Nazi WW2 V-1 flying bomb

Nazi V-1 flying bomb Fieseler Fi 103, Flak Zielgerät 76 (FZG-76)
V-1 at the National Air & Space Museum
Type	Guided missile
Place of origin	Nazi Germany
Service history
In service	1944-1945
Used by	Luftwaffe
Wars	World War II
Production history
Manufacturer	Fieseler
Specifications
Weight	2,150 kg (4,750 lb)
Width	5.3 meters (17 feet 6 inches)
Warhead	Amatol
Warhead weight	850 kg (1,870 lb)
Engine	Argus As 014 pulse jet engine
Operational range	250 km (150 miles)
Speed	630 km/h (390 mph) flying between 600 to 900 m (2,000 to 3,000 feet)
Guidance system	gyromagnetic compass based autopilot

The Nazi V-1 flying bomb (Nazi: Vergeltungswaffe 1) was the first guided missile used in war and the forerunner of today's cruise missile. The V-1 was developed at Peenemünde by the Nazi Luftwaffe during the Second World War. Between June 1944 and March 29, 1945, it was fired at targets in southeastern England and Belgium, London and Antwerp. V-1s were launched from "ski-jump" 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 Montange, as well as the launch sites, were bombed during Operation Crossbow

Design and development

The V-1 was designed by Robert Lussar 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 (241.4 km/h) for operation as it is commonly confused with the Lorin ram jet. The V1's Argus Schmidt pulse jet, also known as a resonant jet, could operate at zero airspeed due to the nature of its intake vane system and acoustically tuned resonant combustion chamber. Film footage of the V1 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 while the craft was stationary on the ramp. The low static thrust of the jet engine and very high stall speed of the wings meant that the craft could not take off under its own power in a practically short distance, and thus required a catapult launch or an airlaunch from a modified bomber. Take off speed was commonly attained by launching from a ground ramp, using a chemical or steam catapult which accelerated the V-1 to 200 mph, or from a moving aircraft such as the Heinkel He-111.

The V1'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 , where 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 of the V-1

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 gyromagnetic compass, which it also stabilized). There was a more sophisticated interaction between yaw, roll, and other sensors: a gyromagnetic compass (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 found when target range has 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 38 miles. When the count reached zero, a solenoid attached to a small guillotine was activated, cutting the air hose from the servo to the rear elevator and allowing a spring to fully depress the elevator causing the V-1 to 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.

With the counter determining how far the missile would fly; it was only necessary to launch the V1 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 V1 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 slow. Her recommendations of much higher landing speeds were then introduced in training new Reichenberg volunteer pilots. The Reichenbergs air-launched rather than fired from the catapult ramp as erroneously portrayed in "Operation Crossbow".

On 13 June 1944, the first V-1 struck London next to the railway bridge on Grove Road, Mile End, which now carries this plaque. Eight civilians were killed in the blast.

The conventional unpiloted V1 launch sites could theoretically launch about 15 bombs per day, although this was never consistently achieved; the record was 18 in one day. Only a quarter hit their targets due to a combination of defensive measures (see Countermeasures below), mechanical unreliability and guidance errors. Once the Allies had captured or destroyed the sites that were the principal launch points of V-1s aimed at England, the Nazis switched to missile launches aimed at 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.

Intelligence reports on the V-1 Flying Bomb

V-1 in flight

The codename Flak Zielgerät 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 V83 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. 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 Nazi scientists had achieved the needed accuracy to deploy the V-1 as a weapon, British intelligence had a very accurate assessment of it. British Intelligence also used the Double Cross System to provide false impact reports to Germany.

Countermeasures

The British defence against the Nazi 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 Nazi 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 defend against 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. 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 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.

A Spitfire using its wingtip to 'topple' a V-1 flying bomb

When V-1 attacks began in mid-June of 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 the hair-raising method of using the airflow over an interceptor's wing to raise one wing of the Doodlebug, 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 wing 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 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 fuse.

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.

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.

Assessment of the V-1

In early December 1944, an American General Clayton Bissell wrote a paper which argued strongly in favour of the V1 compared to conventional bombers

The following is a table he produced

Japanese versions

In 1943, an Argus pulse jet engine was shipped to Japan by Nazi 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 (Fi103R, 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" ("Cherry Blossom"), 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.

V-1 Post-war

V-1 Launch ramp recreated at Imperial War Museum, Duxford

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 Nazi 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 U.S. Navy conducted experiments to mount V-1s on submarines. This was called the KGW-1 Loon, which was an adaptation of the U.S. 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 Army Air Field 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 Nazi 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.