Two of her crew, Lt Antony Fasson, from Jedburgh in the Scottish Borders, and Able Seaman Colin Grazier, from Tamworth, Staffordshire, swam to the sinking U-559 against survivors of her crew swimming towards the Petard to be rescued. They clambered down the conning tower and handed documents from the captain's cabin to a Naafi assistant, Tommy Brown, from North Shields Tyneside, who joined them inside the U-boat after jumping aboard while the Petard was briefly alongside. Brown made three trips carrying bundles of documents up the conning tower ladder to be passed into a whaler that had by that time come alongside.
Meanwhile Fasson and Grazier had tied a signals machine (the Enigma) to a line from the conning tower, and Fasson shouted to the men at the top, "Box coming up. Be careful as it looks to me as if it is important." Seconds later he and Grazier were trapped as the U-boat sank with water pouring down the conning tower.
The box which cost two lives was not vitally important. Bletchley Park, the wartime decoding centre sometimes called after its signals section Station X, already had several Enigmas and had worked out the wiring of the latest four-rotor model. But the documents taken safely to the Petard in waterproof wrapping proved invaluable.
They enabled Bletchley Park codebreakers to read U-boat signals again after 10 critical months when U-boat signals intelligence was totally blacked out. This had begun when the Germans added a fourth rotor to the Enigma coding machine at the start of an all-out U-boat offensive.
Their capture was the primary factor in the success of the Allied navies' defeat of the U-boat wolf-packs as they were close to achieving their aim of starving Britain into seeking an armistice and preventing the build- up of American forces for the invasion of Fortress Europe. This decisive victory in the Battle of the Atlantic, the crucial campaign of the war, directly resulted from the HMS Petard's epic action against the U-559 in the eastern Mediterranean.
The captured codebooks allowed Ultra signals intelligence to give locations and the operational intentions of the U-boat packs. It was estimated that 500,000 tons of shipping were saved during the first months of 1943. Convoys were routed around areas where U-boat packs were lying in wait, and U- boats were sunk at such a rate that Admiral Doenitz, the U-boat commander, withdrew the remnant of his U-boat packs from the Atlantic.
Within six weeks the tide had been turned, and the Battle of the Atlantic won. The build-up for the invasion of Normandy in 1944 was able to go ahead. Otherwise, it might have had to be postponed till 1946, and the atomic bombs might have been used in Europe.
The two men who gave their lives to achieve this immense victory were posthumously awarded the civilian award of the George Cross instead of the top military award of the Victoria Cross because the Admiralty was worried that the military award would attract German curiosity, risking another change in the Enigma which had taken so long to break.
The sacrifice of these men's lives and the gallantry of their crewmates was the key in turning the course of the war. It would have put HMS Petard's name to keep the Germans unaware that Enigma messages were being broken. HMS Petard was broken up in 1967 long before her fame might have saved her to be revered alongside Nelson's Victory in Portsmouth dockyard.
Stephen Harper is the author of `Capturing Enigma - how HMS Petard seized the German Enigma codes' (Sutton Publishing, pounds 14.99)Reuse content