The Self Defense Test Ship (SDTS) is one of the assets of the US Navy. It is a refurbished ship, operated by remote control, which is designed to support self-defense engineering, testing, and evaluation. Being unmanned, it avoids the safety constraints and other problems associated with manned ships. During typical operations, launched threats attack the ship and the combat or weapon system being tested responds to these threats, defending the ship. The prearranged attack is in practice aimed at a decoy barge pulled 150 feet behind the SDTS in case of damage.

The current SDTS is the former , which replaced the former in 2005.