premise: Brutus de Villeroi (1794–1874) was a French engineer of the 19th century, born Brutus Amédée Villeroi (he added the aristocratic "de" in his later years) in the city of Tours and soon moved to Nantes, who developed some of the first operational submarines, and the first submarine of the United States Navy, the Alligator in 1862.
hypothesis: The United States Navy only had one operational submarine in 1863. It was called the Alligator.
reason: We don't know if they had any other subs by 1863.