This week, the 80 th anniversary of the raid will be subject to a range of commemorations. It is a word, and a mission, which has stuck fast to the British consciousness. Largely a success (though not to the extent claimed at the time), the raid made a celebrity of the squadron's commanding officer Guy Gibson, and landed his men a joyful nickname: “Dambusters”.

On the night of May 16-17 1943, 133 of them had flown 19 Lancaster bombers towards Germany as part of Operation Chastise – an inventive attack on the Moehne, Edersee and Sorpe Dams in the Ruhr valley, with Wallis’s new toys as a spear-tip. These dashing aviators called it “a splendid place remote from battle”. Petwood may have settled into a groove as a luxury retreat in the Lincolnshire village of Woodhall Spa, but it is still revered as having been the Officers’ Mess of the RAF’s 617 Squadron in 19. The source of the mirth is a table of guests and a bottle of rosé – but the idea of guffaws echoing down the years is not so far-fetched. Ghosts adrift on the early summer breeze? In a property built in 1905, which became a hotel in 1933, this is not impossible. I have slipped out of the restaurant and across the terrace to inspect it – and as I do so, I hear a cascade of exuberant laughter from the lounge. It looks oddly at home on the lawn of the Petwood Hotel, the evening sun slanting across it. But a sign in front reveals the truth – that this is a prototype of the famous “bouncing bomb” cleverly devised by the British genius Barnes Wallis to target German dams in the heat of the Second World War.

It looks, at first glance, like a heavy roller for a cricket pitch, idle between innings. A bomb before dinner seems a lot to digest, but there it is anyway – tucked beside the 1920s swimming pool which has been turned into a fountain.

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