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V-1 flying bomb

The Fieseler Fi 103, better known as V-1 (German: Vergeltungswaffe 1) was an early cruise missile used during World War Two. The V-1 was developed at Peenemünde by the German Luftwaffe during the Second World War. Between June 1944 and March 29, 1945, it was fired at population centers such as London and Antwerp. V-1s were launched from "ski" launch sites along the French (Pas-de-Calais) and Dutch coasts until the sites were overrun by Allied forces. The underground V-1 storage depots at Saint-Leu-d'Esserent, Nucourt and Rilly-la-Montagne, as well as the launch sites, were bombed during Operation Crossbow.

Design and development

The V-1 was designed by Robert Lusser of the Fieseler company and Fritz Gosslau from the Argus engine works, with a fuselage constructed mainly of welded sheet steel and wings built similarly or of plywood. The simple pulse jet engine pulsed 50 times per second, and the characteristic buzzing sound gave rise to the colloquial names "buzz bomb" or "doodlebug" (after an Australian insect).

It is a common myth that the V-1's pulsejet engine needed a minimum airspeed of 150 mph (240 km/h) for operation as it is commonly confused with the Lorin ramjet. The V-1's Argus Schmidt pulsejet, also known as a resonant jet, could operate at zero airspeed owing to the nature of its intake vane system and acoustically tuned resonant combustion chamber. Film footage of the V-1 always shows the distinctive pulsating jet exhaust of a fully running engine before the catapult system is triggered. The engine would always be started first (using a compressed air line) while the craft was stationary on the ramp. The low static thrust of the jet engine and very high stall speed of the small wings meant that the craft could not take off under its own power in a practically short distance, and thus required an aircraft catapult launch or an airlaunch from a modified bomber aircraft such as the Heinkel He-111. On the ground, takeoff speed was attained by using a chemical or steam catapult which accelerated the V-1 to 200 mph (320 km/h).

The V-1's pulse jet engine was also tested on a variety of craft, including an experimental attack boat known as the "Tornado". The unsuccessful prototype was a version of a Sprengboot, in which a boat loaded with explosives was steered towards a target ship and the pilot would leap out the back at the last moment. The Tornado was assembled from surplus seaplane hulls connected in catamaran fashion with a small pilot cabin on the cross beams. The Tornado prototype was a noisy underperformer and was abandoned in favour of more conventional piston engined craft.

Guidance system

The V-1 guidance system used a simple autopilot to regulate height and speed. A weighted pendulum system provided fore-and-aft attitude measurement to control pitch (damped by a gyrocompass, which it also stabilized). There was a more sophisticated interaction between yaw, roll, and other sensors: a gyrocompass (set by swinging in a hangar before launch) gave feedback to control each of pitch and roll, but it was angled away from the horizontal so that controlling these degrees of freedom interacted: the gyroscope stayed trued up by feedback from the magnetic field, and from the fore and aft pendulum. This interaction meant that rudder control was enough without a separate banking mechanism.

A countdown timer driven by a vane anemometer on the nose determined when target range had been reached, accurately enough for area bombing. Before launch the counter was set to a value that would reach zero upon arrival at the target in the prevailing wind conditions. As the missile flew, the airflow turned the propeller and every 30 rotations of the propeller counted down one number on the counter. This counter triggered the arming of the warhead after about 60 km (38 miles). When the count reached zero, two detonating bolts were fired. Two spoilers on the elevator were released, the linkage between the elevator and servo was jammed and a guillotine device cut off the control hoses to the rudder servo, setting the rudder in neutral. These actions led the V-1 into a steep dive. While this was originally intended to be a power dive, in practice the dive caused the fuel flow to cease, which stopped the engine. The sudden silence after the buzzing alerted listeners that the V-1 would impact soon. The fuel problem was quickly fixed and by the time the last V-1 fell, the majority had impacted under full power.

With the counter determining how far the missile would fly, it was only necessary to launch the V-1 with the ramp in the rough direction and the autopilot controlled the rest.

Operation and effectiveness

The first test flight of the V-1 was in late 1941 or early 1942 at Peenemünde.

A myth arose that early guidance and stabilisation problems were resolved by a daring test flight by Hanna Reitsch in a V-1 modified for manned operation. The myth entered popular consciousness from Hanna's fictional exploits in the George Peppard film Operation Crossbow.

Hanna's first flights in the modified V-1 Fieseler Reichenberg were late in the war when she was asked to work out why test pilots were unable to land it and had died in landing attempts. Her discovery after simulated landing attempts at high altitude where there might be air space to recover, was that the craft had an extremely high stall speed and the previous pilots with little high speed experience had attempted their approaches much too slowly. Her recommendations of much higher landing speeds were then introduced in training new Reichenberg volunteer pilots. The Reichenbergs were air-launched rather than fired from the catapult ramp as erroneously portrayed in "Operation Crossbow".

The conventional launch sites could theoretically launch about 15 V-1s per day, but this rate was difficult to achieve on a consistent basis; the maximum rate achieved was 18. Overall, only about 25% of the V-1s hit their targets, the majority being lost because of a combination of defensive measures (see Countermeasures below), mechanical unreliability or guidance errors. With the capture or destruction of the launch facilities used to attack England, the V-1s were employed in attacks against strategic points in the Low Countries, primarily the port of Antwerp.

The earliest experimental versions of the V-1 were air-launched. Most operational V-1s were launched from static sites on land, but from July 1944 to January 1945 the Luftwaffe launched approximately 1,176 from modified Heinkel He 111 H-22s flying with the Luftwaffe's 3rd Bomber Wing or Kampfgeschwader 3 (the so-named "Blitz Wing") flying over the North Sea. Research after the war estimated a 40% failure rate of air-launched V-1s, and the He-111s used in this role were extremely vulnerable to night fighter attack, as the launch lit up the area around the aircraft for several seconds.

Late in the war several air-launched piloted V-1s, known as Reichenbergs, were built, but never used in combat. There were plans, not carried into practice, to use the Arado Ar 234 jet bomber to launch V-1s either by towing them aloft or by launching them from a "piggy back" position atop the aircraft.

Almost 30,000 V-1s were made. Approximately 10,000 were fired at England; 2,419 reached London, killing about 6,184 people and injuring 17,981. The greatest density of hits were received by Croydon, on the SE fringe of London.

Antwerp (Belgium) was hit by 2,448 V-1s from October 1944 to March 1945.

Intelligence reports

The codename Flakzielgerät 76 - "Flak aiming apparatus" helped to hide the nature of the device, and it was some time before references to FZG 76 were linked to the V-83 pilotless aircraft (an experimental V-1) that had crashed on Bornholm in the Baltic and to reports from agents of a flying bomb capable of being used against London. Especially the Polish Home Army intelligence contributed information on V-1 construction and a place of development (Peenemünde). Initially British experts were skeptical of the V-1 because they had considered only solid fuel rockets, which could not attain the stated range of 130 miles (209 km). However they later considered other types of engine, and by the time German scientists had achieved the needed accuracy to deploy the V-1 as a weapon, British intelligence had a very accurate assessment of it.

Countermeasures

Lacking adequate photo reconnaissance, the Germans relied in part on reports from their agents to determine if the range settings in the guidance system were correct. British Intelligence used the Double Cross System to provide Germany with false reports showing impacts northwest of the city center. Many V-1s were then programmed for too short a run and fell well southeast of the city.

The British defence against the German long-range weapons was Operation Crossbow. 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 changes to the approach tracks of the V-1 as launch sites were overrun by the Allies' advance.

On the first night of sustained bombardment, the anti-aircraft crews around Croydon were jubilant - suddenly they were downing unprecedented numbers of German bombers; most of their targets burst into flames and fell when their engines cut out. There was great disappointment when the truth was announced. Anti-aircraft gunners soon found that such small fast-moving targets were, in fact, very difficult to hit. The cruising altitude of the V-1, between 2,000 and 3,000 feet (600 to 900 m), was just above the effective range of light anti-aircraft guns, and just below the optimum engagement height of heavier guns. The altitude and speed were more than the rate of traverse of the standard British QF 3.7 inch mobile gun could cope with, and faster-traversing static gun emplacements had to be built at great cost. The development of centimetric gun-laying radars based on the cavity magnetron and of the proximity fuse helped to counter the V-1's high speed and small size. In 1944, Bell Labs started delivery of an anti-aircraft predictor fire-control system based around an analog computer, just in time for the Allied invasion of Europe.

Eventually some 2,000 barrage balloons were deployed, in the hope that V-1s would be destroyed when they struck the balloons' tethering cables. The leading edges of the V-1's wings were fitted with cable cutters, and fewer than 300 V-1s are known to have been brought down by barrage balloons.

Fighters were mobilized to intercept the V-1, but most fighter aircraft were too slow to catch a V-1 unless they had a height advantage, allowing them to gain speed by diving (a late version of the Republic Aviation's P-47 Thunderbolt was stripped of all excess weight and given a more powerful engine, to fill this role). Solid machine gun bullets had little effect on the V-1's sheet steel structure, and if an explosive cannon shell detonated the warhead, the explosion could destroy the attacking fighter. The first interception of a V-1, by F/L JG Musgrave of No. 605 Squadron RAF, took place on the night of 14/15 June 1944.

The Defence Committee expressed some doubt as to the ability of the Royal Observer Corps to deal adequately with this new threat, but the ROC's Commandant Air Commodore Finlay Crerar assured the committee that the ROC could again rise to the occasion and prove its alertness and flexibility. He oversaw plans for handling the new threat, codenamed by the RAF and ROC as "Operation Totter".

Observers at the coast post of Dymchurch identified the very first of these weapons and within seconds of their report the anti-aircraft defences were in action. This new weapon gave the ROC much additional work both at posts and operations rooms. Eventually RAF controllers actually took their radio equipment to the two closest ROC operations rooms at Horsham and Maidstone and vectored fighters direct from the ROC's plotting tables. The critics who had said that the Corps would be unable to handle the fast-flying jet aircraft were answered when these aircraft on their first operation were actually controlled entirely by using ROC information both on the coast and at inland.

The V-1 also lacked the primary points of vulnerability of conventional aircraft: pilot, life-support, and a complex engine. Hits to the pilot, oxygen system, or complex reciprocating engines of a piloted aircraft by a bullet or small shell fragment can destroy its fighting capability, but the V-1's Argus pulsejet provided sufficient thrust for flight even if damaged. The only vulnerable point of the Argus was the valve array at the front of the engine. The V-1's only one-shot stop points were the two bomb detonators and the line from the fuel tank--three very small targets buried inside the fuselage. A direct hit on the warhead by an explosive shell from a fighter's cannon, or a very close anti-aircraft shell explosion, were the most effective forms of gunfire.

When V-1 attacks began in mid-June 1944, there were fewer than 30 Tempests, the only aircraft with the low-altitude speed needed to be effective against the V-1. They were assigned to No. 150 Wing RAF. Early attempts to intercept and destroy V-1s often failed, but improved techniques soon emerged. These included using the airflow over an interceptor's wing to raise one wing of the V-1, by sliding the wingtip to within six inches (15 cm) of the lower surface of the V-1's wing. If properly executed, this manoeuvre would tip the V-1's wing up, overriding the gyros and sending the V-1 into an out-of-control dive. At least three V-1s were destroyed this way.

The Tempest fleet was built up to over 100 aircraft by September; P-51 Mustangs and Griffon-engined Spitfire XIVs were tuned to make them almost fast enough, and during the short summer nights the Tempests shared defensive duty with de Havilland Mosquitoes. 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 visible from a long distance. Wing Commander Roland Beamont had the 20 mm cannons on his Tempest harmonised (regulated) at 300 yards (275 m) (i.e. set to fire at the same spot 300 yards ahead). This was so successful that all other aircraft in 150 Wing were thus modified.

In daylight, V-1 chases were chaotic and often unsuccessful until a special defence zone was declared between London and the coast, in which only the fastest fighters were permitted. Between June and 5 September 1944, the handful of 150 Wing Tempests shot down 638 flying bombs, with No. 3 Squadron RAF alone claiming 305. One Tempest pilot, Squadron Leader Joseph Berry of No. 501 (Tempest) Squadron, shot down 59 V-1s, and Wing Commander Roland Beamont destroyed 31.

Next most successful were the Mosquito (428), Spitfire XIV (303), and Mustang (232). All other types combined added 158. Even though it was not fully operational, the jet-powered Gloster Meteor was rushed into service with No. 616 Squadron RAF to fight the V-1s. It had ample speed but its cannons were prone to jamming, and it shot down only 13 V-1s.

In mid-1944 the V-1 threat was drastically reduced by the arrival of two electronic aids for anti-aircraft guns requested by AA Command, both developed in the USA by the MIT Rad Lab after the British John Randall and Harry Boot had invented the cavity magnetron and provided it to them free of charge: radar-based automatic gunlaying (using the SCR-584 and other radars), and the proximity fuze.

These electronic aids arrived in quantity from June 1944, just as the guns reached their firing positions on the coast. Seventeen percent of all flying bombs entering the coastal 'gun belt' were destroyed by guns in their first week on the coast. This rose to 60% by 23 August and 74% in the last week of the month, when on one day 82% were shot down. The rate improved from one V-1 destroyed for every 2,500 shells fired initially, to one for every 100. This still did not stem the problem, however, and the threat was not properly contained until the launch sites could be captured by infantry.

In late 1944 a radar-equipped Vickers Wellington bomber was modified for use by the RAF's Fighter Interception Unit as what would now be described as an Airborne Early Warning and Control aircraft. It operated at an altitude of some 4,000 feet over the North Sea to control Mosquito fighters intercepting He 111s flying from Dutch airbases and carrying out airborne launches of the V-1.

By September 1944, the V-1 threat to England ended when all launch sites were overrun by the advancing Allied Armies. 4,261 V-1s had been destroyed by fighters, anti-aircraft fire and barrage balloons.

The last enemy-action incident of any kind on British soil occurred at Datchworth in Hertfordshire on 29th March when a V-1 was used.

Assessment

In early December 1944, an American General Clayton Bissell wrote a paper which argued strongly in favour of the V-1 compared to conventional bombers

The following is a table he produced

Blitz (12 months) vs V-1 flying bombs (2¾ months)
Blitz V-1
1. Cost to Germany
Sorties 90,000 8,025
Weight of bombs tons 61,149 14,600
Fuel consumed tons 71,700 4,681
Aircraft lost 3,075 0
Men lost 7690 0
2. Results
Houses damaged/destroyed 1,150,000 1,127,000
Casualties 92,566 22,892
Rate casualties/bombs tons 1.6 1.6
3. Allied air effort
Sorties 86,800 44,770
Planes lost 1,260 351
Men lost 2,233 805

Japanese versions

In 1943, an Argus pulse jet engine was shipped to Japan by German submarine. The Aeronautical Institute of Tokyo Imperial University and the Kawanishi Aircraft Company conducted a joint study of the feasibility of mounting a similar engine on a piloted plane. The resulting design was based on the Fieseler Fi-103 Reichenberg (Fi 103R, a piloted V-1), and was named Baika ("ume blossom").

Baika never left the design stage but technical drawings and notes suggest that two versions were under consideration: an air-launch version with the engine mounted under the fuselage, and a ground-launch version that could take off without a ramp.

Intelligence reports of the new "Baika" weapon are rumored to be the source of the name given to the Yokosuka MXY-7, a rocket-propelled suicide plane better known as the "Baka Bomb." However, as baka means "fool" in Japanese, and the MXY-7 was officially designated the "Ohka," the true origin is unknown. The MXY-7 was usually carried by the G4M2e version of the Mitsubishi G4M "Betty" naval bomber, then the pilot lit the solid-fuel rockets and guided his flying bomb into a ship. During the Boeing B-29 firebomb attacks on Japanese cities, the Baka was deployed against American bombers.

Another Japanese Fi 103 version was the Mizuno Shinryu, a proposed rocket-powered kamikaze aircraft design, but it was not built.

Post-war

After the war, the armed forces of France, the Soviet Union and the United States experimented with the V-1.France: The French produced copies of the V-1 for use as target drones. These were called the CT-10 and were smaller than the V-1 with twin tail surfaces. The CT 10 could be ground launched using a rocket booster or from an aircraft. Some CT-10s were sold to the UK and USA.Soviet Union:

The Soviet Union captured V-1s when they overran the Blizna test range in Poland. The 10Kh was their copy of the V-1, later called Izdeliye 10. Initial tests began in March 1945 at a test range in Tashkent with further launches from ground sites and from aircraft of improved versions continuing into the late 1940s. The inaccuracy of the guidance system compared to new methods such as beam-riding and TV guidance saw development end in the early 1950s. The Soviets also worked on a piloted attack aircraft based on the Argus pulse jet engine of the V-1 which began as a German project, the Junkers EF 126 Lilli , in the latter stages of the war. The Soviet development of the Lilli ended in 1946 after a crash that killed the test pilot.United States: The US Navy conducted experiments to mount V-1s on submarines. This was called the KGW-1 Loon, which was an adaptation of the US Army's JB-2 Doodle Bug. The JB-2, built by Republic Aviation (airframe) and Ford Motor Company (pulsejet engine), was reverse-engineered by inspecting V-1 wreckage found in England and was first flight-tested less than four months after the first V-1 attack. While the first flights were from Eglin AAF, Florida, extensive testing was also done at Wendover AAF in Utah, launching only a few hundred feet from the sheds where delivery methods for the first atomic bombs were being developed under Project Alberta. The JB-2 was intended as a weapon in the planned invasion of Japan, but Japan surrendered and the invasion did not take place. Following the war, testing at Wendover continued, including comparison tests between the original German missile and the American copy. Later, preliminary design work was done on a small atomic warhead to be fitted to the JB-2, but it was never built. The US briefly considered using the Loon in the Korean War against North Korean targets.

Operators

See also

References

Bibliography

  • Haining, Peter. The Flying Bomb War. Robson Books, 2002. ISBN 1-86105-581-1.
  • Jones, R.V. Most Secret War. Hamish Hamilton, London, 1978. ISBN 0 241 89746 7
  • Kay, Anthony L. Buzz Bomb, Monogram Close-Up 4. Boylston, MA: Monogram Aviation Publications, 1977. ISBN 0-914144-04-9.
  • King, Benjamin and Kutta, Timothy. IMPACT. The History of Germany's V-Weapons in World War II. Rockville Center, New York: Sarpedon Publishers, 1998. ISBN 1-885119-51-8.
  • Ramsay, Winston; The Blitz Then & Now(Volume 3). Battle of Britain Prints International, 1990. ISBN 0-900913-58-4
  • Zaloga, Steven; V-1 Flying Bomb 1942-52. Osprey Publishing, 2005. ISBN 1-84176-791-3.

Notes

External links

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