Read Gunka No Baltzar manga
From: Easy Going Scans 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?