Hospital ships have two missions. First, to provide a mobile, flexible, rapidly responsive afloat medical capability to provide acute medical and surgical care in support of amphibious task forces, Marine Corps, Army, and Air Force elements, forward deployed Navy elements of the fleet and fleet activities located in areas where hostilities may be imminent. Secondly, to provide a full-service hospital asset for use by other government agencies involved in the support of disaster relief and humanitarian operations worldwide. The HSS mission in joint operations is to minimize the effects of wounds, injuries, and disease on unit effectiveness, readiness, and morale.
Hospital ships have inpatient capabilities comparable to major medical facilities ashore.
Both vessels have a helicopter deck capable of landing large military helicopters, as well as side ports to take on patients at sea. Both hospital ships are converted San Clemente-class super tankers. Mercy was delivered in 1986 and Comfort in 1987. In 1996 the requirements for USNS Mercy were realigned to NMC San Diego, consistent with the BRAC closure of Naval Hospital Oakland. The location and sourcing for USNS Comfort remained under close study.