Monstrous Regiment by Terry Pratchett was originally published in 2003. It fits into the Fantasy genre and is recommended for adult readers.
Monstrous Regiment was a great disappointment to me. The particular volume I read was covered with reviews that listed of how funny it was and while there were one or two funny lines that I shared with my husband overall it wasn’t anything to rave about. The plot was interesting enough. It takes place in the country of Borogravia that takes part in wars continuously with all of the surrounding countries. Polly Perks decided to join the army disguised as a man to find her brother that joined up a year before and went missing. Polly, also known as Oscar, found that it was harder than she thought to appear male and was soon discovered my a mysterious someone who instructed her to put a pair of socks in her pants to “bulge where she should”. Polly/Oscar finds out later that she is not alone in her secret and that everyone in the army has something to hide whether it’s a secret like hers or something else. Polly and her fellow “men” find out what they are made of and are surprised at what they can accomplish in the end. Overall it wasn’t great. I wouldn’t recommend it to anyone but at the same time I don’t think I’d tell people not to read it because it wasn’t bad either it just didn’t wow me.