By December 1939, 43,000 women had volunteered for active duty in the Women's Auxiliary Services of the Army, Navy and Air Force. They were not allowed to fight but did work that supported the efforts of the soldiers, sailors and airmen. At first this included typing, cooking, cleaning, driving and operating telephone switchboards but they were soon given more military work to do, such as identifying enemy aircraft, plotting air and shipping movements on battle maps, and acting as motorcycle messengers.

The government wanted women to join up so they could take the places of men who could then be sent off to fight. As a result, in 1941 they introduced conscription for all single women aged between 20 and 30. Women had to choose whether they wanted to join the armed forces or work in vital industries. Early in 1942, women aged 19 were also called up. By January 1942, over 213,000 were serving in the Auxiliary Services. The number of women entering the services fell slightly in 1943 as more people were needed to work in aircraft production but by June 1944 over 450,000 women were serving in the armed forces (the equivalent number of men was 4 ½ million).

As the war went on, women were given more dangerous work to do, such as crewing anti-aircraft guns and searchlights. Women also undertook top-secret work using radar or code-breaking enemy messages. Indeed, most of the 5,000 people working at Bletchley Park using early computers and captured enemy encoding machines to read German and Japanese messages were women.