""She was enlisted as 230873 Second Subaltern Elizabeth Alexandra Mary Windsor in the Auxiliary Territorial Service, the ATS, [March, 1945] and sent to train as a transport officer at Camberley. The course was three weeks and Princess Elizabeth did not associate too closely with her fellow trainees.
She lunched in the officers' mess and slept the night at Windsor; 50 years later, her grandsons would eat cadet food, iron their own uniforms, polish their own boots and be shouted at on the drill square.
Despite her kid-glove treatment, Princess Elizabeth greatly appreciated her spell in the ATS, believing it gave her a confidence she had previously lacked
The war in Europe was now drawing to a close and on May 8, 1945, the two princesses were allowed out of the Palace with their Guards officer friends to mingle with the crowds in the Mall and join in the shouts of "We want the King""
Publicity stunt? Probably. I'll bet that she was the one who thought it up. Still, changing truck tires in the 40’s? Yuck.