Auxiliary Territorial Service
The Auxiliary Territorial Service (ATS; often pronounced as an acronym) was the women's branch of the British Army during the Second World War. It was formed on 9 September 1938, initially as a women's voluntary service, and existed until 1 February 1949, when it was merged into the Women's Royal Army Corps.
Source: Wikipedia — Auxiliary Territorial Service (CC BY-SA 4.0)