Operation Diver

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Operation Diver was the British codename for their countermeasures against the V-1 flying bomb campaign launched by the German Luftwaffe in 1944 against London and other parts of Britain. 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 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 analog computer just in time for use in this campaign.

Barrage balloons were also deployed against the missiles but the leading edges of the V-1's wings were equipped with balloon cable cutters and fewer than 300 V-1s are known to have been destroyed by hitting cables.

Fighters had been mobilized as part of Operation Diver. Most fighter aircraft were too slow to catch a V-1 unless they had a height advantage. Even when intercepted, the V-1 was difficult to bring down. Machine gun bullets had little effect on the sheet steel structure, and 20 mm cannon shells were explosive projectiles, which meant that detonating the warhead could destroy the fighter as well.

The V-1 was also nearly immune to conventional air-combat techniques because of its design, which eliminated the primary "one-shot stop" points of pilot, life-support and complex engine. A single hit on the pilot or oxygen system can force an abort or cause the destruction of a normal plane, but there is no pilot in a cruise missile. The reciprocating engines of WWII aircraft and the turbojet engines of today's fighters are also vulnerable, as a tiny nick in a quarter-inch oil line or one small shell fragment can destroy such engines. However, the Argus pulsejet could be shot full of holes and still provide sufficient thrust for flight. The only vulnerable point was the valve array at the front of the engine and the only one-shot stop points on the V-1 were the bomb detonators and the line from the fuel tank, three very small targets buried inside the fuselage. An explosive shell from a fighter's cannon or anti-aircraft artillery was the most effective weapon, if it could hit the warhead.

When the attacks began in mid-June of 1944 there were fewer than 30 Tempests in 150 Wing to defend against them. Few other aircraft had the low-altitude speed to be effective. Early attempts to intercept V-1s often failed but techniques were rapidly developed. These included the hair-raising method of using the airflow over an interceptor's wing to raise one wing of the Doodlebug, by sliding the wingtip under the V-1's wing and bringing it to within six inches (15 cm) of the lower surface. Done properly, the airflow would tip the V-1's wing up, overriding the buzz bomb's gyros and sending it into an out of control dive. At least three V-1s were destroyed this way.

The Tempest wing was built up to over 100 aircraft by September; P-51 Mustangs and Griffon-engined Spitfire XIVs were polished and tuned to make them almost fast enough, and during the short summer nights the Tempests shared defensive duty with Mosquitoes. Specially modified P-47Ms (half their fuel tanks, half their 0.5in {12.7 mm} machine guns, all external fittings, and all their armour plate removed) were also pressed into service against the V-1 menace. There was no need for radar — at night the V-1's engine could be heard from 16 km (10 miles) or more away, and the exhaust plume was like a beacon. Wing Commander Roland Beamont had the 20mm cannons on his Tempest harmonised at 300 yards (275 m). This was so successful all other aircraft in 150 Wing were thus modified.

In daylight, V-1 chases were chaotic and often unsuccessful until a special defence zone between London and the coast was declared in which only the fastest fighters were permitted. Between June and mid-August 1944, the handful of Tempests shot down 638 flying bombs. One Tempest pilot, Squadron Leader Joseph Berry of No. 501 (Tempest) Squadron, downed fifty-nine V-1s, and Wing Commander Roland Beamont destroyed 31.

Next most successful was the Mosquito (428), Spitfire XIV (303), and Mustang, (232). All other types combined added 158. The still-experimental jet-powered Gloster Meteor, which was rushed half-ready into service in July 1944 to fight the V-1s, had ample speed but suffered from a readily-jammed cannon and accounted for only 13.

By mid-August 1944, the threat was all but overcome—not by aircraft but by the sudden arrival of two enormously effective electronic aids for anti-aircraft guns, both developed in the USA by the MIT Rad Lab: radar-based automatic gunlaying (using, among others, the SCR-584 radar) and the proximity fuze. Both of these had been requested by AA Command and arrived in numbers, starting in June 1944, just as the guns reached their free-firing positions on the coast.

Seventeen per cent of all flying bombs entering the coastal 'gun belt' were destroyed by guns in the first week on the coast. This rose to 60 per cent by 23 August and 74 per cent in the last week of the month, when on one extraordinary day 82 per cent were shot down. The rate increased from one V-1 for every 2,500 shells fired to one for every hundred.

A deception concerning the V-1 was also played on the Germans using double agents. MI5 (by way of the famed Double Cross System) had these agents provide Germany with damage reports for the June 1944 V-1 attacks which implied that on average the bombs were travelling too far, while not contradicting the evidence presumed to be available to German planners from photographic reconnaissance of London. In fact the bombs had been seeded with radio-transmitting samples to confirm their range but the results from these samples were ignored in favour of the false witness accounts and many lives may have been saved by the resulting tendency of future V-1 bombs to fall short.

[edit] References

• King, Benjamin; Kutta, Timothy (1998). IMPACT. The History of Germany's V-Weapons in World War II. Rockville Center, New York: Sarpedon Publishers. ISBN 978-1-885119-51-3.
• Ramsay,Winston; 'The Blitz Then & Now'(Volume 3). 1990 Battle of Britain Prints International. ISBN 978-0-900913-58-7

[edit] Further reading

• Vergeltungswaffe V-Weapons – From Daniel Green's World War II Air Power website; contains descriptions and film sequences (AVI format)
• The V-Weapons – From Marshall Stelzriede's Wartime Story website; with June 1944 UK/US news reports on V-1 attacks
• Fi-103/V-1 "Buzz Bomb" – From the Luftwaffe Resource Center website, hosted by The Warbirds Resource Group; with 42 photos
• The Lambeth Archives includes description and sound of V1 and provides the means of finding where bombs fell on particular districts.