After the war she was converted back into a passenger liner and renamed Warwick Castle.

Harland and Wolff built Pretoria Castle in Belfast, launching her in 1938 and completing her in April 1939.

In July 1942 the Admiralty bought her outright for conversion to an escort carrier by Swan Hunter on Tyneside.

In 1945 she twice became part of aviation history, firstly when British test pilot Captain Eric "Winkle" Brown landed a Bell Airacobra Mk.

1 on her flight deck - the first carrier landing made using an aircraft with a tricycle undercarriage, when Brown declared an emergency and was given permission to make a deck landing; a ruse which had previously been agreed with the carrier's captain, Caspar John, during initial trials for rubber deck landings planned for future carriers, and then by hosting the first ever landings and take-offs by a glider, performed by John Sproule in a Slingsby T.20 as part of research into "round-down" turbulence.