On 5 December 1941, Squadron Leader A. E. Hill flew a photo-reconnaissance Spitfire along the Normandy coast at very low level and took a photograph of a clifftop near a village called Bruneval. In it, next to a villa, sits a large white dish.

British scientists had been arguing for months about what German radar could actually do, and why RAF bombers were being shot down at rates that suggested the night fighters were being pointed at them by something. The photograph gave them a target. It did not give them an answer.

So they decided to go and take one.

Why not just bomb it?

Because destroying the radar would have taught the British nothing. What Dr R. V. Jones and the scientific intelligence staff needed was the equipment itself: the frequencies it used, the way it scanned, how precisely it could point a night fighter, and above all whether it could be jammed or fooled.

A seaborne commando raid was ruled out. The coastal defences were heavy, a landing would be seen coming, and the Germans would have had ample time to wreck the set before anybody reached it. So the plan inverted itself: arrive from the air, where nobody was looking, and leave by sea.

One further piece of intelligence made the whole thing possible, and it did not come from an aeroplane. The French Resistance supplied details of the garrison and the defences, and confirmed something no photograph could: the beach below the cliff had not been mined.

The cinema projectionist who had never flown

Taking a radar apart under fire is not an infantry skill. The raiding force needed somebody who understood what he was looking at, so the RAF supplied Flight Sergeant Charles Cox, a radar technician who in civilian life had been a cinema projectionist.

Cox had never been in an aeroplane. He had never been on a ship. He was now expected to parachute into occupied France at night, photograph and sketch a piece of secret enemy equipment, dismantle the parts that mattered, and leave by boat, accompanied by ten Royal Engineers and specially built trolleys to carry the pieces down a cliff.

The rest of the force was C Company of the newly formed 2nd Parachute Battalion, drawn largely from Scottish regiments, commanded by Major John Frost, a name that would become considerably better known eighteen months later at Arnhem. The detachments were named after admirals: Nelson for the beach, Jellicoe, Hardy and Drake for the villa and the radar, Rodney in reserve.

The Whitleys go in

The raid was postponed after the rehearsal on 23 February, then went on 27 February, when the weather offered clear skies, good visibility and a full moon for the evacuation. The naval force sailed in the afternoon. The Whitleys of No. 51 Squadron lifted off from RAF Thruxton in Hampshire in the evening.

The Whitley was not a transport. It was a tired medium bomber with a nose-down cruising attitude, pressed into service as a parachute aircraft because Britain had nothing better. Paratroops exited through a hole cut in the floor, which is exactly as unpleasant as it sounds, and the aircraft's slipstream was notorious among early British airborne troops.

They crossed the Channel unmolested and then flew into heavy anti-aircraft fire at the French coast. Nothing was hit. The drop itself was close to perfect, with most of the force landing on the edge of the intended zone. The exception mattered: half of Nelson, the detachment responsible for clearing the evacuation beach, came down roughly two miles away.

Twenty minutes at the villa

Jellicoe, Hardy and Drake reached the villa without meeting anybody. Frost surrounded it and gave the order to open fire. One German guard was killed returning fire from an upstairs window; two more were captured, and under questioning revealed that most of the garrison was further inland. One of the prisoners was the Würzburg's operator, which was a considerable bonus.

Then the Germans in the surrounding buildings woke up, and the volume of fire rose sharply. Vehicles could be seen approaching from the woods. Frost's radios did not work, so he had no idea whether the beach had been taken.

Cox and the sappers worked through this. They photographed the set, then took it apart, loading the components onto the trolleys. Where dismantling was too slow under fire they simply tore parts out and took them anyway, on the reasonable assumption that the scientists at home could work backwards from whatever arrived.

The withdrawal was the worst part. The beach had not been cleared, and a German machine gun opened up on the descending raiders, severely wounding the company sergeant major. Frost sent Rodney and the men of Nelson who had arrived to deal with it, and the landing craft eventually came in. Two men were killed. Six were left behind and captured; all survived the war.

What it was worth

Churchill took a personal interest and convened the War Cabinet on 3 March to hear Frost and other participants describe it. On 15 May the London Gazette announced nineteen decorations. Frost received the Military Cross, Commander Cook the Distinguished Service Cross, and Cox the Military Medal. Pickard received a bar to his Distinguished Service Order later that month.

The technical yield was the point, and it was substantial. Examination of the captured components told the Telecommunications Research Establishment what Würzburg's weaknesses were, and contributed directly to the decision to deploy Window, the strips of aluminium foil that in July 1943 blinded the radars over Hamburg completely. A tunable jammer called Carpet, aimed specifically at Würzburg, followed.

There was also an entirely unintended dividend. Alarmed by the raid, the Germans ringed their Würzburg sites with belts of barbed wire to prevent a repeat. Barbed wire shows up beautifully on aerial photographs. In the run-up to D-Day, the defensive measure taken because of Bruneval made the radars easier to find and easier to destroy.

A memorial stands on the cliff at Bruneval today. Parts of the equipment brought back, including a captured flak pointing device, are on display at the Musée de l'Armée in Paris. And a former cinema projectionist who had never flown before that night went home with a Military Medal.

Sources: Imperial War Museum; Military Intelligence Museum; The Parachute Regimental Association; contemporary accounts of Operation Biting.