X1 and the awkward logic of cruiser submarines

X1 and the M class reflected the cruiser-submarine idea: a large submarine sent to find and attack merchant shipping. The Royal Navy's overseas bases and surface cruisers made that mission redundant in most theatres. In the Mediterranean, large submarines were ill-suited to a confined, air-threatened sea, helping explain the later emphasis on smaller U-class boats with the 10th Submarine Flotilla at Malta. The South and East China Seas were the exceptional case where distance and air power gave a submerged raider a stronger rationale. X1 remained an unconvincing answer even there. Its diving procedures and resistance to water ingress made it the less hazardous choice than Surcouf, though neither large submarine is presented as desirable.