Based on

Movies like Cadets (1941)

The year is 1760: it is the time of the Seven Years' War and the advancing Russian army has taken captive 100 underage Prussian cadets. The kids are mishandled by the raping and pillaging Russians, but with the help of a Rittmeister now in the service of the Tsar, they succeed in getting away. They hole up in a deserted fort and eventually sally forward to take back their military academy from the bloodthirsty, pillaging Cossacks.