Gavin Merrick Long was an Australian journalist and military historian. He was the general editor of the official history series Australia in the War of 1939–1945 and the author of three of its 22 volumes.

Australia in the War of 1939–1945 is a 22-volume official history series covering Australian involvement in the Second World War. The series was published by the Australian War Memorial between 1952 and 1977, most of the volumes being edited by Gavin Long, who also wrote three volumes and the summary volume The Six Year War.