During the design of the A-4 ballistic missile in 1941–42, the engineers began discussions about the possible launch configurations for the weapon. From a strictly technical standpoint, a fixed site was preferred for many reasons. To begin with, the A-4 missile was extremely complicated, requiring a substantial amount of test equipment to monitor the missile subsystems prior to launch. In addition, the A-4 used liquid oxygen (LOX) as the oxidizer for its fuel, and this chemical had to be maintained at super-cold temperatures using elaborate refrigeration and insulation techniques that were easier to undertake at a fixed site than at a mobile field site. Indeed, the liquid oxygen oxidizer, codenamed A-stoff by the Germans, would prove to be the main bottleneck in the combat launches of the A-4 missile. German industrial facilities produced only about 155 tons of LOX daily plus a further 60 tons in the occupied countries. Although the fueling operation for an A-4 missile consumed about 4.7 tons, on average it took about 15 tons per missile launch as about 5 tons of LOX boiled off during transit from the factory to the field. This implied that all of Europe produced only enough LOX to launch an average of 14 A-4 missiles daily with the assumption that all the LOX was available to the missile program, which of course was not the case due to industry and military requirements. One solution was to substantially increase the production capacity for LOX, but there would still be a considerable amount of wastage shipping the LOX from plants to the missile units. Using fixed missile sites with their own LOX plants would substantially reduce LOX wastage and increase the daily number of missile launches possible.
Although a fixed site would be more efficient, the missile would have to be launched from locations well within the range of Allied medium bombers, and so any fixed site was likely to be heavily bombed. Such a site could be fortified, but this would add to the expense of the program. Two different bunker designs were prepared in 1942 including sketches and architectural models. The B.III-2a design envisioned erecting the missile inside the bunker and then towing the launch pad outside the bunker for launch; the B.III-2b design had two openings in the roof which would permit the missiles to be elevated from within the protective confines of the bunker and launched from the roof.
The Walter catapult for the FZG-76 was eventually configured as a modular unit to make it easier to assemble in the field. This is a partial launcher preserved at the Eperlecques Museum near the Watten Bunker, which can be seen in the background. This launcher is missing the distinctive blast deflector found at the end of the catapult. (Author’s collection)
In the mobile batteries, the A-4 missile was towed to the launch site on a Meillerwagen, which erected the missile on the launch pad prior to fueling. (MHI)
The alternative to fixed basing was mobile basing. This would require a mobile erector system to place the missile vertically on its launch pad, and it would require that all the elaborate testing and fueling equipment be re-packaged to fit on either railway cars or trucks and trailers to accompany the launcher into the field. While this launch configuration would be less vulnerable to air attack than a fixed site, it would be far less efficient and the rate of fire considerably less.
The head of the A-4 program, Oberst Walter Dornberger, laid out the various launch options in a study completed in March 1942. The study suggested that fixed sites could be created similar to the U-boat bunkers being built on the French Atlantic coast that would be impervious to aerial attack. However, army artillery officers favored a mobile basing system, as they were not convinced that any structure could withstand repeated air attacks and still remain functional. The issue wasn’t simply the bunker itself, but the roads and railroad lines leading to the bunker, which would be needed to provide a supply of missiles and fuel. Although a final decision was put in abeyance until the A-4 missile proved viable, initial design work began on a mobile missile launcher in early 1942 including both road-mobile and rail-mobile options. Some more exotic launch options were considered, including a submersible launch barge that could be towed behind a U-boat. None of these progressed beyond paper designs.
Trials of air-launched FZG-76 cruise missiles took place in 1943, with the He-111H medium bomber finally selected as the most suitable carrier. This is one of the test launches at Peenemünde; the operational aircraft launched the FZG-76 from under the starboard wing. (NARA)
The problem posed by the need for liquid oxygen for the A-4 led to the first construction effort connected with the V-weapons. In October 1942, a technical mission was sent to northern France and Belgium to inspect potential locations for the creation of two plants capable of producing 1,500 tons of liquid oxygen per month. The sites selected were Tilleur near Liège in Belgium, codenamed WL; and Stenay in the French Ardennes, codenamed WS.
The first successful launch of an A-4 Feuerteufel (fire-devil) missile from the Peenemünde test site in October 1942 led to a discussion about the program between Hitler and armaments minister Albert Speer on November 22, 1942. Hitler was shown models of the proposed launch bunkers as well as details of the proposed mobile launchers. He agreed to a production plan for the missile, but made clear his preference for the bunker launch sites in addition to the Army’s preferred mobile launcher option. As a result, Speer met with Dornberger in Berlin on December 22, 1942, to lay out the program in more detail. Speer instructed that the bunkers be designed to the special fortification standard (Sonderbaustärke) with a 5m-thick steel-reinforced concrete ceiling and 3.5m-thick walls. Each bunker would contain enough missiles for three days of launches, totaling 108 missiles, along with sufficient fuel and liquid oxygen. Each bunker would be manned by 250 troops. Construction of the first bunker somewhere in the Boulogne area would begin as soon as possible and would be followed at the end of June 1943 with a second bunker on the Cotentin Peninsula in France opposite southern England. The Organization Todt (OT), the paramilitary construction group that had come under Speer’s control following the death of Fritz Todt in an airplane accident in February 1942, would undertake construction. Supervision of the missile construction program was undertaken by director-general of OT, Xaver Dorsch, due to the high priority afforded the program by Hitler.
An experimental railroad launch system for the A-4 missile was developed and tested in 1944, but its use was rejected due to the vulnerability of the European railway network to Allied air attack. The Red Army later captured this equipment and used it in the late 1940s in its early ballistic missile program. (NARA)
The Walter catapult was operated by a gas-generator cart at its end, which generated a powerful pulse by combining T-stoff (hydrogen peroxide) and Z-stoff (sodium permanganate) fuel. This was fed into a tube running through the catapult rail, propelling a piston, seen in the foreground, which was attached underneath the FZG-76 missile. The Imperial War Museum, Duxford, has the only complete V-1 launch system including a full Walter catapult and the associated equipment. (Author’s collection)
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KRAFTWERK NORDWEST, WATTEN (EPERLECQUES), FRANCE |
This was the first large launch bunker built for the army’s A-4 ballistic missiles and it is shown here in its planned configuration. Design of the bunker was headed by Werner Flos, chief engineer in the offices of Organization Todt-Zentrale in Berlin. This launch bunker was a further evolution from the B III design shown to Hitler in 1942. The most significant change was a decision in March 1943 to shift a planned liquid oxygen plant and its five compressors from Stenay to this bunker, leading to its enlargement. Codenamed Kraftwerk Nordwest (KNW: North-west Electrical Works), it was located near the Eperlecques woods, though the Germans usually called it the Watten Bunker due to its proximity to the nearest railroad station.
The design incorporated three principal elements: a railroad station, a missile assembly and preparation vault and the liquid oxygen plant. The north side of the bunker contained a major railroad station below it with a protected tunnel coming in underground on the west side through a fortified tunnel that connected to the main Calais–St. Omer line to the east of the site via a spur-line. The plan was to ship standardized trains to the KNW consisting of 20 R wagons; 10 X wagons and one personnel car. The R wagons each contained a single A-4 missile minus its “Elefant” warhead while the X wagons carried two Elefants each plus other associated missile components. On arriving at the KNW, the missiles were erected inside the vaults on the north side of the building and their warheads fitted. They were placed on a rail-mounted launch pad, fueled, and then moved in a fueled and erected state out of one of two armored doors on the south side of the building to a launch plaza. The walls of the exit tunnels were constructed in a chicane pattern to reduce the shock wave from the rocket exhaust during the missile launch, as there were no doors on the exterior exit. A large command tower was located in the center of the south side of the building where the launch operation was supervised. The north side of the building contained the liquid oxygen factory along with its five Heylandt compressors located in five vaults. These had the capacity to produce 50 tons of liquid oxygen per day, about enough for 20 missile launches. The bunker also had insulated storage tanks for liquid oxygen with supplies adequate for three days of launch operations. The original plan called for completion by December 31, 1943, in order to start missile launches against London by the end of the year. The building was roughly 92m wide and 28m high (300 × 90ft) requiring about 120,000m3 of concrete, roughly equivalent to that of 435 London Hilton hotels.
Allied intelligence became aware of the site in the summer of 1943 and, after consultation with civil engineers, decided to attack it after the first major pouring of concrete but before the concrete had the time to fully harden. The first major raid was conducted by 224 B-17 bombers of the US Eighth Air Force on the afternoon of August 27, 1943, delivering 366 tons of bombs of which 327 landed on the site, mainly the north side. Four more raids were conducted from August 30 to September 7, substantially destroying the north side of the building. The damage was so great that the Wehrmacht had to abandon use of the site for V-2 launches and instead salvaged what they could be completing parts of the south side of the building as an oxygen manufacturing plant dubbed Betonklotz (concrete block) to support missile operations. During early 1944, three oxygen compressors were installed at the site. After the start of Operation Eisbär, the remainder of the bunker was attacked by the RAF using Tallboy bombs, one of which penetrated the building and put an end to any further construction.
The enormous internal volume of the Kraftwerk Nordwest at Watten is evident from this photo inside one of its cavernous halls. The painting on the wall depicts a full-sized V-2 missile. (Author’s collection)
The survey of potential launch sites began in the final days of December 1942. The team concentrated on sites in the Artois region of France and finally settled on a site near the town of Watten, since the area was easily accessible by rail and canal, there was a good local electrical power-grid, and there were several forested sites that appeared suitable for construction while at the same time being remote enough to prevent the local French villagers from observing the work. The first bunker was given the cover-name KNW (Kraftwerk Nordwest: Northwest Electrical Works). Initial plans were completed on February 12, 1943, and it was decided to merge the planned Stenay Oxygen Plant within the KNW Bunker. This meant enlarging the bunker considerably beyond that envisioned in the preliminary studies, requiring some 120,000m3 of concrete and about 360,000 tons of material during the four months of construction. Besides the bunker itself, the plan included a substantial upgrade to the neighboring railroad lines to permit resupply once the missile campaign began, and also included preliminary efforts to create supporting sites for stocking missiles and other necessary supplies. The nearby town of Wizernes was selected as the location for the main supply base, codenamed SNW (Schotterwerk Nordwest: Northwest Gravel Works). A limestone quarry in the town was selected since it would permit extensive tunnels to be dug for sheltering the missiles prior to delivery to the launch bunker. Hitler approved the plan on March 29, 1943, with the KNW Bunker scheduled to be ready for combat by December 31, 1943.
This is the model of the B.III-2b bunker design shown to Hitler in November 1942, which initiated the A-4 bunker program. This version erected the missile inside the bunker then used an elevator to move the launch pad outside for launch. It was smaller than the eventual Watten Bunker, lacking a liquid oxygen plant. (MHI)
The second V-weapon to receive approval for construction was the HDP pump gun. Due to its enormous length of 127m, the gun could not be made mobile and it would inevitably have to be deployed from a fixed site with the tube inclined at a set angle. The most obvious solution was to place it in some form of underground fortification, whether natural or man-made. The task of finding a launch site was handed to Major Bock of Festung Pioneer-Stab 27, the fortification regiment of LVII Corps, Fifteenth Army, based in the Dieppe area. A study in early 1943 concluded that a suitable hill with a rock core would be ideal as the gun tubes could be placed in drifts (inclined tunnels) and the support equipment and supplies located in tunnels adjacent to the firing tunnels. A site was selected at a limestone hill near Mimoyecques on the Pas-de-Calais. Codenamed Wiese (meadow) and Bauvorhaben 711 (construction project 711), initial construction work for support tunnels began in late May 1943 even though the gun concept had not yet been fully proven by full-scale tests. The initial configuration consisted of two gun complexes, each with five drifts 130m long, which could each accommodate five HDP barrels for a total of 50 guns. The work attracted the attention of the Royal Air Force (RAF) and three air raids were conducted against the site in early November 1943. In the wake of the air attacks, the Army decided to scale back the project by halting work on the western battery before any shafts were created, and concentrating on the eastern battery. The plans were to have the first cluster of five tubes ready by March 1944, and the full complex with 25 tubes by October 1, 1944. A full-scale trial at the Misdroy proving ground in April 1944 led to a failure after only 25 rounds had been fired. These problems led to a further reduction in the scope of the eastern battery at the Wiese site from five drifts to three although work had already begun on some of the other drifts. Later tests in late May 1944 achieved a range of 90km, insufficient to reach London, but at least proving the feasibility of the concept. Artillerie Abteilung 705 was organized in January 1944 under Oberstleutnant Georg Borttscheller to operate the Wiese gun complex.
This shows a test version of the Tausenfüßler HDP supergun at the Wehrmacht’s Hillersleben artillery test range after its capture in 1945. (MHI)
The Wiese Bunker at Mimoyecques has been converted into a museum, and a replica of a single Tausenfüßler has been created in one of the actual gun chambers. In reality, five guns were ganged together vertically in each drift. (Author’s collection)
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WIESE B711, MIMOYECQUES, FRANCE |
The site for the Tausenfüßler supergun was constructed in a limestone hill about 5km north of the Hidrequent lime quarries, and codenamed Wiese (meadow) and Bauvorhaben 711 (B711: construction project 711). Work began in September 1943 by constructing rail lines to support the construction. Shafts were dug starting in October, which prompted two Allied air attacks on November 5 and 8 that delayed work for about a month. The original configuration of the site was for two tunnel complexes with a total of 50 gun tubes, but after the air raid, the western shaft was abandoned after little work had been completed. The remaining eastern complex consisted of five drifts angled at 50 degrees to the horizontal reaching 105m (340ft) below the hilltop. The five drifts exited the hilltop through a concrete slab 30m wide and 5.5m thick (100 × 18ft). Large steel plates protected the five openings and each port had a special armored door. The internal tunneling and elevator shafts were quite extensive to support the guns during operation, and had the site become operational, about 1,000 troops of Artillerie Abteilung 705 and other supporting units would have been deployed at Mimoyecques.
The HDP Tausenfüßler 15cm supergun was 127m (415ft) long. The distance from the breech to the first propellant charge was 6m, and then 3.2m for subsequent chambers. Each of the five drifts contained a stacked cluster of five gun tubes for a total of 25 gun tubes planned for the site. By the summer of 1944, only three of the five drifts had been completed.
Although there were a dozen attacks prior to D-Day, these were largely ineffective due to the durable configuration of the site. This changed on July 6, 1944, when the RAF struck again with 16 Lancasters carrying 6-ton Tallboy bombs. One Tallboy directly impacted the concrete slab on top of the complex, collapsing Drift IV. Three other Tallboy bombs penetrated the tunnel system below, creating extensive damage. Some effort was made to clean up the debris, but by late July it was obvious that the damage was too severe to justify continuation of the construction, especially since the RAF could very well stage additional Tallboy raids. Plans were made to reconstruct the Tausenfüßler gun battery at the Rixtent B81 liquid oxygen facility, but this never transpired. Although not formally abandoned, the Canadian 3rd Infantry Division overran the Mimoyecques site on September 5, 1944.
The Tausenfüßler fired the 15cm Sprenggranate 4481 projectile that weighed 97kg at the time of launch, seen here during technical evaluation at Aberdeen Proving Ground in Maryland after the war. (MHI)
Unlike a conventional cannon, the HDP supergun used multiple propellant chambers angled off the main chamber that were electrically detonated in sequence to propel the projectile. This is a test example at the Hillersleben proving ground. (MHI)
The FZG-76 cruise missile was the last of the V-weapons to receive deployment approval. The launch system for the missile was determined by the engine choice, a simple pulse-jet engine. Unlike gas-turbine jet engines, which can operate from a cold start, a pulse-jet engine requires a strong air-flow through the exhaust chamber before the engine can operate. The only way to accomplish this is to launch the missile using a secondary propulsion system, at which point the pulse-jet can be ignited. Fieseler looked at a variety of launch approaches for the FZG-76, usually based on long rail launchers since this provided sufficient time for the pulse-jet to ignite. The first approach was a Rheinmetall-Borsig rocket sled mounted behind the missile, but after trials this was rejected in favor of a steam catapult design from Hellmuth Walter Werke (HWW) called the WR 2.3 Schlitzrohrschleuder (split-tube catapult). A small gas generator trailer was attached to the base of the launch rail which mixed a combination of T-stoff (hydrogen peroxide) and Z-stoff (sodium permanganate) to create high-pressure steam that was pumped into a tube inside the launch rail box propelling a piston, connected underneath the missile. This system was somewhat similar to the steam catapults used on aircraft carriers except for the method of generating the steam. The Walter catapult was attractive since it provided more than enough power to get the missile airborne, and also was cheap to operate since it was reusable. On the negative side, it required the use of a very long 49m (160ft) launch rail, which was cumbersome to deploy. In the rush to deploy the FZG-76, other alternatives such as zero-launch solid rocket boosters were not seriously explored. The awkward launch rail would prove to be the Achilles heel of the V-1 missile system.
As was the case with the Army, so too was there a strenuous debate within the Luftwaffe over fixed versus mobile basing. The Luftwaffe’s Flak arm was assigned responsibility for the launch sites, and the Flak commander, General der Luftwaffe Walther von Axthelm, wanted the missiles deployed in a large number of small “light” launch sites that could be easily camouflaged. However, the head of the Luftwaffe production program, General-feldmarschall Erhard Milch, knew that Hitler favored large launch bunkers, so he argued for this approach. A compromise was finally worked out during a meeting with the head of the Luftwaffe, Hermann Göring on June 18, 1943, with a plan to create four heavy Wasserwerk (waterworks) launch bunkers along with 96 light installations.
Wasserwerk St. Pol near Siracourt was the only one of the first four waterworks to be nearly completed. This drawing from one of the wartime technical intelligence reports shows the state of the building in the summer of 1944. The precise launcher configuration has never been determined; Allied sketches show a single launch ramp as seen here but German accounts indicate that two launch rails were planned. (NARA)
The bunker at Sottevast was intended to serve as a storage facility and base for a V-2 battalion near Cherbourg. It was only partially completed when the US Army overran the site in late June 1944, as seen here. (NARA)
On the night of July 24, 1943, the RAF began Operation Gomorrah intended to destroy the city of Hamburg. The raids continued for several nights, starting a firestorm that devastated the city and left more than 50,000 dead. Hitler was infuriated, and critical of the Luftwaffe both for their failure to stop the attacks and their inability to retaliate. When Speer raised the issue of the FZG-76 missile program on July 28, 1943, Hitler enthusiastically approved the program, insisting that they be ready to pulverize London by the year’s end in concert with the A-4 ballistic missile and the Tausenfüßler supergun. The complex of secret weapons sites in the Pas-de-Calais area were collectively called the Sonderbauten: “Special Construction” by Organization Todt.
The first of the heavy bunker sites were Wasserwerk Desvres located near Lottinghen and Wasserwerk St. Pol located near Siracourt, both in the Artois region of northeastern France. Another two would follow on the Cotentin Peninsula west of Normandy, Wasserwerk Valognes near Tamerville and Wasserwerk Cherbourg at Couville to the southeast of the port; the eventual goal was ten Wasserwerke. Even though this program started several months later than the A-4 ballistic missile program, the plan was to have the four Wasserwerke operational at the end of December 1943 to start the missile campaign against London, plus four additional bunkers by March 1944. However, work on the sites was badly delayed by other priorities as Organization Todt was stretched thin by its commitments to reinforcing the Atlantic Wall for the expected Allied invasion as well as a major rebuilding effort in Germany after the RAF’s “Battle of the Ruhr” bombing campaign in the autumn of 1943.
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WASSERWERK NO. 1 ST. POL, SIRACOURT, FRANCE |
The FZG-76 cruise missile bunker design was codenamed Wasserwerk (waterworks) by the Luftwaffe and four of the initial design were started at Siracourt and Lottinghen in the Pas-de-Calais and Tamerville and Couville on the Cotentin Peninsula. Of these, only Wasserwerk St. Pol near Siracourt came anywhere near completion due to Allied bombing of the sites.
This bunker design was based on the lessons of the destruction of the Watten Bunker, and used a new construction technique called Verbunkerung, which attempted to minimize the vulnerability of the bunker during construction. The structure was about 215m long, 36m wide and 10m high (700 × 120 × 30ft), a very low and long structure compared to the earlier Watten design and requiring some 55,000m3 of steel-reinforced concrete. The precise configuration of the finished bunker remains a bit of a mystery as none was ever completed, and full architectural plans have not been found. The design was basically an elongated tunnel with railroad access at the ends for supplying the bunker. Presumably, the interior would have been used for assembling and preparing the missiles for launch as well as housing the launch battery. There is some mystery about the intended launcher configuration. The remains of the site at Siracourt suggests that a launch ramp would have emanated from the center of the building, and Allied intelligence presumed a single Walter catapult would have been fixed here. However, some German accounts have suggested that each site would have two launchers, so it is possible that the earthen launch ramp would have had two parallel launch ramps instead of only one seen here.
In spite of Allied bombing, Wasserwerk St. Pol at Siracourt continued construction until June 25, 1944, when the site was hit by 16 Lancaster bombers carrying the 6-ton Tallboy bomb. By this stage, about 90 percent of the concrete work was complete except for the sections at either end. However, the earth core had not yet been excavated from the insides of the structure. One Tallboy directly impacted the center of the roof, completely penetrating the structure, while another impacted within feet of one of the walls, causing significant damage. In total, Siracourt was subjected to 27 attacks with 5,000 tons of bombs. Even without the coup de grace of the Tallboy attack, the site was so badly torn up by the incessant bombing that it is hard to see how it ever could have been supported by rail transport.
