Beginning in December 1896, the Crescent Shipyard, under Nixon's oversight, built the United States' first submarines. The was one of the creations of that shipyard and is a very significant achievement in naval technology. The submarine's success led to an order for more submarines of the "Holland Type" by the Navy. Those subs, known as the s, were built at the Crescent Shipyard and the Union Iron Works, a shipbuilding firm located near Mare Island Naval Shipyard, 20 miles north of San Francisco. These submarines became America's first fleet of underwater fighting vessels, and were operated by the United States Navy on both coasts.