A naval officer, John Mills, attempts to persuade an unconvinced Admiral (James Robertson Justice) about the usefulness of small submarines in combat situations. The plan involves using these diminutive vessels to place explosives under the formidable German battleship "Tirpitz," which is secured within a Norwegian fjord. John Gregson and Donald Sinden are also part of this venture into enemy territory, where they face challenges from both the weather and the new technology they’re employing. The film conveys an understanding of the cramped environment and the essential cooperation it fosters, alongside highlighting the vulnerability of their equipment; interspersed with occasional humorous instances, this is a fairly absorbing story set during wartime.

Source on TMDB