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 Squadron Royal Naval Air Service (RNAS) and saw active service in both World Wars, the Korean War and in Malaya. The use of the squadron number ceased in 1968 and it has not been reused since by an RAF squadron. However the number, badge and motto is in current service within the RAF Air Cadets at 209 Squadron ATC in Nottinghamshire.

Clairmarais aerodrome, at Clairmarais, Pas-de-Calais, France, near St. Omer and not far from Ypres, was an airfield used by the Royal Flying Corps (RFC) and later Royal Air Force (RAF) in the First World War. The site was briefly reused by the Germans during the occupation of France in the Second World War.