If you're looking for manga similar to Girls und Panzer: Little Army, you might like these titles.
Living by the sea, protecting the sea, and journeying across the sea...They're the Blue Mermaids! Because of a shift in tectonic plates around 100 years ago, Japan lost much of its area to submergence. To preserve Japan's territories, Coastal Cities sprung up, one after the other. Eventually, they became Marine Cities, and along with the expansion of sea-lanes to connect them, the need arose for a sizable staff to protect the seas. At the same time, maritime jobs were becoming more popular among women. Hence, the Blue Mermaids, tasked with keeping the seas safe, had become every female student's dream job. This is when childhood friends Akeno Misaki and Moeka China enroll in a marine high school in Yokosuka, along with other girls who share their goal of "Becoming a Blue Mermaid."
Yosora Fujimitsu is a newly admitted student to North Gate National Military Academy, a school where the elite gather. Yosora possesses both beauty and intelligence, but he immediately feels uneasy at his new school. He thinks, "At this school, there's some kind of big secret." A vortex of speculations occupies Yosora as he's led toward that secret.
Glory won over the roar of cannon fire, peace exists simply as a time to prepare for the next battle. A soldier in a militarily-advanced nation, Balzer quickly advanced in rank. However, his career takes a sudden turn when he is reassigned as an adviser at a military school in a neighboring allied nation. Faced with little military power, untrained students, and civilian opposition to firearms, will Major Balzer be able to win over the soldiers and civilians?