GAO reviewed the Navy’s MK-48 Advanced Capability (ADCAP) torpedo propulsion system upgrade program, focusing on whether the: (1) Navy needs an upgraded propulsion system; (2) upgrade would meet Navy noise reduction requirements; and (3) Navy is conducting research in alternative noise reduction technology. GAO found that: (1) the current system would meet the Navy’s requirements for the SSN-21 Seawolf submarine; (2) the Seawolf will have a very limited production run; (3) the Navy is continuing the development of the upgrade and will make it available to submarines that can fire MK-48 ADCAP torpedoes, although they operate at higher noise levels than the Seawolf, which limits the value of the quieter system; (4) the upgrade was not intended to meet and will not lead to meeting the Navy’s 1986 noise reduction requirements; (5) the Navy has basic and exploratory research programs in alternative noise reduction technologies; and (6) cancelling the upgrade and continuing the other research would be in line with the Department of Defense’s (DOD) revised weapons acquisition strategy.