Goofs

In the opening scenes U47 is shown sailing on a calm sea, which then cuts to a heavy swell, then back to a calm sea.

At 12.00 and 1.17, a radio is turned on and immediately begins playing music. These would have been valve radios and would have needed time to warm up before they produced any sound.

When U47 surfaces it is fired upon by 3 destroyers, multiple times, but is not hit once. This would not have been likely.