The ATS had its roots in the Women's Auxiliary Army Corps (WAAC), which formed in 1917 as a voluntary service. During the First World War its members served in a number of jobs including clerks, cooks, telephonists and waitresses. The WAAC was disbanded after four years in 1921.
Prior to the Second World War, the government decided to establish a new Corps for women, and an advisory council, which included members of the Territorial Army (TA), the Women's Transport Service and the Women's Legion, was set up. The council decided that the ATS would be attached to the Territorial Army, and the women serving would receive two thirds the pay of male soldiers.
All women in the Army joined the ATS except for nurses, who joined Queen Alexandra's Imperial Military Nursing Service (QAIMS), and medical and dental officers, who were commissioned directly into the Army and held Army ranks.
As more men joined the war effort, it was decided to increase the size of the ATS, with numbers reaching 65,000 by September 1941. Women between the ages of 17 and 43 were allowed to join, although these rules were relaxed in order to allow WAAC veterans to join up to the age of 50. The duties of members were also expanded, seeing ATS orderlies, drivers, postal workers and ammunition inspectors.
Other options under the Act included joining the Women's Voluntary Service (WVS), which supplemented the emergency services at home, or the Women's Land Army, helping on farms.
There was also provision made in the Act for objection to service on moral grounds, as about a third of those on the conscientious objectors list were women. A number of women were prosecuted as a result of the Act, some even being imprisoned. Despite this, by 1943 about 9 out of 10 women were taking an active part in the war effort.
Women were barred from serving in battle, but due to shortages of men, ATS members, as well as members of the other women's voluntary services, took over many support tasks, such as radar operators, forming part of the crews of anti-aircraft guns and military police. By VE Day, there were over 190,000 members of the Women's Auxiliary Territorial Service.
Famous members of the ATS included Princess (later Queen) Elizabeth, eldest daughter of the King, and Mary Churchill, youngest daughter of the Prime Minister.
| Auxiliary Territorial Service rank | Equivalent Army rank |
| Volunteer | Private |
| Chief Volunteer | Lance-Corporal |
| Sub-Leader | Corporal |
| Section Leader | Sergeant |
| Senior Leader | Warrant Officer Class II |
| Company Assistant | Second Lieutenant |
| Junior Commander | Lieutenant |
| Company Commander | Captain |
| Senior Commandant | Major |
| Chief Commandant | Lieutenant-Colonel |
| Controller | Colonel |
| Senior Controller | Brigadier |
| Chief Controller | Major-General |
On 9 May 1941, the ATS rank structure was reorganized, as from July 1941 the ATS was given full military status and members were no longer volunteers. Other Ranks now held identical ranks to male Army personnel, but officers continued to have a separate rank system.
| Auxiliary Territorial Service rank | Equivalent Army rank |
| Second Subaltern | Second Lieutenant |
| Subaltern | Lieutenant |
| Junior Commander | Captain |
| Senior Commander | Major |
| Chief Commander | Lieutenant-Colonel |
| Controller | Colonel |
| Senior Controller | Brigadier |
| Chief Controller | Major-General |
The uniforms and badges of rank remained the same, although crowns replaced laurel wreaths in the rank insignia. ATS members were now required to salute all senior officers.