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 Lieutenant Alastair Mars during his time as captain of HMS Unbroken | |
| Born | 1 January 1915 St John's, Dominion of Newfoundland |
| Died | 12 March 1985 Ipswich, Suffolk, England |
| Allegiance |  United Kingdom |
| Service |  Royal Navy |
| Years of service | 1932–1952 |
| Rank | Lieutenant Commander |
| Commands | HMS Unbroken HMS Thule |
| Battles / wars | World War II
|
| Awards | DSO DSC and bar |
| Other work | Author of several autobiographies and novels. |
Lieutenant Commander Alastair Campbell Gillespie Mars, DSO, DSC and Bar (1 January 1915 – 12 March 1985) was a Royal Navy World War II submarine commander.
In 1952, he was court martialled and dismissed from the service under controversial circumstances and pursued a career as an author.