James Caan as Cmdr. Richard Bolton, RNVR

David Sumner as Lt. Davies R.N.V.R

Norman Bowler as Sub-Lt. Pennington, RN

Paul Young as Leading Seaman Quentin

Brian Grellis as CPO Barquist X 3

William Dysart as Lt. Robert Talbot Gogan R.N.R.

John Kelland as Sub-Lt. Keith Willis, RNVR

Kenneth Farrington as CPO Boker Knowles

Carl Rigg as CPO Norman Kennedy

Steve Kirby as Leading Seaman X-2

Nick Tate as Leading Seaman X-1

George Pravda as Capt. Erlich of the 'Lindendorf'

Rupert Davies as Vice Admiral Redmayne (uncredited)

Keith Alexander as Sub. Lt. X-3

Diana Beevers as WRNS Officer (uncredited)

Paul Hansard as Cmdr. Steiner (uncredited)

Luke Hanson as German Lieutenant (uncredited)

Desmond Jordan as Naval Doctor (uncredited)

Dennis Mayers as Sub-Lieutenant on X-1 (uncredited)

Doug Robinson as Seaman in Self-defence Demonstration (uncredited)

George Roubicek as Redmayne's Flag Officer (uncredited)

Richard Steele as Captain in Redmayne's Office (uncredited)