5. The British Auxiliary Territorial Service (ATS)
During World War II, thousands of British women joined the Auxiliary Territorial Service (ATS), serving in roles such as anti-aircraft gunners, drivers, and mechanics. Notably, Princess Elizabeth (later Queen Elizabeth II) enlisted, training as a driver and mechanic, and reaching the rank of Junior Commander. Their contributions were vital to wartime Britain, often operating under fire. More at Imperial War Museums.