The sub machine guns have wooden stock so are definitely not Stirlings which have curved magazines also. They look more like MP28 Schmiessers (not to be confused with the falsely named MP38/40) or Erma EMP35 which would have been in second line naval service at the time. (They may have been Austrian/Swiss Steyr-Solthuthurn MP34/S1-100 or even British Lanchester MK1 which were used by the RN in the war.)
When the captured Brits are being "escorted" down the gangway of the Tirpitz, the German sailors are prodding them, not with German weapons, but with British Sterling sub machine guns.
Considering the time of day In the fjord, the underwater scenes should have been pitch black.
After escaping by swimming from their sub being crushed, the British sailors are surprisingly dry when they are escorted onto the Tirpitz.
When the German patrol boat stops along side the Ingebord, the diver working on the mini-sub should have heard it and known to have stayed hidden.
The 100' Submarine Escape Training Tank in the early scenes wasn't built until 1954. Prior to this, it was a 15' tank.
The sailors and marines on the Tirpitz are wearing incorrect steel helmets. The ones that they are wearing are of World War I-type pattern, they are larger with vent studs sticking out.
When this movie was made in 1954, Queen Elizabeth II was on the throne, but throughout the war, it was her father, King George VI, who was the monarch. Whether by design or chance, most of the cast have historically accurate cap badges, which is to say they include a King's crown. The notable exception is Sir John Mills, whose cap badge has a Queen's crown.