First broadcast 21st June 1973.
HMS Hero's mission is to test out a new underwater submarine system, Mongoose, with a simulated war game against the US Navy.
Donald Burton - Commander Mark Nialls
David Savile - Lieutenant Commander Beaumont
Don Henderson - Master at Arms Heron
Rex Robinson - Lieutenant Commander Junnion
Norman Eshley - Lieutenant Last
James Cosmo - Leading Regulator Fuller
Christopher Coll - Lieutenant Boswall
Charles Bolton - Bunny
Brian Peck - Tolliday
Victor Winding - Slater
Andrew McCulloch - Cutler
Roger Tallon - Barnes
Stephen Stacey - Loftus
David Troughton - Doc Pitman
David Griffith - Blackie (as Mark Griffith)
