 Commander Fraser (Mills) is determined to prove that attack by human torpedoes is practical, despite scepticism from RN higher echelons.Fraser assembles and trains a force of British commando frogmen officers and ratings to use the Mk I Human Torpedo manned torpedoes (Chariots) at their Scottish base.After being refused permission to attack "Tirpitz", due to the RN policy of avoiding unproven weaponry, the team manage to attach dummy limpet mines to the admiral's own ship.