[2] Propulsion machinery consisted of two Admiralty Standard Range 16 VMS diesel generators, and two 3,000-shaft-horsepower (2,200 kW) electric motors, each driving a 7-foot diameter (2.1 m) three-bladed propeller at up to 400 rpm.

During Onyx's construction there was an explosion which took the life of a shipyard worker and severely wounded communist union leader Barry Williams.

[2] Onyx was ordered after a previous Oberon-class submarine of the same name (laid down by Chatham Dockyard in 1962) was transferred to the Royal Canadian Navy as HMCS Ojibwa before launching in February 1964.

[6] During one of these missions, Onyx hit an uncharted pinnacle while submerged at 150 feet (46 m) and suffered minor damage to her bow.

Contrary to some reports,[10] after the British cancelled Operation Mikado, there was never a plan to use Onyx to land the SAS in order to destroy Argentina's remaining stockpile of Exocet missiles.

A small party from HMS Exploit gave her a send off recognising her contribution to the Navy and country in the Cold War and Falklands conflict.

On 30 April 2014 she was sailed from Barrow in tow for the Clyde and berthed at Rosneath amid continued uncertainty as to whether at least part of Onyx might be preserved.