Women served in the WRNS during the First World War and a good number were based at HMS Hornet in Gosport, which became the home base of the Thornycroft-designed Coastal Motor Boats. Formed in 1917, there were around 5,500 by the end of the war. A further 3,000, who had been part of the Royal Naval Air Service, chose to transfer to the newly formed Royal Air Force.

The branch was disbanded in 1920 and then revived in 1939 as the Second World War loomed. The were signallers, cooks, clerks, radar plotters, weapons analysts, electricians, ordnance engineers, vehicle drivers and flew air transport planes. Famously they worked at Bletchley Park codebreaking the German Enigma cypher machines. By the end of the war there were 75000 active servicewomen.

Around 3000 worked with Coastal Forces.