John Treleaven was born in Croydon in Surry on 11 October 1927, the son of Charles John and Winifred Constance Treleaven (née Monckton). He was educated at Whitgift School in Croydon, Surrey.

He joined the Royal Navy and was appointed Midshipman (E) on 1 September 1945. He was promoted to Sub Lieutenant (E) on 1 October 1946 and served in the cruiser HMS DIDO, under training. In the October 1948 Navy List, he is recorded as an Acting Lieutenant (E), and in October and November 1950 he was serving in the battleship HMS VANGUARD.

He was appointed to HMS DOLPHIN ‘for the Submarine Course‘ on 7 January 1951. On 16 April 1951, his Training Class joined HMS AFFRAY at HMS DOLPHIN for sea training experience. AFFRAY was lost with all hands in the English Channel near the Hurd Deep overnight 16/17 April 1951.

John Treleaven was the husband of June Treleaven (née Kellett) – they had been married in Wandsworth in 1950.

NOTE: A collection of circa 1,000 letters between John Treleaven and his wife plus photos & press cuttings are held by the National Maritime Museum and an abridged collation by June Tower was published by the Glengarth Press, Kendal in 2009. (PBH 2662 in the Caird Library catalogue).