During the 1941 Italian manned torpedo
raid on Alexandria, two British battleships, and , are severely damaged. The British are worried that this new tactic will afford the Italians naval supremacy in the
Mediterranean and the ability to strike their primary target, the Royal Navy base at
Gibraltar. To counter this threat, bomb-disposal expert Lionel Crabb is posted to Gibraltar. He organises a small team of divers to intercept the Italian attacks and defuse the bombs. Meanwhile, from
Algeciras in neutral
Spain, Italian expert on underwater operations Antonio Tomolino is secretly watching the British base in Gibraltar and planning new attacks. After the Italians mount a failed attack upon a cruiser in Gibraltar, Crabb and his divers recover one of the manned torpedoes and begin to repair it.
Chief Petty Officer Thorpe takes command of physical and diving training. After a further series of attacks against ships in Gibraltar harbour and an attempt to recover secret documents from a wrecked aircraft, Crabb visits
Algeciras to discover the Italians' base of operations. After following a man with an Italian
tattoo to the interned Italian ship the
Olterra, he discovers that the ship's hold is being used as a workshop and base for the operations. The ship's underwater door is used for the manned torpedoes and by frogmen, which leaves them undiscovered by Spanish authorities. Crabb reports the discovery of the
Olterra to his superiors, but under the laws of neutrality, he cannot arrange an attack without top-level authority. Meanwhile, the Italians plan a major attack on a British convoy. Crabb ignores orders and, with the manned torpedo repaired, he and another diver infiltrate the docks at Algeciras, launching a preemptive strike on the
Olterra that destroys the ship, workshop and crew. The next morning, with the convoy leaving Gibraltar, Thorpe informs Crabb that for his bravery in this operation he has been awarded the
George Medal, commenting to his men: "You all deserve a ruddy medal!" ==Cast==