Small submarines definitely still exist today, though to my knowledge the operator sits inside. I’m not aware of a current design which requires lying on one’s stomach and pedaling.

Although the pictured invention might look a bit silly to a modern day viewer, the idea behind the invention still has merit to it:

“The only way by which to make the action of the torpedo actually certain was to put an experienced operator inside it; for, while its automatic machinery operates with almost human intelligence, there is no certainty that it will on long ranges do exactly what is required of it.”

One-Man Submarine Invention of an American: Tiny Torpedo Boat, Said to be Used by German Raider, Was Anticipated by the Ingenious Craft of Thomas J. Moriarty

From Sunday, January 28, 1917