 | Richard Todd | ... | Wing Commander Guy Gibson, V.C., D.S.O., D.F.C. |
| Michael Redgrave | ... | Doctor B. N. Wallis, C.B.E., F.R.S. |
| Ursula Jeans | ... | Mrs. Wallis |
| Charles Carson | ... | Doctor |
| Stanley Van Beers | ... | Sir David Pye, C.B., F.R.S. |
| Colin Tapley | ... | Doctor W.H. Glanville, C.B., C.B.E. |
| Frederick Leister | ... | Committee Member |
| Eric Messiter | ... | Committee Member |
| Laidman Browne | ... | Committee Member |
| Raymond Huntley | ... | Official, National Physical Laboratory |
| Hugh Manning | ... | Official, Ministry of Aircraft Production |
| Patrick Barr | ... | Captain Joseph 'Mutt' Summers, C.B.E. |
| Edwin Styles | ... | Observer at trials |
| Hugh Moxey | ... | Observer at trials |
| Anthony Shaw | ... | R.A.F. Officer at trials |
| Basil Sydney | ... | Air Chief Marshal Sir Arthur Harris G.C.B., O.B.E., A.F.C. |
| Ernest Clark | ... | Air Vice-Marshal The Hon. Ralph Cochrane G.B.E., K.C.B., A.F.C. |
| Derek Farr | ... | Group Captain J.N.H. Whitworth, D.S.O., D.F.C. |
| Laurence Naismith | ... | Farmer |
| Harold Siddons | ... | Group Signals Officer |
| Frank Phillips | ... | B.B.C. Announcer |
| Brewster Mason | ... | Flt / Lt. R.D. Trevor-Roper, D.F.C., D.F.M. |
| Anthony Doonan | ... | Flt / Lt. R.E.G. Hutchison, D.F.C. |
| Nigel Stock | ... | Flying / Off. F.M. Spafford, D.F.C., D.F.M. |
| Brian Nissen | ... | Flt / Lt. A.T. Taerum, D.F.C. |
| Robert Shaw | ... | Flt / Sgt. J. Pulford, D.F.M. |
| Peter Assinder | ... | Plt / Off. G.A. Deering, D.F.C. |
| Richard Leech | ... | Squadron Leader H.M. Young, D.F.C. |
| Richard Thorp | ... | Squadron Leader H.E. Maudslay, D.F.C. |
| John Fraser | ... | Flight Lieutenant J.V. Hopgood, D.F.C. |
| David Morrell | ... | Flight Lieutenant W. Astell, D.F.C. |
| Bill Kerr | ... | Flight Lieutenant H.B. Martin, D.S.O., D.F.C., A.F.C. |
| George Baker | ... | Flight Lieutenant D.J.H. Maltby, D.S.O., D.F.C. |
| Ronald Wilson | ... | Flight Lieutenant D.J. Shannon, D.S.O., D.F.C. |
| Denys Graham | ... | Flying Officer L.G. Knight, D.S.O. |
| Basil Appleby | ... | Flight Lieutenant R.C. Hay, D.F.C. |
| Tim Turner | ... | Flight Lieutenant J.F. Leggo, D.F.C. |
| Ewen Solon | ... | Flight Sergeant G.E. Powell |
| Harold Goodwin | ... | Wing Comdr. Gibson's Batman |
| rest of cast listed alphabetically: |
| John Breslin | ... | Crew member (uncredited) |
| Edward Cast | ... | Crew Member (uncredited) |
| Richard Coleman | ... | RAF Officer (uncredited) |
| Peter Diamond | ... | Tail Gunner (uncredited) |
| Gerald Harper | ... | RAF Officer (uncredited) |
| Arthur Howard | ... | RAF Pay Clerk In NAAFI (uncredited) |
| Lloyd Lamble | ... | Collins (uncredited) |
| Philip Latham | ... | Flight Sergeant (uncredited) |
| Patrick McGoohan | ... | Guard on Door (uncredited) |
| Jack McNaughton | ... | Waiter (uncredited) |
| Nina Parry | ... | Barnes Wallace's daughter (uncredited) |
| Edwin Richfield | ... | RAF Officer (uncredited) |
