Tank commander Sergeant Tessen does not believe that his crew can become a successful collective and requests his transfer, but he finally withdraws his request due to a young boy to whom he carelessly promised a tank model. However, this would first have to be made by the crew members. New difficulties arise, even though everyone agrees to keep the soldier's word of honor. The spell is only broken when the tank gets into a dangerous situation during an underwater journey and the four of them have to prove themselves together.