McCarthy, then a Flight Lieutenant, was tall and powerfully built (he had been a Coney Island lifeguard in civilian life) with a ready flow of picturesque language; he wore both "USA" and "Canada" shoulder flashes on his uniform. Like many US volunteers who wanted to fly with the RAF he had joined the Royal Canadian Air Force, gaining his pilot's wings and a commission under the joint Air Training Plan.
He had been picked by Gibson because of his exceptional service on another Lancaster squadron, No 97, for which he had been awarded the Distinguished Flying Cross. The citation said that he had flown as captain of aircraft on sorties to heavily defended German and Italian targets, including three attacks on Berlin. He had "set an example of high courage and efficiency". In No 617 Squadron he was to do likewise.
On the night when its crews took off to attack six Ruhr dams with Dr Barnes Wallis's "bouncing bomb" (codenamed Upkeep), McCarthy's target was the Sorpe earth dam, and all his determination was required even to get airborne. His favourite Lancaster, AJ-Q, proved to be unserviceable; so he made for the reserve aircraft, AJ-T, only to find that it had no compass deviation card. He rushed to the flight office, where the missing card was extracted from the instrument section. AJ-T got airborne just after 2201 hours - some 34 minutes late - and McCarthy belted across the North Sea at 200mph to make up for lost time.
By flying very low - a technique which No 617 sqadron pilots had perfected - he managed to evade Luftwaffe night fighters and reached the target area shortly after 0015 hours. But it was 40 minutes later on their 10th run over the head of the dam that the bomb-aimer, Sergeant G.L. Johnson, was satisfied and released the Upkeep weapon. There was a tremendous explosion and a plume of water rose up, but only the top 15-20 feet of the dam wall had crumbled. Not until 0300 hours when AJ-T was some 20 minutes away from Scampton - having deviated through compass failure over very hostile areas like the Hamm marshalling yards (where laconic North American tones over the radio transmitter were heard to observe that the defences didn't need flak at that height - only to change the points) did the crew report that their mine had exploded in contact with the Sorpe Dam, causing "a small breach".
For his part in Operation Chastise, when eight out of 19 Lancasters were lost, McCarthy was awarded the Distinguished Service Order. Then in April 1944 he received a bar to his DFC, the citation saying that since his DSO award he had taken part in difficult and hazardous operations at low level - displaying exemplary skill and courage, which "combined with his unfailing devotion to duty had contributed much to the successes achieved".
As an Acting Squadron Leader he became one of the three Flight Commanders on No 617 squadron - all of whom, survivors of the Dams Raid, were ordered to rest after an attack on V-Weapon sites in France on 6 July 1944.
Joe McCarthy remained in Britain after the war, test-flying many captured German aircraft at the Royal Aircraft Establishment, Farnborough. He then returned to Canada where he became a test pilot for the RCAF, later commanding successively a Nato flying training school and a maritime patrol squadron. As a Wing Commander he was on the staff of the Allied Commander-in-Chief Atlantic at Norfolk, Virginia, before retiring to Virginia Beach.
Joseph Charles McCarthy, air force officer: born St James, Long Island 31 August 1919; DSO 1943; DFC 1943, and bar 1944; married (one son, one daughter); died 6 September 1998.