A secret weapon intended to blast through the Nazis’ Normandy defences has been re-created to mark the 65th anniversary of the D-Day invasion.

A replica of the Great Panjandrum, a giant drum powered by rockets and carrying a ton of high explosives, will be set off this morning along the beach at Westward Ho! in North Devon, where the original trials took place.

The Great Panjandrum was never used in battle because it was judged too unpredictable and too dangerous to its own side. During testing in 1944, the prototype veered wildly off course and careered towards an audience of top brass and VIPs who were forced to flee from their vantage point on a shingle ridge. A cameraman filming the test had an even closer escape as the bomb rolled directly towards him, rockets firing in all directions.

The device was revived later for an episode of the BBC comedy Dad’s Army, in which it did just the same thing to great comic effect.

Ten workers from the Bristol fireworks company Skyburst have spent two days attaching dozens of rockets to the rims of a 2m (7ft) diameter replica made from a cable drum. The replica is expected to travel up to 500m (550 yards) at a speed of about 15mph.

Skyburst’s display director, Leigh Pittaway, ruled out filling it with explosives as the original had been. He said: “We thought about it, as we have the whole beach to ourselves, but decided it would create too many complications. We don’t want to kill any dogs or onlookers.”

The original Panjandrum would have been a formidable weapon, had it worked. It was devised by Nevil Shute Norway, later a bestselling novelist using the shortened name of Nevil Shute, but then a naval lieutenant. He trained as an aircraft engineer and had worked with Barnes Wallis, designer of the dam-busting bouncing bomb. Shute had been given the task, by the Admiralty’s Directorate of Miscellaneous Weapons Development, of finding a way of demolishing the German seafront defences before the invasion.

The weapon had to be launched from a landing craft and be able to survive a hail of fire before detonating at a designated spot. According to Shute’s calculations, the Panjandrum would travel at 60mph on its two 10ft diameter steel wheels, smashing its way through any obstacles, before blasting a hole in the 7ft concrete of the Atlantic Wall large enough to drive a tank through.

North Devon was chosen for the tests because its shallow sandy beaches resembled those of northern France.

The prototype Panjandrum was built in Leytonstone, East London, and transported to Devon under conditions of strict secrecy. But the military had failed to take into account that Westward Ho! and neighbouring Appledore were still popular with holidaymakers. When the time for the test came it was in front of an audience of hundreds of visitors and locals.

As the cordite rockets were fired up, the Panjandrum rolled off a landing craft and up the beach, but it veered off to one side and continued to do so during each attempt.

After weeks of adjustments Shute and his team felt they had solved the problem. A final demonstration was planned before an audience of senior officers and War Office officials.

Things began to go wrong almost as soon as the Great Panjandrum was unleashed. Clamps holding the powerful rockets broke and they went shooting off across the beach. Out of control, it hit a series of bumps and turned towards the pebble ridge.

Fortunately, before it could annihilate the assembled generals and admirals, it veered off again and toppled over before exploding.

The replica Panjandrum — named after a poem by Samuel Foote that ended with the line “till the gunpowder ran out at the heels of their boots” — was commissioned by the organisers of the Appledore Book Festival to mark the launch of their brochure.

A spokesman for the festival, Lyn Callaghan, said: “It does sound like something out of Dad’s Army but perhaps we shouldn’t laugh, as it was designed with a serious purpose in mind.”

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