The Sovereign is the nominal Commander-in-Chief of the Armed forces in Great Britain, but operationally and managerially, none of the very topmost staff officers is female as far as I know. This may well change though as the number of women commissioned officers in the British Army, Royal Air Force and Royal Navy increases.
As it happens the Queen did serve in WW2, when she was Princess Elizabeth; in one of the women's auxiliary (non-combatant) units. Among other things she learnt in that service, was how to drive and carry out basic vehicle maintenance.
