Terry Pratchett's Monstrous Regiment

Polly has to become a boy in a hurry. Cutting off her hair and wearing trousers is easy. Learning to fart and belch in public will take more time. And now she's enlisted in the army. But there's a war on. There's always a war on. And Polly and her fellow recruits are suddenly in the thick of it without any training and the enemy is hunting them. And as they take the war to the heart of the enemy, they have to use all the resources of the Monstrous Regiment. Adapted by Stephen Briggs.