 Steven MackintoshHimself - Narrator | Himself - Narrator |
 Brian DeaconGordon Welchman (voice) | Gordon Welchman (voice) |
| RRosamund WelchmanHerself - Gordon Welchman's Daughter | Herself - Gordon Welchman's Daughter |
| WW. Gordon WelchmanHimself - Ex-Head of Hut 6, Bletchley Park (1939-1941) (archive footage) | Himself - Ex-Head of Hut 6, Bletchley Park (1939-1941) (archive footage) |
| SSinclair McKayHimself - Author, 'The Secret Life of Bletchley Park' | Himself - Author, 'The Secret Life of Bletchley Park' |
| JJimmy ThirskHimself - Veteran, Hut 6 | Himself - Veteran, Hut 6 |
| AAsa BriggsHimself - Veteran, Hut 6 | Himself - Veteran, Hut 6 |
| JJane FawcettHerself - Veteran, Hut 6 | Herself - Veteran, Hut 6 |
| TTony ComerHimself - GCHQ Historian and Former Analyst | Himself - GCHQ Historian and Former Analyst |
| JJohn NaughtonHimself - Vice President, Wolfson College, Cambridge (as Prof John Naughton) | Himself - Vice President, Wolfson College, Cambridge (as Prof John Naughton) |
| JJohn ScarlettHimself - Chairman, Bletchley Park Trust, and Former Chief, MI6 (as Sir John Scarlett KCMG OBE) | Himself - Chairman, Bletchley Park Trust, and Former Chief, MI6 (as Sir John Scarlett KCMG OBE) |
| JJennifer WelchmanHerself - Gordon Welchman's Granddaughter | Herself - Gordon Welchman's Granddaughter |
| RRobert R. EverettHimself - Former President, The MITRE Corporation | Himself - Former President, The MITRE Corporation |
| EEric EllingsonHimself - Gordon Welchman's Colleague | Himself - Gordon Welchman's Colleague |
| LLarry HillHimself - Gordon Welchman's Colleague | Himself - Gordon Welchman's Colleague |
