To follow the HTP route, some info from Norman Friedman's British Submarines in the Cold War Era.
In 1945-46 the idea was to use two Walter turbines, a 2,500bhp turbine based on captured examples and a larger 7,500/6,250bhp Type 18X based on the planned larger German turbines that were never built. These would be doubled up to give 15,000shp.
The British captured the two HTP production units at Bad Lauterberg and moved them back to the UK. It was estimated each operational submarine would require 150 tons per patrol, so a flotilla of 10 in wartime making 8 patrols each would use 12,000 tons annually - which was the output of four Bad Lauterberg units. HTP cost £120 per ton so one years fuel for ten submarines would cost £1.4M. Given the lack of alternatives that cost was accepted.
In late 1947 Barrow only had 85 tons, the MoS had promised 300-400 tons! The Walter turbine had not even left Germany at that time and the test works at Barrow hadn't been completed due to a shortage of cement and steel.
By September 1949 the cost was £250 per ton to make plus £100 per ton to store. A submarine would require £625,000 of fuel per year and the production plant would cost £2.5M to build. Special tankers were also needed (only HMS Spalbeck existed then).
When the two 'E's were approved the cost included £2.7M for fuel and storage and £1M for production plant (the two subs were estimated at £1.6M). The fuel need was 4,500 tons per year 1951-53 and 6,000 tons annually thereafter. At that time in the UK there was only 412 tons of storage with 900 tons planned at Portland (though considered unsuitable) and a further two storage sites of 1,000 tons each were wanted.
The high costs were beginning to make the Admirals baulk, they began looking at high-capacity battery subs and even oxygen. But by 1952 production costs had fallen (in fact they thought it might fall to a fifth and actually work out cheaper than high-capacity batteries). Work in 1952 shifted to HTP-fed closed-cycle diesels for economy and greater endurance and Ricardo began trials using a General Motors 1-71, Rolls-Royce then modified an ASR III diesel. They wanted to install it aboard HMS Scotsman for trials but in 1955 the Sea Lords deemed it might interfere with Vickers' work on the nuclear submarine programme and the conversion was cancelled. HTP was out, nuclear was in.
Mountbatten then quickly put it back on the agenda in 1956 married with the Albacore hull (plus on the table was the Strike Submarine - basically a modified Porpoise with Regulus II. Yet the logistics remained troublesome. HTP was £130 per ton (it was thought the Treasury would actually assess that nuclear was cheaper). It was being used in torpedoes and £14M worth was earmarked for FAA aircraft plus the RAF was had their own growing needs. Both the Albacore and Strike Submarine projects were axed in favour of concentrating on the nuclear programme.
Now for the nuclear tale.
The Admiralty Chemical Advisory Panel in 1947 notes the possibility of a nuclear-powered submarine.
By 1950 thoughts turned to a reactor using unenriched uranium with a graphite moderator and gas coolant. This was impractical as the gas circulation and graphite moderator were too weak to withstand combat shocks.
The Atomic Energy Research Establishment had enough spare resources for one project - allocated to the submarine reactor. They had in mind a high-temperature thermal reactor using enriched uranium. The Admiralty agreed and estimated R&D cost for the reactor and heat exchanger was £2M. The fuel would cost £600,000 but would give an endurance of 100 days at 25kts and be recoverable for further use in other parts of the atomic programme. In contrast HTP for 100 days use even at the widely optimistic £100 per ton would cost £12M and oxygen instead of HTP would cost £2M.
In 1950 enriched uranium stocks were forecast to be plentiful, around 1952 everything went into bombs and left the submarines nothing so the programme was halted. In March 1954 the AEA thought they might have some spare for the prototype plant. By then the US had a land prototype running, the UK asked for details but rebuffed. In June 1954 the Naval Section was formed at Harwell. By June 1955 their work allowed plans to start for a 15-20,000shp plant. At this time USS Nautilus was complete.
In February 1956 the Treasury approves the land-based prototype and the submarine. In January 1956 the prototype reactor contract was let. Vickers Nuclear Engineering Co. was formed by Vickers, Foster-Wheeler and Rolls-Royce. Dounreay was selected as the prototype site and it was hoped to be installed in 1958.
Efforts to get access to US naval reactor technology began in mid-1955, with some favourable response even from Eisenhower and in February 1956 Macmillan was told they were happy to amend the US/UK Military Co-operation Agreement to cover naval reactors once the election was over.
The EinC wanted the information but there were doubts how applicable the information would be to the Admiralty project, Friedman takes this as an indication the Harwell design at this stage was liquid metal-cooled. Plus they feared locking the reactors into US/UK secrecy would prevent commercial ship applications (seen as a big money spinner then but another chimera). Then Suez blew up the effort, not until February 1957 was the damage repaired.
By then the Admiralty seemed desperate for information on all reactors including water-cooled which Friedman suggests was a sign that the design was not going well.
In May 1957 Rickover offers a complete reactor or submarine. They were torn between accepting and throwing national effort under the bus or resisting (as they had with Terrier). The prototype submarine was put into the 1957-58 Programme at a cost of £28M, the Treasury baulked but Mountbatten got USS Nautilus to visit the UK and the future was clear once it cleaned up in Exercises 'Strikeback' and 'Rum Tub'. Then a split occurred between the submarine plant and a scaled-down Calder Hall type design for commercial ships, but this was patched up. Britain wanted a firm-to-firm deal with the US, Rickover said "no".
By late January 1958 the US was offering the Westinghouse S3W fitted to the Skate-class but the Admiralty wanted the more powerful S5W being fitted to the Skipjack-class. It was also easier to fit the S5W to Dreadnought. Rickover grudgingly agreed on the condition that further access to other US reactors was blocked. This went into the Anglo-American bilateral agreement of 1958 which also gave the weapons access. Rickover also attempted to impose a condition on officer selection but this was rejected.
Admiral Burke took this template and ran with it - in 1959 the Dutch negotiated a similar reactor deal but wanted a smaller reactor and the S5W proved too expensive, Canada was offered the Skipjack, Italy began their programme which led to the Marconi design, presumably under the same bilateral basis. Friedman says it's unclear whether France was offered a bilateral deal at this time.
Rolls-Royce and Associates was formed to build the powerplant in cooperation with Westinghouse, who built the rear hull section (from British steel) for Dreadnought. The original prototype 15,000shp plant was therefore abandoned.
The succeeding Valiant-class were in effect what Dreadnought would have been apart from having a US reactor (Core A). The planned 20,000shp production plant was to use the Dounreay core based off lessons learnt from Core A. The Admiralty Board approved the project in October 1960 but UKAEA seems to have been unwilling to fund a naval programme and it was hoped Rolls-Royce would dip into its own pockets to help. This became Core B fitted to the Swiftsure-class (this class was too soon to get the PWR2 then under development).
So the details on the 1954-58 Harwell/Admiralty effort are pretty skimpy. It may have begun as a liquid-metal cooled reactor but clearly had run into design issues by 1957 and perhaps had been changed to a PWR at that time. Dreadnought had been approved so its clear the Admiralty felt sure they would have a reactor for it - but they may have been simply reassured enough to suppose a US reactor would be available whatever happened.
If France did receive an offer in 1959 and reject it, that is understandable. Clearly there was two camps in Britain for and against getting a US reactor. They wanted the know-how but the didn't necessarily want to be locked into building a US design and giving up all commercial and industrial opportunities.
