Admiral Sir Simon Alastair Cassillis Cassels, (5 March 1928 – 6 March 2019) was a senior Royal Navy officer who served as Second Sea Lord and Chief of Naval Personnel from 1982 to 1986.

Naval career Cassels joined the Royal Navy in 1947. He was Navigation Staff Officer to Chief of the Polaris Executive from 1963 to 1966,The Impact of Polaris – The Origins of Britain's Seaborne Nuclear Deterrent by Captain J. E. Moore, Richard Netherwood Ltd, 1999, and went on to command in 1972.HMS Fearless 1970–1972

Cassels became Assistant Chief of the Naval Staff (Operational Requirements) in 1978,Whitaker's Almanack 1980 and was promoted to vice-admiral on 18 November 1980. He was appointed Flag Officer, Plymouth and Admiral Superintendent at Devonport in 1981,Whitaker's Almanack 1982 and Second Sea Lord and Chief of Naval Personnel as well as President of the Royal Naval College, Greenwich in 1982.Birthdays The Times, 5 March 2008 Promoted full admiral in November 1984, he retired in 1986.

Cassels was appointed a Commander of the Order of the British Empire (CBE) in the 1976 Birthday Honours, and a Knight Commander of the Order of the Bath (KCB) in the 1982 Birthday Honours.

Later life In retirement Cassels's activities included serving as Chairman of the Modern Apprentices Advisory Committee.Apprenticeships Head Enjoys a Tasty Visit to VT Plus Training VTi – Newspaper of the VT Group, Winter 2004/5 He lived at Exton in Hampshire.Winchester City Council, Planning Development Control Committee p. 417

Cassels died on 6 March 2019, aged 91.Cassels

Family Cassels was married to Jill.Hundreds line streets for returning heroes Portsmouth News, 29 January 2008

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