Castle Wolfenstein (1981)

Castle Wolfenstein is a slow-paced stealth game set in World War II. The game's main objective is to traverse the levels of the castle to find the secret war plans and escape alive. Progressively higher military ranks are earned upon each successful escape with the war plans, and the game becomes correspondingly more difficult as each higher rank is achieved. There are 8 ranks, beginning with Private, culminating at the rank of Field Marshall.