When Mallory and Barnsby return to the Chetnik camp to free their comrades Mallory addresses Schroeder's clerk as Sergeant. The clerk is wearing corporal's chevrons. Sergeants in the German army in WWII wore their rank insignia on their shoulder tabs.
Continuity with "The Guns of Navarone": Mallory and Miller are shown at the beginning of this film being picked up by the Royal Navy ships passing Navarone. In that scene, they are wearing German uniform jackets. They discarded those jackets while they were in the gun cave at the end of "The Guns of Navarone".