Macnee studied acting at the Webber Douglas Academy of Dramatic Art, but shortly before he was to perform in his first West End leading role, which would have had him acting alongside Vivien Leigh, he was called up for the Royal Navy. He joined as an ordinary seaman in October 1942 and was commissioned a sub-lieutenant in June 1943, becoming a navigator on Motor Torpedo Boats in the English Channel and North Sea. Reassigned as first lieutenant on a second MTB, Macnee caught bronchitis just before D-Day; while he was recuperating in hospital, his boat and crew were lost in action. Two of the crew received the Distinguished Service Medal. He left the Navy in 1946 as a lieutenant.