Per the WWRW report this week, the Chinese have made a sailless submarine prototype. This is not a new idea; the United States, the Soviet Union, and France have kicked this idea around in the past. Let’s look into why one might want to delete the sail, and what tradeoffs that brings.
Why would one want to delete a sail? That’s simple: speed. US Navy sub designers reckoned that deleting the sail (and the drag from it) would gain you about 1.5 knots of speed, all other things being equal. It also removes the problem of inducing a snap roll tendency in turns.
Like everything else, it’s not without its tradeoffs. Clearly, we still need masts and some way for the crew to enter and leave the submarine. We also are going to need some sort of conning tower facility to steer the sub when it’s surfaced. Prior designs tend to accomplish the first by folding masts and periscopes down into a fairing, and having a retractable conning tower for steering and crew access, retracting again into a fairing. That fairing will add some drag back. Bureau of Ships actually figured that a fairing capable of handling all of the relevant systems would be about as draggy as a well-designed, small sail.
Having a sail allows the submarine to be a bit deeper at periscope depth, which helps with stability in rougher sea states. The sail itself is also an aid to stability, and means that the rear fins don’t have to be as large.
The US Navy actually gave serious consideration to the sailless concept twice, going as far as to make some models of the concept when designing what would become the Los Angeles-class. However, this ran into opposition from Hyman Rickover, who wanted fast submarines now, and did not want to do a bunch of hullform comparisons when he could simply design aroudn a larger reactor and call it a day. Rickover managed to kill the concept, and the Los Angeles boats all had a traditional (albeit small) sail.