Having failed with torpedoes, John Mills and his rookie crew set out in midget submarines to try to sink the German battleship Tirpitz in this rather disappointing Second World War action adventure. Riddled with stiff-upper-lipped stereotypes, this is one of those proud re-creations of an "against the odds" mission that were the staple of postwar British cinema. However, by opting to examine the cramped conditions of his characters rather than go overboard on their heroic exploits, director Ralph Thomas struggles with the pace of the picture, and even the attack on Trondheim harbour is less than nail-biting.

In World War II, the greatest threat to the British navy is the German battleship Tirpitz. While anchored in a Norwegian fjord, it is impossible to attack by conventional means, so a plan is hatched for a special commando unit to attack it, using midget submarines to plant underwater explosives.