The Royal Australian Air Force was founded in 1921 and by the Second World War was well established. The RAAF sent pilots to Great Britain in 1939 to help support the RAF during the early days of the war, with up to 32 pilots fighting in that conflict. In photographs it is very easy to identify Australian personnel alongside their RAF brethren because of the much darker shade of blue adopted by the RAAF. This was a deep midnight blue colour as seen in this World War II era field service cap:

The cap is made of fine wool, with a black rayon type lining:

The front of the cap has a pair of black plastic buttons with a crowned eagle:

The interior of the cap has a white printed label with sizing, a date of 1943 and a factory code of ‘Q83’:

The caps were worn by air and ground crew with over 10,000 Australians serving in Bomber Command in Europe as well as squadrons in the Far East. This photograph shows the aircrew of 458 Squadron at RAAF Holme on Spalding Moor, with the Australian members of the squadron clearly visible in their darker uniforms, with the man on the left wearing the FS cap: