[1] He was working for an insurance company when he joined the Royal Australian Air Force (RAAF) Reserve in Adelaide on 5 July 1940, aged eighteen.

[3] After five of the aircraft had dropped their bouncing bombs on the Möhne, Shannon was preparing to make his attack on the dam when it gave way, so he carried on to the Eder with Gibson and three other Lancasters, captained by "Dinghy" Young, Henry Maudsley, and Les Knight.

[9] Detailed for the first bombing run at the Eder, Shannon took several attempts to familiarise himself with the area and line up his aircraft, so in the meantime Gibson ordered Maudsley to make his attack.

The operation was one of great difficulty and hazard, demanding a high degree of skill and courage and close co-operation between the crews of the aircraft engaged.

617 Squadron remained active as a special-duties unit operating against high-value targets, and Shannon took part in attacks on the Dortmund-Ems Canal and V-weapon sites with 12,000 lb (5,400 kg) bombs in the second half of 1943.

[3] The squadron made two attempts to destroy Dortmund-Ems, the first on the night of 14/15 September, aborting the mission with the loss of a Lancaster piloted by David Maltby.

[1][3] He married Section Officer Ann Fowler of the Women's Auxiliary Air Force at St Mark's parish church in London on 21 September.

[1] The couple had met at Scampton before the dams raid; Shannon proposed after returning from the mission and Ann accepted on the condition that he first shave his moustache.

[16][17] He was promoted to flight lieutenant two days later,[3] and awarded a bar to his DFC on 12 November for a "low level attack in adverse weather against heavy opposition".

He returned to the Lancaster on 5 June to drop "Window" as a part of the Allies' diversions ahead of the D-Day landings the following day, before again flying Mosquitos against V-weapon sites and in support of the Normandy invasion forces.

As they prepared to depart on one of their night missions, Cheshire commented on the beautiful sunset, to which Shannon replied, "I don't give a fuck about that, I want to see the sunrise".

[21][22] The full citation in The London Gazette read:[22] Since the award of a bar to the Distinguished Flying Cross, Squadron Leader Shannon has completed many sorties which he has executed with outstanding resolution and success.

He has at all times displayed courage and fortitude of a high order and his appreciation of the responsibilities entrusted to him have set a fine example to all.In October 1944, after a total of sixty-nine sorties, Shannon was taken off bomber operations and transferred to transport duties, initially with No.

[1][3] Having been employed as a trainee, he had gained promotion to refining coordinator with the company's East African subsidiary by the time he resigned in September 1961 to farm in Suffolk.

[1][26] On 8 April 1993, shortly before a planned fiftieth anniversary reunion of surviving Dambusters, Shannon died at Denmark Hill, London, following a stroke, and was buried beside Ann at Clifton Hampden, Oxfordshire.

[1][26] On 17 May 2008, the sixty-fifth anniversary of the Dambusters raid, a memorial to Shannon and two other South Australians who took part in the mission, bomb aimers Fred Spafford and Bob Hay, was unveiled in Adelaide in the presence of the airmen's families.

[27][28] In July 2009 Shannon's daughter Nikki made his medals, uniform, and logbook available to the Australian War Memorial (AWM) in Canberra, for long-term display.