The Washington Naval Treaty allowed France to pursue Surcouf, but treaty permission did not resolve the cruiser submarine's operational problems. The design combined underwater concealment with cruiser guns, yet its stated speeds of 10 knots submerged and 18.5 knots on the surface left it vulnerable to destroyers. A proposed elevating platform would have placed lookouts 15 meters high, but it conflicted with submarine operation and was abandoned. Surcouf was intended to be the first of three boats, leaving two unbuilt. A conventional cruiser and a separate submarine were probably a more useful purchase for the same money, especially because the Washington treaty did not limit the number of cruisers France could build.
Notable Point · 1:19:19-1:25:21
A treaty-legal cruiser submarine still had to justify its cost
The Washington Naval Treaty's allowance for Surcouf did not make the hybrid concept a better investment than separate cruisers and submarines.