V-2 Credit - © Mark Wade Media Gallery

The V-2 ballistic missile (known to its designers as the A4) was the world's first operational liquid fuel rocket. It represented an enormous quantum leap in technology, financed by Nazi Germany in a huge development program that cost at least $ 2 billion in 1944 dollars. 6,084 V-2 missiles were built, 95% of them by 20,000 slave labourer in the last seven months of World War II at a unit price of $ 17,877. As many as 3,225 were launched in combat, primarily against Antwerp and London, and a further 1,000 to 1,750 were fired in tests and training. Despite the scale of this effort, the inaccurate missile did not change the course of the war and proved to be an enormous waste of resources. The British, Americans, and Russians launched a further 86 captured German V-2's in 1945-1952. Personnel and technology from the V-2 program formed the starting point for post-war rocketry development in America, Russia, and France.

The V-2 and the atomic bomb both were world-shifting technological quantum leaps. Both were developed in enormous haste; used the first technical solutions that worked; consumed a considerable portion of the country's war budget; and were only available in the last months of the war. Unlike the atomic bomb, the V-2 was not a war-changing weapon, and the resources devoted to it undoubtedly hurt rather than helped the German war effort. At war's end the Allies seized tonnes of documents, hundreds of experts, and dozens of V-2 missiles. Despite this, many basic facts regarding the V-2 remain unclear. There are major discrepancies between the number reportedly built, the number said to have been fired, and the number impacting in the target zone. These call into question the claimed production rates, reliability, and accuracy of the V-2 as a weapon.

The V-2 - Not Ready for Production

When Wernher von Braun was recruited to assist Walter Dornberger in the development of liquid fuel rockets for the German Army in August 1932, only the tiniest baby steps toward development of rocket motors had been taken by the German Society for Spaceship Flight (VfR). The VfR had fired only the most rudimentary of pressure-fed water-cooled combustion chambers, generating only 60 kgf at a specific impulse of 173 seconds. After 28 months of development, Von Braun was able to demonstrate the A2, a small rocket generating 300 kgf to the German Army. But this design of December 1934 still used the primitive cooling method of having the combustion chamber and rocket nozzle immersed in the fuel tank. After another three years, in December 1937, Von Braun launched the A3, which was supposed to be a prototype for the A4 war rocket. The A3 had a thrust of 1500 kgf, but still used the same cooling method and had a specific impulse of only 195 seconds. The A3 was a miserable failure - it was clear that the control system and aerodynamics were completely wrong. Detailed design of the A4 was postponed until aerodynamics and control systems could be worked out in a new subscale design, the A5.

Development of the rocket engine for the A4 was also bedeviled with difficulties. The A4 would need an engine of 25 tonnes thrust. Eventually, through a seven-year process of trial and error, a fuel-cooled rocket engine of 1.5 tonnes thrust and a specific impulse of 215 seconds was perfected. But all attempts to scale this engine up to the 25 tonnes thrust required for the A4 met insurmountable combustion instability problems. Finally an interim solution to produce test A4 missiles was found - clustering 18 of the 1.5 tonne combustion chambers, feeding into a common mixing chamber. In fact this immensely complex 'interim' design had to be pressed into production.

Development of the aerodynamics and control systems for the V-2 took hundreds of tests of the A5 - in wind tunnels, air-drops, and powered flights. This was also a grueling trial and error process, for there was little theory and no practical experience in supersonic aerodynamics. A missile had to be controlled when rising vertically at near zero speed, where aerodynamic surfaces would be ineffective. Then it had to remain controllable and stable at subsonic, transonic, and supersonic speeds up to Mach 4. It was not until mid-1942, ten years after development had started, that the first test A4 was launched. But at least it was shown that the long development process using the A5 had produced workable aerodynamic and control solutions.

The turbopumps to feed the propellants to the engines proved relatively easy - to Von Braun's surprise, high-volume low-weight pumps were already well developed for fire engines. The other structural elements were well within the allowable mass. Ed Heinemann of Douglas Aircraft was probably the greatest low-weight aircraft engineer that ever lived. He designed a single-stage-to-orbit launch vehicle in 1946, and relates the following story of a 1961 meeting with Von Braun:

…I went to see Wernher Von Braun in Huntsville, Alabama, on a different matter…In the discussion that followed …. Wernher [was asked] why he used a 26 percent structural weight fraction ratio on the V-2.

"Well," Von Braun said, "I built the structure strong enough to hold together, and frankly, it just came out that way."

We (at Douglas) had differed from Wernher in our approach in that we worked backwards. We began with a weight and designed components to remain within that weight. Wernher, on the other hand, designed the components and then arrived at a weight. His circumstances were far different from ours, of course, since he was building a weapon which had to be very rugged. If there was a lesson in the [Douglas 1946] satellite project, it was that by starting out with a clean piece of paper and a different approach, suitable results could be achieved, regardless of what approach others might have taken to reach the same goal.

The final area of completely new technology was the guidance system. How could a missile with a range of 320 km be guided accurately to its target? It seemed only a radio beam guidance system could provide the necessary accuracy, but the V-2 developers had to take a backseat to development of such systems for the German bomber and interceptor forces. Therefore they settled for a control system that oriented the missile along a pre-determined path in a vertical plane pointed at the target. The system used accumulating accelerometers to determine when the missile had reached the correct velocity and then cut off the engine. It was thought that this would provide sufficient accuracy, although operations would indicate otherwise...

Hitler delayed the decision to put the V-2 into production for three years, from 1939 to 1942. Dornberger laments this delay repeatedly in his memoirs, claiming his rocket team could have fielded a weapon that would have changed the course of the war if only it had been available earlier. However, given the difficulties in the development of the V-2, this seems doubtful. Even with the 1942 go-ahead, the V-2 was nowhere near a production design. Getting it into production concurrently with development was a nearly insurmountable problem - 65,000 changes were made to the initial production drawings. Tests of the first production missiles began in early 1944. Mysterious in-flight disintegrations of the missiles resulted in an 80% failure rate. These were found to have multiple causes, and the last of the several fixes to the missile was not introduced in the production line until November 1944. By then 60% of all the V-2's that ever would be built had already been shipped out.

The V-2 - What are the real numbers?

Production and operation of the V-2 was run by the dreaded SS. Final assembly was accomplished by slave labourers housed in the Dora concentration camp next to the Mittelwerk underground factory at Nordhausen. It is therefore not surprising that most official documentation in regarding production and firing rates was destroyed. Available information paints a confusing picture:

• How many V-2's were built? Prototype V-2's were built at the Peenemuende launch and development center. The original production plans called for the V-2 to be built at factories at Peenemuende, the Zeppelinwerke at Friedrichshafen, the Raxwerke at Wiener Neustadt, and at seven combined production-launch bunkers in Pas-de-Calais and Cherbourg. 12,000 were to be built at a peak rate of 900 per month. On 17 August 1943 Peenemuende was massively bombed. In the following weeks raids were also made (coincidentally) against all of the other production sites. The Germans (erroneously) concluded that their V-2 production infrastructure had been compromised. They decided to move all final assembly of the V-2 to underground facilities at Nordhausen (Mittelwerke) and Ebensee (Projekt Zement). Only Nordhausen would be put into use before the end of the war.

  Prior to August 17, at least 41 rockets had been built at Peenemuende. The bombing created delays, but V-2's continued to be built at Peenemuende well into 1944, peaking at fifty missiles in September 1943. Production deliveries began at Nordhausen in January 1944. Different sources give numbers that vary by around 5%. For this discussion we will assume the final total production as 314 for Peenemuende and 5,770 for Nordhausen, a total of 6,084.

• How many V-2's were fired? For Peenemuende, a detailed record exists only for the first 32 V-2's launched. Although occasional launches after early July 1943 have been anecdotally documented, there seems to be no tally as to how many were tested during the course of 1944. Production sample and training firings were moved to Heidelager, in Poland, in November 1943. A total of 139 are documented as having been fired from there. These firing units had to move away from the Russian advance to Heidekraut in August 1944, and a further 246 documented missiles were fired from that location. V-2 operational units are said variously to have launched between 2,970 and 3,280 missiles between September 1944 and April 1945. In his memoirs, Dornberger says that 4,300 V-2's were fired in all. Using either number, taking known rejection rates into account, there is a substantial discrepancy - 1,000 to 1,750 missiles - between V-2's said to have been produced and V-2's documented as fired. David Irving, author of The Mare's Nest, suggests that most of this number were fired as test or practice rounds from Peenemuende and Heidelager.

  Dornberger states that it was found that a missile had to be fired within three days of production in order to ensure that perishable materials had not deteriorated. This implies that any V-2's manufactured had to be fired within a month at the most or reworked or scrapped. A comparison of cumulative production and cumulative known firings shows that as many as 1,750 rockets would have to have been test fired by November 1944 at a peak rate of about ten per day in May - June 1944. This is not beyond the realm of possibility, but there is no evidence for it. Anecdotal evidence indicates that such a firing rate of test missiles was the exception, not the rule. More likely is the possibility that nearly all of the early production missiles, lacking the fixes necessary to make them reliable, were recycled back into the factory. They were either scrapped, cannabilised, renumbered - effectively double-counted. Officially there were only 231 such missiles, but perhaps the pressure to meet Hitler's demands for higher production led to a much more substantial recycling. Such a deception by his own SS commanders would certainly not have been documented on paper...

• What was the reliability and accuracy of the V-2? Dornberger's memoirs proudly note the improvement as fixes were made to solve the in-flight explosion problems. V-2 missile reliability as tested increased from 30% in January 1944 to 70% immediately before combat firings began in September 1944. Dornberger claims it reached nearly 100% after the final technical fix was introduced into production in December 1944. Some authors credit combat missiles with a reliability of 80% to 90%, quite remarkable considering that they were inherently fragile, built underground by slave labour, and transported in incredibly difficult conditions to the launch sites. No total tally exists, but detailed figures for certain months and places show losses all along the distribution chain. Of 6,001 missiles submitted for final inspection, 231 were missiles previously rejected and reworked (4%). Unit records for December 1944 to February 1945 show 12% of the missiles received by the units were rejected on the spot as unsuitable for firing. Of the launches made in the same months, 10% were observed as launch failures within sight of the launch units themselves. British post-war studies would seem to indicate that another 12% landed in the sea or remote areas of the British land mass and were not recorded as impacts. This indicates that at least one third of the V-2's either never launched due to quality problems or crashed within 100 km of the launch point.
• What was the accuracy of the V-2? This question reduces to one of philosophy - if a missile misses the aim point by half the range, does that shot count against the missile's accuracy calculation or is it a failure, counted in the reliability calculation? Tests of prototype V-2's in 1943 indicated a 4.5 km CEP (circular error probable - the radius within which 50% of the shots impact). 100% of the shots fell within 18 km of the target. A radio beam guidance update system was introduced in December 1944, which in tests produced a 2 km CEP. In reality, in the campaign against Britain, 518 rockets were recorded as falling in the Greater London Air Defence Zone of 1225 fired, implying an average CEP of 12 km.

  Part of this lack of accuracy was attributable to a skilful British disinformation campaign. Nazi agents in Britain were the only source of information to the Germans as to where the missiles actually hit. Most of these agents had been turned by British intelligence and were sending back false reports as to the impact points of the rockets. These false reports indicated that the missiles were going long and impacting beyond London. As a result of corrections due to this false information, the German average impact point moving farther and farther east as the campaign went on. The average impact point for the entire campaign ended up on the eastern edge of the Greater London Air Defence Zone.

  Had accurate post-attack reports been available to the Germans, the CEP would have been more like 6 km, reinforcing Dornberger's claim that by the end of the campaign the missile was close to achieving its tested accuracy. Without the British disinformation campaign, the number of the Allied victims of the V-2 would have been more than doubled, demonstrating the effectiveness of that operation. However even at its best accuracy made the V-2 was hugely cost-ineffective. Its primary purpose could only be psychological, and in that it suffered in comparison to the V-1.

More detail on the development of the V-2 follows:

• V-2 Trivia
• V-2 Statistics
• V-2 Chronology

V-2 Trivia

• Hitler personally determined the V-2 targets (London, Antwerp, Paris, etc.) He rejected use of the rocket on the Eastern Front
• Von Braun was opposed to the establishment of a V-2 production plant at Peenemuende.
• As early as 1935, in a meeting with General Becker on planning for the A4 and Peenemuende, Von Braun advocated spaceflight as the ultimate program objective.
• Dornberger served under General von Brauchtisch in the Reichswehr. Von Brauchtisch was able to protect the Peenemuende team from takeover attempts by industry, the Air Force, the SS, etc. Speer also was important as a protector. But later even he came into conflict with other groups in the Third Reich, and couldn't prevent the final takeover of the V-2 programme by the SS.
• The film cooling used in the V-2's engine had performance penalties but was necessary, since high-quality metals for the nozzle throat were not available at the time
• Oberth's daughter was killed in a liquid oxygen plant explosion.
• Dornberger set up the first school for the rocket troops at Koslin.
• The Schwimmweste project involved a floating Wasserfall test stand, and was not connected to the submarine-towed V-2 as indicated in some histories.
• Rocket team member Konrad Dannenberg obtained his early rocketry experience through involvement with Pullenberg's underground rocket group in Hannover. He also witnessed the Opel rocket rail car tests and heard Max Valier lecture.
• The rocket engineer's efficiency was reduced significantly due to their dispersal after the raid Allied raid on Peenemuende of 17 August 1943
• There were serious problems in getting production drawings out that worked. Parts were often defective. Walter "Papa" Riedel was unfairly dismissed over the problem. In all 65,000 changes were made to the missile design between the decision to put it into production and the end of the war.
• Von Braun wanted another year of development on the A4.
• Dornberger criticized von Braun for not being focused.
• Originally it was planned that a horizontal production line be established at Peenemuende in the Versuchsserienwerk (research series production factory).
• The A7 was a subscale version of the winged A9. Considerable resources were expended on it before its cancellation in 1943.
• The Long Range Bombardment Commission observed a 'fly-off' of the V-1 and V-2 on a visit to Peenemuende. The Commission originated in a Luftwaffe plan to kill the Army's V-2. Instead both missiles were approved for production.
• The Peenemuende engineers were under constant threat of being drafted and sent to the front. Reports and results were expected from each engineer without pause in order to justify his draft exemption.
• Combustion/injection research by an American NACA engineer was used in solving V-2 engine problems. Konrad Dannenberg had seen the NACA report at Hannover while working with Pullenberg.
• As far back as the V-2, Von Braun advocated underestimating costs in order to sell projects to the government.
• In mass production, the V-2's combustion chambers and turbopumps were fabricated and tested separately. Based on these test results, they were matched according to their characteristics and mated on the assembly line.
• Reisig, on the Dornberger staff, had to convey endless changes in the missile to the launch troops.
• The use of highly qualified Peenemuende research and development staff for V-2 production was seen as a big waste of effort.
• Walter Riedel was a talented engineer but his lack of academic qualifications led to conflicts with the graduate engineers on the rocket team. Confusingly, he was replaced by Walther Riedel.
• The He-112 rocket aircraft accident was due to base pressure flame suction. This was a valuable experience when the same effect was observed on the A4.
• After takeover of the project by Kammler and the SS, Dornberger's responsibilities were limited to testing ground equipment and continuing development firings of the V-2 from the Blizna SS range in Poland.
• Rudolph and von Braun laid out their plans for spaceflight at the Kummersdorf officer's club in 1935. These studies were the basis for Von Braun's publications in the 1950s on Mars exploration.
• Thiel deserved much of the credit for development of the V-2 engine. His death in the bombing raid of 17 August 1943 was a big loss. If he had lived, the Peenemuende team could have succeeded in completing development of the Mischduese injector plate engine. This had combustion instability problems that could not be overcome before the end of the war. As a result the complex 18 injector 'basket-head' design had to be put into production instead.
• All Wasserfall launches were made from Greifswalder Oie
• Kurt Debus was in the SS, as was Von Braun.
• Von Braun decided that the V-2 central records would be saved and hidden. All other files and secondary records were intentionally burned in order to give the central records value as a bargaining chip with the Allies after the war.
• There were no significant tension in the V-2 engineering leadership over Nazi Party or political questions.
• The Wolman Doppler tracking system for the A4 was modified to command V-2 engine cut-off by radio. Later the method of calculating the moment of cut-off was changed to integration of inputs from accelerometers due to fear of Allied jamming of the command signals.
• Von Braun was forced to wear his SS uniform by Dornberger for the meeting with Himmler.
• The in-house laboratory concept for guidance-and-control development at Peenemuende was largely forced by the circumstances of heavy time-pressure and lack of experience in the industry. Its creation was not due to the ideology of the engineers.
• Von Braun was more than a manager at Peenemuende. He also contributed valuable technical solutions, notably in the guidance and control areas.
• Von Braun often exhibited anti-Nazi attitudes.
• Wasserfall engine testing finally led to success with the injector plate and a single combustion-chamber motor. The equivalent A4 engine redesign was sidetracked by the urgency to get the missile into mass production.
• The 1.5 tonne thrust engines for the A3 and A5 were designed at Kummersdorf. At Peenemuende separate work was done in developing 1.4 and 4.2 tonne thrust motors to test the A4 injection system.
• Von Braun arrest was personally ordered by Himmler as revenge for Von Braun's resistance to the V-2 team being taken over by the SS
• Modification of the A4 engine was constant due to changes in available steel and other materials.
• Oberth was interrogated by Dr. Theodore von Karman as part of Project Dustbin after the war.
• The method used to transfer the Wasserfall missile from development to production - assignment of Henschel as prime contractor from the beginning of the process - was superior to the V-2 mess.
• The Allied bombing of Peenemuende of August 17, 1943 was disruptive and resulted in the loss of a few months of development and production work due to dispersion and reorganization. However other raids and the daily air raid warnings were taken in stride and were not disruptive of the work.
• The V-2 was not equipped with a range-safety destruct system. The military did not consider the danger sufficient to warrant the extra expense and complexity.
• The A9/A10 transoceanic missile idea was in fact found to be unworkable due to heat transfer issues.
• War shortages of material forced incorporation of new changes to the V-2 during production. Aluminium had to be used for the liquid oxygen tank. A paperboard tank was considered for the alcohol fuel but never put into production.
• Von Braun accepted an "honorary" rank and subsequent promotions in the SS. He purportedly consulted with others in the rocket development group, deciding that his SS membership would be valuable in protecting the project.
• Von Braun's management style stressed the responsibility of individuals, not committees. He was able to talk to everybody at every level. But often his practice of going around intervening management levels and giving orders to someone else's subordinates caused friction
• The working environment at Peenemuende was contrary to normal rules of military life. Although enlisted men were often supervising officers, it worked.
• The Peenemuende engineers had very little direct contact with the regular Army officers, even socially.
• More V-2 missiles were fired at Allied dock facilities at Antwerp than at London
• Oberth was inspired to study how man could reach space during the apparition of Halley's Comet in 1910.
• Von Braun was heard to say that it would have been preferable to develop rocketry for space travel rather than war. But if it was necessary to develop a war rocket to reach space, he was willing to do so. Dornberger ordered von Braun not to mention space in Hitler's presence.
• Discussion of spaceflight at Peenemuende was only done privately. Such discussions were risky and could only take place within a small, selected group of people.
• A key issue in obtaining missile accuracy was monitoring lateral dispersion of the missile due to wind during ascent. Technical approaches included a radio guide beam or accelerometers to measure lateral motion. Both the accelerometer and radio cut-off systems were used in the field, but the radio system was superior in accuracy. It was found that a three-axis platform was needed to make the lateral accelerometer work, and there were big delays in getting a platform system developed.
• The thrust and planned dimensions of the A10 transatlantic rocket first stage were used to determine the size of the research and production shops and test stands at Peenemuende.
• The V-2 engineers often held "parties with rocket fuel" using the ethyl alcohol delivered as propellant for the rocket. In common with later rocketry projects, the engineers were under tremendous strain and worked very hard but remained enthusiastic.
• As opposed to the rocket diehards, for most people at Peenemuende the working environment was "nothing special".
• The development of the V-2 guidance system evolved as follows:
  • The A3 system
  • The Sg 52 platform and control system developed for the A5 in 1938-39 This was a stable control system based on rate gyros, but was found not to be an ideal solution
  • The Sg 64 improved system developed for the A5 and tested in launches
  • The Sg 66 developed by Kreiselgeraete in 1940-42 for the A4. This electromechanical control system used unbalanced gyro accelerometers and a 'Mischgeraet' (mixing device) to combine inputs, thereby eliminating the need for rate gyros. However Kreiselgeraete was only experienced in naval equipment, and applying the principle to rocket guidance was completely foreign to them. Neverthelss, since Kreiselgeraete was a small company, they could respond with flexibility and speed to the rocket team's requests.

    Siemens developed an alternate system based on two gyros to determine attitude and follow a fixed-plane pitch program. The Siemens system was favored up to mid-1942 due to its production simplicity. Siemens also had a greater manufacturing and technical capacity. But its large size made it unresponsive to the rapid pace of development. A surplus Siemens guidance system, or an American copy, was used for the Explorer I launch in 1958.

    A third system by Askania-Moeller was briefly put into development, but quickly abandoned.

  • The Kreiselgeraete Sg 70 platform was designed as a replacement for the Sg 66 to eliminate aluminum gimbals in 1944-1945. Kreiselgeraete's development labs were evacuated to Sudetenland in 1943 after air raids in Berlin, impacting development after that date.
• The basic A4/A5 aerodynamic configuration was based on the shape of the Wehrmacht "S" model bullet. Refinements were made by trial and error tests in Hermann and Wieselsberger's wind tunnel at Aachen.
• One of von Braun's unique contributions was emphasizing horizontal communication between groups to solve problems. He was the primary initiator of this management concept.
• Von Braun was a late-riser.
• The Peenemuende engineers were poorly prepared for the conversion from laboratory development to production of the A4. Over 65,000 changes were made to the missile.
• Klaus Riedel was not effective as head of test stand work. Thereafter Von Braun assigned him to development of the mobile launch system for A4, where he was very successful.
• Regener was interested in use of the V-2 for scientific research in the ultraviolet and cosmic ray portions of the electromagnetic spectrum. Meetings were held in Friedrichshafen in 1943 to discuss the "Regener Tonne" (Regener one-ton scientific payload). Groettrup was highly involved in this project.
• Kammler wanted to launch test V-2's from Heidelager and Heidekraut against Polish towns behind the Russian lines, but the Army blocked the move.
• The in-house research-and-development philosophy of the Von Braun team resulted in problems in getting manufacturers for production. Materials problems made it difficult to get good production quality from contractors.

Manufacturer: Von Braun. Launches: 4300. Success Rate: 78.00%. First Launch Date: 1942-06-13. Last Launch Date: 1952-09-19. Launch data is: incomplete. Apogee: 200 km (120 mi). Liftoff Thrust: 264.900 kN (59,552 lbf). Total Mass: 12,805 kg (28,230 lb). Core Diameter: 1.65 m (5.41 ft). Total Length: 14.00 m (45.00 ft). Development Cost $: 2,000.000 million. in: 1943 average dollars. Total Production Built: 5789. Flyaway Unit Cost $: 0.018 million. in: 1944 unit dollars.

German production version.

Apogee: 85 km (52 mi). Liftoff Thrust: 270.000 kN (60,690 lbf). Total Mass: 12,800 kg (28,200 lb). Core Diameter: 1.65 m (5.41 ft). Total Length: 13.60 m (44.60 ft).

Pioneering US demonstration of a two stage launch vehicle, coupling a V-2 with a WAC Corporal. The first ballistic missile fired from Cape Canaveral.

In February 1946 Malina at the Jet Propulsion Laboratory calculated that a V-2 with a Wac Corporal second stage could achieve Mach 9. The WAC was equipped with canted fins with 50% more area than the ground-launch design to impart the necessary stability from the high-altitude release top the V-2. However the first tests showed the fins were ineffective, and spin rockets were added. Rails were fitted in the V-2's nose into which the Wac Corporal's fins slotted.

Historical Essay © Andreas Parsch

General Electric RTV-G-4/RV-A-4 Bumper

In February 1946, the JPL (Jet Propulsion Laboratory) started to study the possibility of a two-stage research missile consisting of a V-2 (A-4) first stage and a WAC Corporal as the second stage. In October that year, the U.S. Army agreed to fund this project as the Bumper, and assigned overall responsibility to General Electric's Hermes program (for the latter, see page on SSM-A-16 Hermes A-3B). The Bumper would serve two primary purposes. First, it would be the first two-stage liquid-fueled rocket ever built, and as such would explore problems related to stage separation and rocket ignition at high altitude. Second, it would greatly increase the maximum altitude reachable by a small research rocket.

Except for the nose cone, which had to be altered to connect to the WAC Corporal, the V-2 was essentially unchanged. The WAC, however, had to be a bit more extensively modified, leading to the configuration called Bumper Wac. Because it had to fly stable in the thin atmosphere above 40 km (25 miles), the Bumper Wac had four large fins in place of the WAC Corporal's three smaller ones, and additionally had two small solid-fueled spin motors to induce a gyro-stabilizing spin for exo-atmospheric flight. It was carried on the V-2 with its fins recessed into the V-2's nose cone. The staging mechanism worked by reducing the V-2 engine's thrust at a predetermined speed, followed by a signal to the Bumper Wac to ignite its engine. The latter then burned through a wire, thereby signalling V-2 engine cutoff. With the V-2 decelerating, the upper stage could slide out of its rails and begin its free flight.

In February 1948, the designation RTV-G-4 was assigned to the Bumper, and in May that year the first Bumper was launched. It had only a dummy upper stage with a small solid-propellant charge to test stage separation, and did achieve its objectives. The first flight with a live Bumper Wac (the third one) occurred on 30 September 1948, but failed because the Wac's engine exploded on ignition. A design deficiency was tracked down and corrected, and (after a V-2 failure in November), the fifth Bumper flight on 24 February 1949 was the first full success. In that day, the upper stage reached an altitude of 393 km (244 miles), which was a new record for any man-made object. This record would hold several years.

After a V-2 failure on the sixth flight, it was decided that the remaining two Bumpers would be used to fly the Bumper Wac as fast as possible to produce aerodynamic data at unprecedented speeds. For this purpose, the V-2 would fly an arched trajectory and release the Bumper Wac in almost horizontal attitude. These tests needed a firing range with a large open unpopulated area (like the open sea), and the Army selected the area of Cape Canaveral in Florida. Thus the Bumper project became the "founding father" for the world's most famous space launch facility. On the first launch of an RTV-G-4 at the Cape, the upper stage failed to ignite, but the second and final attempt on 29 July 1950 (Bumper flight 8, but actually vehicle #7) was successful and the Bumper Wac reached a speed of 5260 km/h (3270 mph).

In mid-1951, the Bumper's official designation was changed from RTV-G-4 to RV-A-4, although the program was no longer active by then.

Note: Data given by several sources show slight variations. Figures given below may therefore be inaccurate!

Data for RTV-G-4:

[1] Peter Alway: "Rockets of the World", Saturn Press, 1999
[2] Frederick I. Ordway III, Ronald C. Wakeford: "International Missile and Spacecraft Guide", McGraw-Hill, 1960

Manufacturer: General Electric. Apogee: 250 km (150 mi). Liftoff Thrust: 267.000 kN (60,023 lbf). Total Mass: 12,862 kg (28,355 lb). Core Diameter: 1.65 m (5.42 ft). Total Length: 17.25 m (56.61 ft). Span: 3.56 m (11.69 ft).

• Stage Number: 1. 1 x Stage: A-4. Gross Mass: 12,805 kg (28,230 lb). Empty Mass: 4,008 kg (8,836 lb). Thrust (vac): 311.800 kN (70,095 lbf). Isp: 239 sec. Burn time: 68 sec. Isp(sl): 203 sec. Diameter: 1.65 m (5.41 ft). Span: 3.56 m (11.67 ft). Length: 12.00 m (39.00 ft). Propellants: Lox/Alcohol. No Engines: 1. Engine: A-4. Other designations: V-2.

• McDowell, Jonathan, Jonathan's Space Home Page, Harvard University, 1997-present. Jonathan McDowell's complete on-line listing of all objects orbited and over 20,000 rocket launches Accessed at: http://www.planet4589.org/jsr.html.

• Emme, Eugene M, Aeronautics and Astronautics: An American Chronology of Science and Technology in the Exploration of Space 1915-1960, NASA, 1961. Accessed at: http://www.hq.nasa.gov/office/pao/History/timeline.html.

• Ley, Willy, Rockets Missiles and Men in Space, Viking Press, New York, 1968. ISBN: 0670602264. Willy Ley was one of the great science writers and promoters of spaceflight in the 1950's. This book covers basic concepts and the history of rocketry up to the early 1960's. More at amazon.com...

• Vetrov, G S, S. P. Korolev i evo delo, Nauka, Moscow, 1998. ISBN: 5020036846. The collected papers of Soviet Chief Designer Korolev. A tremendous source of new information and insight on the Soviet space program. Russian language. More at amazon.com...

• Siddiqi, Asif A, Soviet Space Web Page, 1999 via Dietrich Haeseler. Asif Siddiqi presents material that could not be fit into his monumental 'Challenge to Apollo'. Accessed at: http://home.earthlink.net/~cliched/main_space.html.

• Alway, Peter, Rockets of the World, Saturn Press, Ann Arbor, 1995. ISBN: 0962787655. Comprehensive account of world rocketry, from the beginning 'til now, from sounding rockets to Saturns. Oriented toward rocket modellers, with accurate drawings and color guides. More at amazon.com...

• Michels, Juergen and Przybilski, Olaf, Peenemuende und seine Erben in Ost und West, Bernard & Graefe, Bonn, 1997. ISBN: 3763759603. Marvelous German language book traces the 'technology transfer' from the Peenemuende refugees to the rocketry programs of America, Russia, Germany, and other countries. More at amazon.com...

• Parsch, Andreas, DesignationSystems.Net, . Outstanding, unique reference for aircraft, missiles, propulsion, and avionics systems. Accessed at: http://www.designation-systems.net/.

• Dornberger, Walter, Peenemuende, Moewig, Berlin 1985.. ISBN: 3811843419. German-language account of the development of the V-2 by the Commander of the Peenemuende rocket development centre. More at amazon.com...

• Heinemann, Edward H, and Rausa, Rosario, Ed Heinemann: Combat Aircraft Designer, Naval Institute Press, 1980. ISBN: 0870217976. Autobiography of one of the great aircraft designers of all time, including accounts of the D-558 rocketplane series. More at amazon.com...

• V2Rocket.Com A-4/V-2 Resource Site, . Accessed at: http://www.v2rocket.com/start/start.html.

• Neufeld, Michael, The Rocket and the Reich: Peenemunde and the Coming of the Ballistic Missile Era, Harvard University Press, 1996. ISBN: 067477650X. More at amazon.com...