Goofs

At the battle with the tanks, when the Russians storm the German infantry, you can see a closeup of the same German soldier dying twice within a few seconds. His helmet is pushed into his eyes, his throat is squirting blood and he is falling towards the right edge of the screen.

In the hospital after the initial bombardment, a surgeon operates on a patient and gets blood sprayed on his cap, face and glasses. In the next shots German soldiers clear the room and there is little or no blood on those.

When the Stukas bomb the fortress we can see them releasing their bombs at a very low altitude, at 50 meters for the best. This is impossible: the minimal altitude of releasing a bomb was 450-500 meters, and the pilot couldn't even pull the bomber up from this low. Also the bombs would be visible for the eye as they are not falling faster than the plane that released them, but we see nothing, just an explosion on the ground.

During all the fighting the Russian soldiers never put on their helmets.

During the dogfight scene when the two Messerschmitts shoot down the Soviet I-16, the Soviet fighter passes over the yard at a very low altitude. While it's actually possible, it's pretty much a suicide maneuver because the plane would lose speed and maneuverability when pulling up, practically becoming a sitting duck for the one in pursuit. It's especially dangerous for this particular dogfight as the Bf-109 had a great advantage in speed and especially vertical climbing over the I-16, so the Soviet pilot is definitely giving up any chances. Also, the Soviet plane looks way too small while passing by the buildings.

In the beginning, you can see a partially destroyed building with some of it's facade gone and it appears that the walls are made of particle board. No outer walls are made from it and particle board wasn't really used until the late 40's and then mostly in furniture. The building is clearly a hastily made movie prop and not a real house.

Around time code 1h20, we see Stukas bombing the fortress. The firsts Stukas pass arrive correctly. The other Stukas have their head down and arrive on the back. Technicians have probably inverted the images.

When Sasha/Sashka finds Anya hiding in the wrecked store, a German soldier with a light machine gun enters and Sasha shoots him with his pistol. The German is wearing short, laced ankle boots and British-style canvas anklets. These low boots were issued only to rear-area troops from mid-1940, not to front-line soldiers who continued to wear high marching boots until 1943.

When Comissar Fomin is saving the people from the hospital on the bridge, and the civilians are standing up, walking slowly towards the fortress, you can see the muzzle flash of the German machine gun just a few steps behind them, in the lower left part of the screen, but no sound. At this point all the Germans were supposedly dead, including the gunners, but probably the extras messed up their role.