The film does not portray a historical event. The British Royal Navy had captured the first naval Enigma machine in May 1941, before the US had entered the war. The American portrayal offended many of the British military and public. The Allies captured Enigma-related codebooks and machines about fifteen times during the War; all but two of these by British forces. The Royal Canadian Navy captured "U-744" in March 1944 and the U.S. Navy seized in June 1944. By this time, the Allies were already routinely decoding German naval Enigma traffic.