A merchant aircraft carrier (also known as a MAC ship, the Admiralty's official 'short name')[1] was a limited-purpose aircraft carrier operated under British and Dutch civilian registry during World War II. MAC ships were adapted by adding a flight deck to a bulk grain ship or oil tanker enabling it to operate anti-submarine aircraft in support of Allied convoys during the Battle of the Atlantic.
Despite their quasi-military function, MAC ships retained their mercantile status, continued to carry cargo and operated under civilian command. MAC ships entered service from May 1943 when they began to supplement and supplant escort carriers, and remained operational until the end of the war in Europe.