She joined the Women's Auxiliary Territorial Service, as No. 230873 Second Subaltern Elizabeth Windsor. She trained as a driver and mechanic, drove a military truck, and rose to the rank of Junior Commander.[22] She is, at present, "the only living head of state who served in uniform during World War II".
http://en.wikipedia.org/wiki/Elizabeth_II_of_the_United_Kingdom
I see that. Thank you !