sw: BSAAC, very wet routes, was happy to contemplate a mixed fleet, land and marine (Princess/Tudor/Comet 1, no doubt BOAC's Medium Range Empire to be Britannia). BOAC did not exit marine until 1950. US had Mars, France, Late.631. The received wisdom dismissal of commercial marine, as destroyed by wartime concrete, is, I suggest, trite. It was operating economics: DC-4/L-049 were game-changing, even before DC-6/L-1049. For MR, Neptune delivered loiter/endurance matching any marine type, but readily maintainable. Did any ASW concept ever involve wallowing silently on deep-ocean swell?
MoS probably continued to fund Saro MR "study", 1952-55, simply to sustain a team-in-being while resolving whether RAF would take up their rocket-interceptor schemes. That is also why Saro in 1951/2 was given the fabrication of Valiant nose and Viscount wing: any production run for a big-Saro would have been beyond Cowes' capacity and was to be joint with Vickers-Armstrongs.