 and not the higher quality MT80 stuff coming out of the PLUTO Pipeline - this MT80 fuel had the unexpected effect of damaging the engines (including the replacement engines) of those 3 ton trucks as it burned hotter than the MT67 until the manufacturer could get to grips with the issue which they eventually did. An unforeseen issue probably made worse as PLUTO like MULBERRY was top secret project.
 
"Seine to Antwerp in 4 days put that idea on hold"

(Laughter) 29 August====> 1st September and THAT HAPPENED only because of Cobra and a little Franco-American turning movement further south called Dragoon. Nothing 21st Army Group originally did, actually compelled the pell mell German retreat despite the "Caen Alibi". And I do not fault the Canadians for this. Their generals actually came up with the plans that cleared the Caen shoulder.

Electrical shorts due to French rain killed those trucks, not just fuel octane rating and that problem could not be fixed., The 1104 each of 3 tonne trucks permanently lost until finally replaced (not repaied) is not a small problem. 33,000 tonnes of lift =`16 divisions/days operations per lorried lift per day. Most of the British army in France actually used that amount of lift (600 tonnes daily). Monty only estimated 400 tonnes; not 600. So losing 1/4 of your weekly lift assigned kind of hurts more.

I never mentioned Mulberry, because that screw-up was more weather related; but it, too, could have been better thought through (US Navy problem, there.). And move them? Hardly. Once sited; those quays were supposed to stay put until channel ports took up the slack.. .
 
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