The Mediterranean, 1941/42 - Axis forces are using frogmen and manned torpedoes to attack previously impregnable harbours. The Allied forces need to come up with something to answer this threat, which they find in the form of Lt. Lionel "Buster" Crabb.

Laurence Harveyas Lieutenant "Buster" Crabb, R.N.V.R.
Michael Craigas Leading Seaman Knowles
Dawn Addamsas Third Officer Jill Masters, W.R.N.S
John Clementsas The Admiral
Sidney Jamesas Chief Petty Officer Thorpe
Alec McCowenas Able Seaman Morgan
Nigel Stockas Able Seaman Fraser
Ian Whittakeras Ordinary Seaman Thomas
Arnoldo Foàas Tomolino
Gianna Maria Canaleas Conchita