During World War II the Manitowoc Shipbuilding Company built 28 submarines at Manitowoc, Wisconsin. The first 10 were Gato-class, "thin-skin" boats, with test depths of 300 feet. Initial sea trials were done in Lake Michigan. Later the submarines were sent down the Mississippi River to New Orleans for final completion and fitting out.
Founded in 1902, Manitowoc was a well-established yard with a long history of building excellent ships for Great Lakes service. By 1940 it had built 306 vessels of various types, but never a warship.
As the Navy began to develop its Fleet in the late 1930s, the yard hoped to find work building small warships up to destroyer size. But they were turned down, as contracts went to larger shipyards on the Atlantic, Pacific, and Gulf coasts. Nevertheless, top Navy officials were well aware of Manitowoc's reputation for quality work.