[1] In his youth Crabb held many jobs but after two years training for a career at sea in the school ship HMS Conway he joined the merchant navy and the Royal Naval Reserve before World War II.

Initially, Crabb's job was to disarm mines that British divers removed, but eventually he decided to learn to dive.

[2] He was one of a group of underwater clearance divers who checked for limpet mines in Gibraltar harbour during the period of Italian frogman and manned torpedo attacks by the Decima Flottiglia MAS.

[3] On 8 December 1942, during one such attack, two of the Italian frogmen, Lieutenant Visintini and Petty Officer Magro, died, probably killed by small explosive charges thrown from harbour-defence patrol boats, a tactic said to have been introduced by Crabb.

He was also an investigating diver in the suspicious death of General Władysław Sikorski of the Polish Land Forces, whose B-24 Liberator aircraft crashed into the sea off Gibraltar in 1943.

Crabb moved to a civilian job and used his diving skills to explore the wreck of a Spanish galleon from the 1588 Armada, off Tobermory on the Isle of Mull.

[citation needed] In 1955, Crabb took frogman Sydney Knowles with him to investigate the hull of a Soviet Sverdlov-class cruiser to evaluate its superior manoeuvrability.

[7] According to Peter Wright in his book Spycatcher (1987), Crabb was sent to investigate Ordzhonikidze's propeller, a new design that Naval Intelligence wanted to examine.

On 29 April, under instructions from Rear Admiral John Inglis, the Director of Naval Intelligence,[6] the Admiralty announced that Crabb had vanished when he had taken part in trials of secret underwater apparatus in Stokes Bay on the Solent.

The British Prime Minister Anthony Eden disapproved of the fact that MI6 had operated without his consent in the UK (the preserve of the Security Service, "MI5").

[9] The Prime Minister told the House of Commons it was not in the public interest to disclose the circumstances in which Crabb was presumed to have met his end.

[10][11] A little less than 14 months after Crabb's disappearance, on 9 June 1957, a body in a diving suit was brought to the surface in their net by two fishermen off Pilsey Island in Chichester Harbour.

[13] He described the body as being clad in a faded green rubber frogman suit of a type issued to Royal Navy divers, and the remains of a white sweater.

[17] As neither Knowles nor Crabb's ex-wife nor a Lieutenant McLanahan, a Royal Navy torpedo officer from HMS Vernon, had been able to identify the body, Bridgman adjourned the inquest until 26 June to allow time for identification.

The ship operated in the conflict against the Netherlands over West Papua, and was later used as a floating detention centre for suspected communists during the Indonesian mass killings of 1965–66.

[22] After he was released from prison, the spy Harry Houghton wrote a book called Operation Portland in which he claimed that, in July 1956, his Russian handler, a man he knew as Roman, had told him how Crabb had died.

Houghton said that, shortly before the Soviet visit, he had been meeting Roman in a pub in Puncknowle, Dorset, and happened to see a friend who worked at the Underwater Detection Establishment with her boyfriend, who was a diver.

[23] According to Houghton's account, after assessing that divers might be planning some activity relating to Ordzhonikidze, the Soviet Navy arranged for six underwater sentries to watch the bottom of the ship, which had been fitted with wire jack-stays on either side to help them hold on.

Houghton advanced the theory that Crabb's mission was to plant a small limpet mine on Ordzhonikidze, the purpose of which was to detect whether the Soviet Navy was using the latest sonar technology.

On 16 November 2007, the BBC and the Daily Mirror reported that Eduard Koltsov, a Soviet frogman, claimed to have caught Crabb placing a mine on the hull of Ordzhonikidze and cut his throat.

In an interview for a Russian documentary film, Koltsov showed the dagger he claimed to have used, as well as an Order of the Red Star medal that he said had been awarded for the deed.

In particular, the archive documents did not confirm that Koltsov, a bus driver in Rostov-on-Don for 30 years, had been awarded the Order of the Red Star or was a Soviet Navy frogman.