Laid down as the refrigerated cargo ship Telemachus for the Alfred Holt Line, but taken over by the Admiralty in February 1941, for conversion to an escort carrier, HMS Activity was commissioned on 29 September 1942. Until August 1944, she escorted convoys, where her aircraft participated in the sinking of two U-boats and damaged three others.
HMS Activity was then transferred to the Eastern fleet as an aircraft and personnel transport. After the war she was converted back for civilian use and renamed Breconshire for the Glen Line. She operated until 1967 when she was scrapped.