As the Civil War ramped up, the Union turned to a Frenchman for assistance. Brutus de Villeroi was an engineer with some experience building submersible vessels: in 1832 he had completed one that was nearly eleven feet long and about two feet wide and was meant to carry a crew of three. He attempted to sell it to the French navy at least three times, but was turned down on each occasion. Then the United States, concerned about the ironclad ships the Confederacy was purportedly building, came calling. The contract for the submarine that would be known as Alligator was signed on 1 November 1861; it specified a delivery date no more than forty days later. As might have been expected, that deadline came and went. It wasn’t until 180 days later, on 1 May 1862, that the vessel was launched.

The strange-looking ship that was towed to the Philadelphia Navy Yard for fitting out was 30 feet long and 6-8 feet wide and could carry a crew of more than a dozen men. In the overhead, holes were cut in the iron hull and filled with panes of glass so the men within had at least some idea of what was going on in the world above them. They breathed air that was pumped in through tubes that floated on the surface. Originally propelled by nothing more complicated than several sets of oars, Alligator was soon fitted with a hand-cranked propeller. Her exterior was painted dark green, which, in addition to her low profile and small eye-like windows, prompted a reporter to give the boat her reptilian nickname, which stuck. The Navy accepted Alligator on 13 June 1862, although she was never commissioned.

No one seemed to know quite what to do with the unusual vessel. At one point she was sent up the James River to City Point for a potential attack on the Confederate navy. But the senior Union naval officer declared that the sub was worse than useless to him: he did not have any suitable targets for her to attack and if she were captured she could be used to great effect against Union gunboats. So back to the Washington Navy Yard Alligator went. More tests were conducted—some of her maneuvers were observed by President Lincoln—but her new commanding officer soon pronounced her a failure.

In the spring of 1863 there was a glimmer of hope: Rear Admiral Samuel du Pont requested permission to use Alligator in an attack on Charleston, South Carolina. She was subsequently tethered to a surface vessel, USS SUMPTER, which then headed south. Unfortunately, the travelers ran into terrible weather off Cape Hatteras and, on 2 April, SUMPTER’s commander chose to cut the small sub, which was causing the larger vessel to wallow dangerously in the churning water, free. She was never seen again.