Nejimaki Seirei Senki: Tenkyou no Alderamin

The Katjvarna Empire and the Kioka Republic are at war, and Katjvarna is currently defending their border against Kioka's attacks. Yatorishino is from an influential family in the empire, and she's taking the high ranking officer exams. To make sure she passes at the top, she's convinced lazy, anti-war, girl-crazy Ikuta to take the exams as well and help her, in exchange for a favor from her family. The first, written test goes as planned, and then they head off on a boat for the next. Unfortunately, the boat sinks, and Yatorishino, Ikuta, some other examinees, and a mysterious, important little girl are stranded behind enemy lines!

(Source: MangaHelpers)