Early submarine experiments were an international phenomenon

Did countries besides the United States experiment with early submarines around the American Revolution?

Yes. France, Britain, and others showed interest, although it is often unclear whether particular projects represented governments or private inventors.

France, Britain, and other countries all showed interest in underwater craft during the era of the American Revolution. The surviving record often makes it hard to distinguish official state programs from privately driven invention. A later exchange mentions an English craft associated with Charles II and a trip on the Thames, but its classification as a submarine remains uncertain. A vessel able to submerge and return is still different from a fully developed submarine, so these scattered experiments are better treated as submersibles than as early national submarine services.