No. 203 Squadron RAF was originally formed as No. 3 Squadron Royal Naval Air Service. It was renumbered No. 203 when the Royal Air Force was formed on 1 April 1918.

Raymond Collishaw, was a distinguished Canadian fighter pilot, squadron leader, and commanding officer who served in the Royal Naval Air Service (RNAS) and later the Royal Air Force. He was the highest scoring RNAS flying ace and the second highest scoring Canadian pilot of the First World War. He was noted as a great leader in the air, leading many of his own formations into battle. After the Great War, he became a permanent commissioned officer in the Royal Air Force (RAF), seeing action against the Bolsheviks in 1919–20, and subsequently commanding various Air Service detachments. During the Second World War, he commanded No. 204 Group in North Africa, achieving great success against the numerically and technologically superior Italian Air Force. He was retired in 1943.