The Lovely Sergeant.
by Alan Burgess. London: Heinemann,1963.
This copy is Reader’s Book Club, 1964.
It feels like cheating, because the title is deliberate, not inadvertent. The sergeant in question was an extraordinary English woman who joined the Serbian army in 1914 (as you do), and, yes, won a commission.
It probably deserves better treatment than this, but, meh.