Operation Diver

Operation Diver was the British codename for countermeasures against the V-1 flying bomb campaign launched by the German Luftwaffe in 1944 against London and other parts of Britain. "Diver" was the codename for the V-1 itself. Modes of defence used against V-1s included anti-aircraft guns, barrage balloons, and fighter aircraft; also double agents planted false information about the success of targeting. Anti-aircraft guns proved the most effective form of defence in the later stages of the campaign, with the aid of radar-based technology and the proximity fuse. The bombing campaigns ended by the middle of 1944.

The "Diver Plan" was prepared in early 1944 following the first reports of the weapon in April 1943 and the discovery of its planned launch sites in late 1943. The plan had to be flexible enough to cover both the expected assault on Britain and the needs of the invasion of Europe.

When the German attack began, on the sixth day after the landings on the beaches of Normandy, the message "Diver, Diver, Diver" put the plan into action. Defences that had been guarding the embarkation ports for the invasion were redeployed against the V-1.

Anti-aircraft guns were redeployed in several movements: first in mid-June 1944 from positions on the North Downs to the south coast of England; then a cordon closing the Thames Estuary to attacks from the east. In September 1944 a new linear defence line was formed on the coast of East Anglia, and finally in December there was a further layout along the Lincolnshire-Yorkshire coast. The deployments were prompted by the ever-changing approach tracks of the missiles which were in turn influenced by the Allies' advance through Europe.

Anti-aircraft gunners found that such small, fast-moving targets were difficult to hit. At first, it took, on average, 2,500 shells to bring down a V-1. The average altitude of the V-1, between 2,000 and 3,000 feet (610 and 915 m), was in a narrow band between the optimum engagement heights for light (such as the 40mm Bofors guns) and heavy anti-aircraft weapons. These low heights defeated the rate of traverse of the standard British QF 3.7 inch mobile gun, and static gun installations with faster traverses had to be built at great cost. The development of centimetric (roughly 30 GHz frequency) gun laying radars based on the cavity magnetron and the development of the proximity fuze helped to neutralise the advantages of speed and size which the V-1 possessed. In 1944 Bell Labs started delivery of an anti-aircraft predictor fire-control system based around an analogue computer (supplanting the previous electro-mechanical Kerrison Predictor) just in time for use in this campaign.

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