If Turtle had succeeded

What if Turtle's attack had succeeded during the American Revolutionary War?

It could have accelerated competing submarine programs and begun a much earlier underwater arms race.

The counterfactual begins with an American effort to scale the successful one-man Turtle into two-person and then larger craft. Britain would respond with its own designs, producing an Anglo-American underwater arms race generations before the historical submarine competition. The unusual rounded hull might persist for a time before builders adopted the easier cylindrical form. Because a sphere can withstand deep-water pressure well, the experiment could still influence diving performance even if it eventually proved awkward to steer. An eighteenth-century operational success would therefore change both the pace and the physical starting point of submarine development before the First World War.