Number 209 Squadron of the British Royal Air Force was originally formed from a nucleus of "Naval Eight" on 1 February 1917 at Saint-Pol-sur-Mer, France, as No.

[9] The number, badge and motto is in service within the RAF Air Cadets at 209 (West Bridgford) Squadron ATC in Nottinghamshire.

During the remainder of World War I, 209 Squadron flew Sopwith Camels over the Western Front on fighter and ground support missions.

[9] Familiarisation with the U.S. supplied Catalinas was aided by the secondment of U.S. military personnel who also flew on active service patrols, despite the U.S. being a neutral power at the time.

Anti-submarine patrols were flown over the Atlantic from RAF Castle Archdale on Lough Erne, in Northern Ireland, using the Donegal Corridor over neutral Eire.

It flew patrols over the Indian Ocean with detached bases in South Africa, Madagascar, Oman and the Seychelles to extend its cover.

In July 1945 the squadron moved to Ceylon (now Sri Lanka), with recently acquired Short Sunderland MkVs, with a detachment at Rangoon (now Yangon), to harass Japanese shipping along the coast from Burma (now Myanmar) to Malaya.