GAO reviewed the Navy’s plans to upgrade both the propulsion and the guidance and control systems of the MK-48 Advanced Capability torpedo (ADCAP), focusing on the: (1) need for the propulsion system upgrade; and (2) appropriateness of approving low-rate initial production of the guidance and control system. GAO found that: (1) the Navy believes the $249-million ADCAP propulsion system upgrade will reduce the launching submarine’s vulnerability in shallow water; (2) the propulsion upgrade will not improve ADCAP performance or reduce the submarine’s vulnerability to enemy attack because of the short ranges at which submarines are likely to be detected in shallow water; (3) the upgrade is not needed, since ADCAP is already rated operationally effective in shallow water; (4) the Navy did not establish a requirement to improve the propulsion system for use in open-ocean, deep water; and (5) low-rate initial production of the guidance and control system should not be approved until new software is developed and installed in mid-1998.