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Rebuilding Hitler’s ‘Supergun’

On Channel 4 this Sunday, Dr Hugh Hunt will show viewers how Hitler’s notorious ‘V-3 Supergun’ worked, and what killed Lieutenant Joseph Kennedy Junior on the secret mission to foil the Nazi plot to destroy London.

The Second World War story of the Vergeltungswaffe 3 – literally, a weapon of reprisal – is well known. Less well understood is how the massive gun worked and whether it could achieve its ultimate objective. Encouraged by arms manufacturers, Hitler championed plans for a 25-barrelled cannon that could bombard London from secret emplacements nearly 100 miles away, in the Pas-de-Calais, northern France. No gun had ever fired that distance.

Lieutenant Joseph Kennedy Junior ( © Earl P. Olsen)

Engineers sought to tackle this through ‘booster’ charges along the barrel of the gun, adding velocity to the projectile – which could then reach and devastate London.

In the Channel 4 documentary, Building Hitler’s Supergun: The Plot to Destroy London, Dr Hunt, Fellow of Trinity and Reader at the Department of Engineering, performs a series of experiments.

The big mystery was how it worked. To get up to speed the Germans used booster charges along the barrel. But how do you get the booster charges to go off one after the other in perfect synchronicity? If a charge goes off too early it will slow down the projectile, or worse, blow up the gun. If it goes off too late then it won’t add to the speed of the shell.

The documentary also pinpoints why the US Navy Aphrodite mission to blow up the huge installation in northern France failed. Tragically, this operation killed Lieutenant Joseph Kennedy – elder brother to JFK and the son who had been groomed to be President of the USA – and his co-pilot, Lieutenant Wilford John Willy.

Completely without warning, the plane exploded over the Blyth Estuary in Suffolk only minutes after it had taken off from an airfield in Norfolk. Their bodies were never found, such was the violence of the explosion.

Dr Hunt testing the bomber's arming mechanism

On the day of the mission from RAF Fersfield, 12 August 1944, electronics officer Earl Olsen repeated his fears of a fatal flaw in the arming system of the bomber – which was supposed to detonate the explosives after the crew had parachuted to safety. In the documentary, Dr Hunt rebuilds and tests the electronics that so worried Olsen.

Recent documents have been found that show that the bomb-arming mechanism was flawed and that efforts to make it safe only exacerbated the hazards. In our documentary we show that solenoids used for arming the bombs were likely to have overheated causing premature detonation.

Hitler’s supergun was never fired. In fact, the emplacement hewn inside a hill in Mimoyecques had been abandoned after it was damaged in 1944 by RAF bombers equipped with a powerful new weapon. Built by POWs and German workers, the massive complex made an impression on Dr Hunt when he visited more than 70 years later.

It is huge – cavernous – and cold. It is hard to imagine that it was dug out by hand – by slave labour.

In July 1944, Lancaster bombers – from the Dambusters’ Squadron – attacked the site with ‘Tallboy’ bombs. Developed by Barnes Wallis, the brains behind the bouncing bomb, these massive weapons were designed to be dropped from a great height and to trigger a small earthquake. Dr Hunt explained what happened:

Six Tallboys were dropped on Mimoyecques and the network of tunnels, the foundations, bunkers and munitions stores were all damaged beyond repair. The genius of Barnes Wallis cannot be overstated. He worked out the right shape for the nose cone of the Tallboy so that it would be aerodynamic while approaching the speed of sound, and at the same time strong enough to penetrate 15 metres underground. He discovered that if the fins were tilted slightly the bomb would spin, fast enough to stabilise it in flight, and while drilling into the ground.

Building Hitler’s Supergun: The Plot to Destroy London will be broadcast on Channel 4 at 8pm on Sunday 22 November. It follows Dr Hunt’s other award-winning documentaries, including Dambusters: Building the Bouncing Bomb and Escape from Colditz. Dr Hunt, who was awarded the 2015 Rooke Award for the public promotion of engineering, is continually inspired by documentary making:

It’s only by trying to recreate the hardware and doing the experiments for real that you realise just how amazing and inventive these people were. It wasn’t just a desk job!

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