The V-1 flying bomb (German: Vergeltungswaffe 1, lit. 'Vengeance Weapon 1') was an early cruise missile. Its official Reich Aviation Ministry (RLM) name was Fieseler Fi 103 and its suggestive name was Höllenhund (hellhound). It was also known to the Allies as the buzz bomb or doodlebug and Maikäfer (maybug).
The V-1 was the first of the Vergeltungswaffen (V-weapons) deployed for the terror bombing of London. It was developed at Peenemünde Army Research Center in 1942 by the Luftwaffe, and during initial development was known by the codename Kirschkern (cherry stone). Due to its limited range, the thousands of V-1 missiles launched into England were fired from launch sites along the French (Pas-de-Calais) and Dutch coasts or by modified Heinkel He 111 aircraft.
The Wehrmacht first launched the V-1s against London on 13 June 1944, one week after (and prompted by) Operation Overlord, the Allied landings in France. At times more than one hundred V-1s a day were fired at south-east England, 9,521 in total, decreasing in number as sites were overrun until October 1944, when the last V-1 site in range of Britain was overrun by Allied forces. After this, the Germans directed V-1s at the port of Antwerp and at other targets in Belgium, launching another 2,448 V-1s. The attacks stopped only a month before the war in Europe ended, when the last launch site in the Low Countries was overrun on 29 March 1945.
As part of Operation Crossbow, operations against the V-1, the British air defences consisted of anti-aircraft guns, barrage balloons and fighter aircraft, to intercept the bombs before they reached their targets, while the launch sites and underground storage depots became targets for Allied attacks including strategic bombing.
In 1944 a number of tests of this weapon were apparently conducted in Tornio, Finland. On one occasion, several Finnish soldiers saw a German plane launch what they described as a bomb shaped like a small, winged aircraft. The flight and impact of another prototype was seen by Finnish frontline soldiers; they noted that its engine stopped suddenly, causing the V-1 to descend sharply, and explode on impact, leaving a crater 20–30 metres (66–98 ft) wide. These V-1s became known to Finnish soldiers as "flying torpedoes".
In 1935 Paul Schmidt and Georg Hans Madelung submitted a design to the Luftwaffe for a flying bomb. It was an innovative design that used a pulse-jet engine, while previous work dating back to 1915 by Sperry Gyroscope relied on propellers. While employed by the Argus Motoren company, Fritz Gosslau developed a remote-controlled target drone, the FZG 43 (Flakzielgerät-43). In October 1939 Argus proposed Fernfeuer, a remote-controlled aircraft carrying a payload of one ton, that could return to base after releasing its bomb. Argus worked in co-operation with C. Lorenz AG and Arado Flugzeugwerke to develop the project. However, the Luftwaffe declined to award them a development contract. In 1940, Schmidt and Argus began cooperating, integrating Schmidt's shutter system with Argus' atomized fuel injection. Tests began in January 1941, and the first flight made on 30 April 1941 with a Gotha Go 145. On 27 February 1942 Gosslau and Robert Lusser sketched out the design of an aircraft with the pulse-jet above the tail, the basis for the future V-1.
Lusser produced a preliminary design in April 1942, P35 Erfurt, which used gyroscopes. When submitted to the Luftwaffe on 5 June 1942, the specifications included a range of 300 km (186 miles), a speed of 700 km/h (435 mph), and capable of delivering a 500-kilogram (1⁄2-long-ton) warhead. Project Fieseler Fi 103 was approved on 19 June, and assigned code name Kirschkern and cover name Flakzielgerät 76 (FZG-76). Flight tests were conducted at the Luftwaffe's Erprobungsstelle coastal test centre at Karlshagen, Peenemünde-West.
Erhard Milch, State Secretary in the Reich Ministry of Aviation and Inspector General of the Air force, awarded Argus the contract for the engine, Fieseler the airframe, and Askania the guidance system. By 30 August Fieseler had completed the first fuselage, and the first flight of the Fi 103 V7 took place on 10 December 1942, when it was airdropped by a Fw 200. Then on Christmas Eve, the V-1 flew 900 m (1,000 yd), for about a minute, after a ground launch. On 26 May 1943 Germany decided to put both the V-1 and the V-2 into production. In July 1943 the V-1 flew 245 kilometres (152 mi) and impacted within a kilometre (1,100 yards) of its target.
The V-1 was named by Das Reich journalist Hans Schwarz Van Berkl in June 1944 with Hitler's approval.
The V-1 was designed under the codename Kirschkern (cherry stone) by Lusser and Gosslau, with a fuselage constructed mainly of welded sheet steel and wings built of plywood. The simple, Argus-built pulsejet engine pulsed 50 times per second, and the characteristic buzzing sound gave rise to the colloquial names "buzz bomb" or "doodlebug" (a common name for a wide variety of flying insects). It was known briefly in Germany (on Hitler's orders) as Maikäfer (May bug literally "May" + "chafer") and Krähe (crow).
The Argus pulsejet's major components included the nacelle, fuel jets, flap valve grid, mixing chamber venturi, tail pipe, and spark plug. Compressed air rather than a fuel pump forced gasoline from the 640 L (140 imp gal; 170 US gal) fuel tank through the fuel jets which consisted of three banks of three atomizers. These nine atomizing nozzles were in front of the air inlet valve system where it mixed with air before entering the chamber. A throttle valve, connected to altitude and ram pressure instruments, controlled fuel flow. Schmidt's spring-controlled flap valve system provided an efficient straight path for incoming air. The flaps momentarily closed after each explosion, the resultant gas compressed in the venturi chamber, and its tapered portion accelerated the exhaust gases creating thrust. The operation proceeded at a rate of 42 cycles per second.
Beginning in January 1941, the V-1's pulsejet engine was also tested on a variety of craft, including automobiles and an experimental attack boat known as the Tornado, in which a boat loaded with a 700 kg (1,500 lb) warhead was steered towards a target ship either by remote control or by a pilot who would leap out of the back at the last moment. The Tornado was assembled from surplus seaplane hulls connected in catamaran fashion. Ultimately insufficient Argus 014 pulse-jets were available as all production was allocated to the V-1 missile program. The engine made its first flight aboard a Gotha Go 145 on 30 April 1941.
The V-1 guidance system used a simple autopilot developed by Askania in Berlin to regulate altitude and airspeed. A pair of gyroscopes controlled yaw and pitch, while azimuth was maintained by a magnetic compass. Altitude was maintained by a barometric device. Two spherical tanks contained compressed air at 6.2 megapascals (900 psi), that drove the gyros, operated the pneumatic servomotors controlling the rudder and elevator, and pressurized the fuel system.
The magnetic compass was located near the front of the V-1, within a wooden sphere. Shortly before launch, the V-1 was suspended inside the Compass Swinging Building (Richthaus). There the compass was corrected for magnetic variance and magnetic deviation. The RLM at first planned to use a radio control system with the V-1 for precision attacks, but the government decided instead to use the missile against London. Some flying bombs were equipped with a basic radio transmitter operating in the range of 340–450 kHz. Once over the channel, the radio would be switched on by the vane counter, and a 120-metre (400 ft) aerial deployed. A coded Morse signal, unique to each V-1 site, transmitted the route, and impact zone calculated once the radio stopped transmitting.
An odometer driven by a vane anemometer on the nose determined when the target area had been reached, accurate enough for area bombing. Before launch, it was set to count backwards from 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 odometer. This odometer triggered the arming of the warhead after about 60 km (37 mi). 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 put 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 people under the flight path to the impending impact.