Osborn Allen was born in Nowshera, Bengal in 1925, the only son of Lieutenant Colonel Harold Allen, DSO and Mrs Allen. He joined the Royal Navy as a Cadet ‘for Engineering Duties‘ on 1 September 1944. He was promoted to Midshipman (E) on 1 May 1945 and on passing out from training he was awarded two months advancement. He was promoted to Sub Lieutenant (E) on 1 August 1946. According to the October 1948 Navy List he had been appointed to the cruiser HMS GLASGOW, although no date of his appointment is available.

Osborn Allen joined HMS DOLPHIN for the Submarine Training Class for Engineer Officers in 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, following an accident whilst dived.

His Next of Kin were his parents of Red House, Heywood Lane, Tenby, Pembrokeshire.