A hospital ship is a ship designated for primary function as a floating medical treatment facility or hospital. Most are operated by the military forces (mostly navies) of various countries, as they are intended to be used in or near war zones.
Attacking a hospital ship is a war crime. However, belligerent navies are entitled the right to board such ships for inspections.
USNS Comfort (T-AH-20) is the third United States Navy ship to bear the name Comfort, and the second Mercy-class hospital ship to join the navy fleet. The USNS prefix identifies the Comfort as a non-commissioned ship owned by the U.S. Navy and crewed by civilians from the Military Sealift Command (MSC). In accordance with the Geneva Conventions, USNS Comfort and her crew do not carry any offensive weapons. Firing upon the Comfort would be considered a war crime as the ship only carries weapons for self-defense.
Like her sister ship USNS Mercy, Comfort was built as a San Clemente Class oil tanker in 1976 by the National Steel and Shipbuilding Company. Her original name was SS Rose City and she was launched from San Diego, California.
Her career as an oil tanker ended when she was delivered to the Navy on December 1, 1987. Now, as a hospital ship, Comfort's new duties include providing emergency, on-site care for U.S. combatant forces deployed in war or other operations. Operated by the Military Sealift Command, Comfort provides rapid, flexible, and mobile medical and surgical services to support Marine Corps Air/Ground Task Forces deployed ashore, Army and Air Force units deployed ashore, and naval amphibious task forces and battle forces afloat. Secondarily, she provides mobile surgical hospital service for use by appropriate U.S. government agencies in disaster or humanitarian relief or limited humanitarian care incident to these missions or peacetime military operations. Comfort is more advanced than a field hospital but less capable than a traditional hospital on land.