Sea Shadow was built in 1985 and used in secret but normal service until her public debut in 1993, to examine the application of stealth technology on naval vessels. In addition, the ship was designed to test the use of automation to enable the reduction of crew size. The ship was created by the Defense Advanced Research Projects Agency (DARPA), the U.S. Navy and Lockheed. Sea Shadow was developed at Lockheed’s Redwood City, California facility, inside the Hughes Mining Barge, which functioned as a floating drydock during construction and testing.
Sea Shadow has a SWATH hull design. Below the water are submerged twin hulls, each with a propeller, aft stabilizer, and inboard hydrofoil. The portion of the ship above water is connected to the hulls via the two angled struts. The SWATH design helps the ship remain stable even in very rough water of up to sea state 6 (wave height of 18 feet (5.5 m) or “very rough” sea).