Eight


HITLER’S SMART BOMBS

THE FEDDEN MISSION came away from Nordhausen having seen for themselves the starkest extremes of the Nazis’ secret weapon programme. On the one hand they had witnessed the abject horror and depravity of the slave labour system, while, on the other, they could not fail to marvel at the most technologically advanced weapons programme the world had ever seen.

The following day they flew south to Munich, where they inspected the BMW engine works and billeted overnight at the American 3rd Army Intelligence Centre at Freising. On Thursday 21 June the mission divided into two groups, with four members of the team departing by road to Rosenheim and the BMW rocket development department at Bruckmühl. As chief engineer and technical director in charge of BMW’s jet, piston and rocket development, Bruno Bruckmann accompanied them, explaining that BMW’s intensive development of rockets had started in early 1944 on RLM orders. It was conducted under the control of an engineer named Szibroski, an SS man who had disappeared before the American Army arrived in April 1945.

Many of the German rocket projects had their origins in the early stages of the war, or even before it in some cases, but the impetus to wheel them out had come with the intensification of the Allied strategic bombing campaign. As we have seen, the V-1 cruise missile and the V-2 ballistic missile were dedicated offensive weapons and had no defensive role to play, but rocket-power could be used very effectively to augment the existing ground-based anti-aircraft defences of the Luftwaffe’s flak regiments, or to fill the gaps left by the increasingly overstretched fighter aircraft. In addition to their use as surface-to-air anti-aircraft missiles, the range of other applications included aircraft-launched weapons – either air-to-air against other aircraft, or air-to-surface against ground targets or shipping – and even surface-to-surface as a form of artillery. When combined with a variety of guidance systems this array of missiles became the first generation of smart bombs, although, lacking the technology to home in on a target autonomously without human guidance, it might be more accurate to describe them as semi-smart bombs.

Book title

Press photograph released in November 1944 of an HS 293 anti-shipping missile with Walter 109-507 B liquid-fuelled rocket motor.

THE BMW TYPE 109-718

As it turned out the first rocket motor the Fedden Mission was shown by Bruckmann wasn’t a weapon at all. The BMW Type 109-718 liquid-fuelled rocket – 109 was also the RLM prefix for rockets – was a small non-expendable assistor unit designed to be used in conjunction with the BMW 003 jet engine to which it was fitted at the rear end; a configuration known as the BMW 003R. The internal and external main chambers were liquid-cooled by one of the fuels, nitric acid, passing round a spiral tube inside the outer member. The whole engine unit weighed 176lb (80kg) and gave a thrust of 2,755lb (1,250kg) for three to five minutes. The fuels used were nitric acid and a mixture of hydrocarbons. Fuel consumption was 5.5kg per 1,000kg of thrust per second, and it was estimated that with two of these assistors a Messerschmitt Me 262 could climb to 30,000ft (9,150m) in three minutes.

Unlike the expendable RATO units, this was specifically intended for rapid climb or bursts of speed in an emergency. The 109-718 had the potential to turn a jet fighter into an ultra-high-speed interceptor while at the same time conserving the rocket fuel through intermittent operation, unlike the dedicated rocket-powered aircraft such as the Messerschmitt Me 163B. It was hoped that further development work would enable the unit to use standard jet fuel in due course. The fuel pumps on the 109-718 were the centrifugal type and ran at 17,000rpm, with the fuel pressure at 50 atmospheres. A special drive with universal joints was provided on the jet engine for these pumps, and ran at 3,000rpm. The fuel flow to the unit was controlled by spring-loaded valves operated by a servo motor, and a special automatic control was being developed for this purpose to prevent an inequality of thrust on twin-engine jet aircraft.

The 109-718 rocket units were tested on several prototypes including the Me 262 C-2b Heimatschützer (‘home defender’), and the single-engined Heinkel He 162E in March 1945. (The Heimatschützer was the Me 262 C-1a with a single Walter 109-509 S1 fitted in the rear fuselage and exhausting under the tail.) Bruckmann informed Fedden that twenty of the 109-718 units had been constructed, and the production time for each one was around 100 hours.

Stand-alone RATO units were frequently used by the Germans for a number of reasons, either to gain additional lift at take-off for heavily-laden aircraft, to provide extra thrust, or to save jet fuel. The Walter HWK 109-500 Starthilfe (‘take-off assistor’) was a liquid-fuelled rocket pod which could provide 1,100lb (500kg) of thrust for thirty seconds – the thrust was doubled as they were always used in symmetrical pairs. Once the fuel was exhausted the pods were jettisoned by the pilot and returned to the ground by parachute to be serviced and used again. The HWK 109-500 entered service in 1942 and around 6,000 were manufactured by Heinkel. They were used extensively on a wide range of aircraft, including the under-powered Jumo 004-engined Arado Ar 234.

Book title

At BMW’s rocket development department at Bruckmühl, Rosenheim, Bruno Bruckmann and W.J. Stern pose beside a BMW 109-558 liquid-fuelled rocket motor for the Henschel Hs 117.

SCHMETTERLING

The next rocket Fedden’s team examined at Bruckmühl was the BMW 109/558 for the Henschel Hs 117 ground-to-air guided missile. The Hs 117 was codenamed Schmetterling (‘butterfly’), although it looked more like a slender bottlenose dolphin with central sweptback wings and a cruciform tail. The nose was asymmetrical with the warhead extension on one side and a small generator propeller on the other. Designed by a Henschel team led by Professor Herbert Alois Wagner, the Hs 117 was a medium-altitude missile targeting enemy bombers flying between 6,000 and 33,000ft (1,800m to 10,000m).

The Schmetterling was launched from a modified 37mm gun-carriage with two Schmidding 109-553 solid diglycol-fuel boosters, one above and one below the main body, giving a total thrust of about 6,000lb (2,700kg) for a duration of sixty-five seconds before falling away. After take-off the BMW rocket motor provided the main power, giving the 992lb (450kg) missile a speed of between 558 to 620mph (900 to 1,000km/h) taking it up to an altitude between 20,000 and 30,000ft (9,150m). In order not to exceed the velocity at which the missile was stable, the engine’s thrust was regulated by sliding valves in the nozzle actuated by a small electric servo activated by a Mach meter. The Hs 117 was radio controlled by two operators using a telescopic sight and joystick. Once near to a target, acoustic and photoelectric sensors homed in automatically from a range of 33 to 66ft (10 to 20m), and proximity fuses detonated its lethal payload of 55lb (25kg) of explosives.

Book title

Surface-to-air weapons: V-2 (A4) rocket, Wasserfall, Bacham Natter, Rheintochter, Enzian and Feurlilie.

Book title

Hs 298 air-to-air missile, an Me 328 shown with Argus pulsejets, the Fi 103 R manned version of the V-1, an X-4, Hs 117 Schmetterling and the Fi 103 V-1.

The BMW 109-558 rocket motor took the form of a long tube slender enough to fit within the missile’s casing. It contained a compressed air tank, an SV-Stoff nitric acid tank, and a tank for the R-Stoff, a composite of hydrocarbon self-igniting propellant codenamed ‘Tonka’. The combustion chamber was cooled by the nitric acid and was about 18in (46cm) long with a diameter of 5in (12.5cm). A photograph in the Fedden Mission report shows Bruckmann and Stern standing behind a complete rocket assembly which was 8ft (2.4m) long overall. According to Fedden:

    The whole equipment weighed 352lb (160kg), took forty to sixty hours to make, and the production price was 400 to 500 Marks. 120 had been made. It was stated that successful experiments had been carried out with this equipment, and the rocket motor which was a clean workmanlike job had started production in parallel with the Henschel flying missile.

A ‘workmanlike job’ is probably what passes for high praise in engineering circles. The Hs 117 underwent fifty-nine test firings, of which more than half failed. Even so, full-scale manufacture commenced in December 1944, with an eventual target output of 3,000 a month projected for the end of 1945, but production was cancelled by February 1945. Some Hs 117s were test launched from a Heinkel He 111, and there was also to be an air-to-air variant of the missile, the Hs 117H, which looked the same but did not have the booster rockets. This would have been air-launched from a Dornier Do 217, Junkers Ju 88 or Ju 388, but it never made it into operation.

WASSERFALL

Wasserfall (‘waterfall’) was a higher-altitude missile than Schmetterling, and it was also much more complex and expensive to build as it was, in essence, a scaled-down version of the A4 (V-2) liquid-fuelled rocket. As an anti-aircraft missile it required a far smaller payload and range/duration than the V-2, and consequently it was only 25ft 9in (7.85m) long and weighed 8,160lb (3,700kg); roughly half the size of an A4. In appearance Wasserfall resembled the V-2, with the same streamlined bullet shape for the body, but with four short wings or fins on the midsection to provide additional control. The fins on the tail also had control surfaces, and steering was supplemented by rudder flaps within the rocket exhaust.

Unlike the V-2, Wasserfall was designed to stand for several months at a time and be ready to be fired at short notice, something for which the V-2’s highly volatile liquid-oxygen fuel was not suited. Instead the new rocket motor for the smaller missile, developed by Dr Walter Thiel, was based on Visol (vinyl isobutyl ether) and SV-Stoff fuel. This mixture was forced into the combustion chamber by pressure and spontaneously combusted on contact. Guidance was by radio control, although for night-time operations a system known as Rheinland was developed, incorporating a radar for tracking and a transponder for location which would be read by radio direction finder on the ground. An alternative system using radar beams was also under development. Because of concerns about accuracy, Wasserfall’s original 220lb (100kg) warhead was replaced by a far bigger 517lb (235kg) of explosives. Instead of hitting a single aircraft directly, the idea was that the warhead would detonate in the middle of a bomber formation and the blast effect would bring down several aircraft in one go. The missile itself was designed to break up to ensure that only small pieces fell on to friendly territory below.

Book title

The Fritz-X was a glider-bomb designed to pierce the armoured plating on Allied ships. (JC)

Book title

Another view of a captured Hs 293 anti-shipping bomb. (USAF)

Wasserfall was developed and tested at Peenemünde and in total thirty-five test launches had been completed by the time this facility was evacuated in February 1945. Subsequently the resources and manpower needed for the development of the defensive Wasserfall programme was diverted to the higher priority and offensive A4. It would appear that Hitler’s quest for taking vengeance on his enemies, whether symbolic or real, overrode the need to defend the German homeland. Production of the Wasserfall had been scheduled to begin at a huge underground factory at Bleicherode in October 1945, by which time, of course, it was already too late.

Book title

The air-launched Hs 298 radio-controlled rocket-powered missile never entered full production and the project was abandoned in January 1945.

Book title

X-4 wire-guided air-to-air missile. Pods on two wing-tips contained spools for the control wires. (USAF)

THE RHEINTOCHTER AND ENZIAN HIGH-ALTITUDE MISSILES

In parallel to Schmetterling and Wasserfall, several other anti-aircraft missiles were also in development, in particular the Rheintochter and Enzian high-altitude missiles. Rheintochter, named after Richard Wagner’s Rhine Maidens, was a multi-stage solid-fuel surface-to-air missile developed by Rheinmetall-Borsig for the German Army. Working from the top down it had four small paddle-like control surfaces near the nose for steering, plus six sweptback fins at the end of the first stage and a further four at the rear of the second, booster stage. It was 20ft 8in (6.3m) long overall including the booster stage, and the body had a diameter of 1ft 9.25in (54cm). Unusually the exhaust from the main sustainer motor was vented through six ‘venturi’ (small tubes) positioned one between each main fin. This was partly for additional stabilisation in flight, but also because the 300lb (136kg) warhead was situated behind the motor and would be attached before launch. The Rheintochter R-I was launched from a ramp or from a converted gun mounting. Guidance was via a joystick, radio control and line of sight observation.

After eighty-two test launches, further development of the Rheintochter R-I, and the proposed operational version R-II, was abandoned in December 1944 because it was only attaining the same altitude as the other missile systems. A third version of the Rheintochter, the R-III, was to have been a far sleeker affair with a liquid-propellant rocket motor for the main stage, and it did away with the second stage in favour of solid-fuelled boosters mounted to the side of the missile. Only six test firings were made.

Book title

Rheintochter III two-stage anti-aircraft missile. (NARA)

TAIFUN

Taifun (‘typhoon’) was one of the smallest of the unguided anti-aircraft rockets. Its design was instigated by Sheufen, an officer at Peenemünde, who wanted to produce a back-up or alternative to the more complicated missiles. Further developed by the Elektromechanische Werke in Karlshagen, the Taifun was an unguided missile, 6ft 4in (1.93m) long and 4in (10cm) in diameter with four small stabilizing fins at its base. The simple rocket was fuelled by a hypergolic mixture of nitric acid and Optolin – a mix of aromatic amines, gasoline, Visol and catechol – pressure-fed into the combustion chamber. Burnout occurred after two and a half seconds, by which time the rocket was travelling at 2,237mph (3,600km/h) up to a maximum altitude of 39,370ft (12,000m). The rockets would have been fired in salvoes of up to thirty at a time from a rocket launcher mounted on an adapted gun mounting. Delays in the development of the rocket motor meant that Taifun was never deployed operationally. However, if this unsophisticated and unguided weapon had been ready earlier it could have caused devastation among the Allied bombers.

BMW 109-548

Schmetterling, Wasserfall, Rheintochter and Taifun were not the only surface-to-air or anti-aircraft missiles under development in Germany. Others included the Rheinmetall-Borsig Feuerlilie F-25/F-55 which Fedden had come across at Völkenrode, and also the Messerschmitt Enzian E-4 which, because of its antecedence in the Me 163 rocket aircraft, is covered in the following chapter. The third type of rocket motor shown to the Fedden Mission at the BMW works in Bruckmühl was the BMW 109-548 used on the Ruhrstahl X-4. Described by Fedden as an ‘inter-aircraft rocket’ – they were still finding the vocabulary for all this new weaponry in 1945 – the X-4 was a formidable wire-guided air-to-air missile suitable for use with the fast jets such as the Messerschmitt Me 262.

Developed by Dr Max Kramer at Ruhrstahl, the X-4 was designed to operate from a distance outside the range of an enemy bomber’s guns. In flight the missile was stabilised by spinning slowly about its axis, at about 60rpm, thus ironing out any asymmetry in thrust. A joystick in the launch aircraft’s cockpit sent control signals via two wires feeding out from spools or bobbins located within the pods at the end of two opposing wings, and small spoilers on the tail steered the X-4. The wire-guidance system was a means of circumventing the possibility of radio signals being jammed. The range for attack was 0.93 to 2.17 miles (1.5 to 3.5km) and the total payout of the wires was around 3.5 miles (5.5km). According to Fedden the compact 109-548 rocket propelled the X-4 at 620mph (1,000km/h) and had an endurance of up to twenty seconds. The X-4 was 6ft 7in (2m) long and had a wingspan of almost 2ft 3in (73cm) with four midsection fins swept at 45°.

Carrying a 45lb (20kg) fragmentation device in the warhead, the X-4 had a lethal range of about 25ft (8m) and positioning it accurately proved very difficult to judge for the controller. Accordingly a type of acoustically triggered proximity fuse known as a Kranich was also fitted, and this was sensitive to the Doppler shift in engine/propeller sound as it approach and began to pass the enemy bombers. Flight testing commenced in August 1944, initially wing-mounted on a Focke-Wulf Fw 190, but later on the Junkers Ju 88. The X-4 had been intended for single-seat fighters such as Messerschmitt’s jet-engined Me 262, or possibly the Dornier Do 335, but the impracticality of the pilot managing to simultaneously fly the aircraft and control the missile were too great. Production of the airframe began in early 1945. This was designed to be assembled by unskilled labour, in other words forced labour, and incorporated low-cost materials such as plywood for the main fins. It is claimed that 1,000 were readied, but the Allied raids on BMW’s production facility in Stargard held up delivery of the vital 109-548 rocket motors. Consequently the X-4 was never officially delivered to the Luftwaffe. A smaller version of the X-4, the X-7, was designed as an anti-tank missile, but there is no evidence of this ever being used.

‘WINGED TORPEDOES’

The other main application of air-to-surface guided weaponry was against Allied shipping. A guided air-launched weapon greatly increased the potential range and accuracy of an attack in comparison with a direct attack using conventional bombs or torpedoes, especially on heavily guarded vessels such as warships. The Blohm & Voss company developed a series of ‘winged torpedoes’ or glider bombs, such as the Bv 143 which featured a pair of straight wings and a cruciform tail with guidance along a fixed course provided by an internal gyroscopic system. A feeler arm extending beneath the main body acted as a gauge, keeping the missile on a level glide just above the surface of the sea by activating a booster rocket within the fuselage. Four Bv 143s were constructed and tested in 1943, but the project was shelved until a more reliable automatic altimeter could be devised.

The Bv 246 Hagelkorn (‘hailstone’) was an un-powered glider bomber which did enter limited production in late 1943. Once released both of these glider bombs lacked external guidance input to ensure they hit their targets.

The most successful of the anti-shipping missiles were the fully guided Fritz X and the Henschel 293. The Fritz X was officially designated as the FX 1400, although confusingly it was also known as the Ruhrstahl SD 1400 X, the Kramer X-1 and the PC 1400X. Derived from the high-explosive thick-walled 3,080lb (1,400kg) SD 1400 Splitterbombe Dickwandig (‘fragmentation bomb’), the Fritz X had a more aerodynamic nose, four midsection stub wings and a box tail at the rear housing the spoilers or control surfaces. Engineer Max Kramer had begun development work on the missile before the war, fitting radio-controlled spoilers to free-falling 550lb (250kg) bombs, and in 1940 the Ruhstahl company became involved because of their experience in the development and production of conventional unguided bombs.

Fritz X did not have a rocket motor and upon release it glided all the way to the target, guided visually from the launch aircraft via radio-control inputs from a joystick. The missile was designed specifically to be armour-piercing, up to 5.1in (130mm) thick, and the main targets were heavy cruisers or battleships. There was a micro delay in the fuse to ensure it detonated inside the target and not immediately upon impact. Minimum release height was 13,000ft (4,000m), although 18,000ft (5,500m) was preferred if conditions permitted, and it had to be released at least 3 miles (5km) from the target. The greater release height reduced the threat of anti-aircraft fire, which was especially important as the carrier aircraft had to maintain a steady course to keep the gliding bomb on target. It was essential that the device remained in sight of the controller and a flare was fitted in the tail to assist with this. In practice the carrier aircraft had to decelerate upon release, achieved by climbing slightly and then dipping back down, so that inertia would place the bomb ahead of the aircraft.

Fritz X had been launched from a Heinkel He 111 during testing, but in operation the Dornier Do 217 K-2 medium-range bomber became the main carrier. It was first deployed in July 1943 in an attack on Augusta harbour in Sicily, but its greatest success was with the sinking of the Italian battleship Roma on 9 September 1944. Bombers equipped with Fritz X also saw action at Salerno against American and British vessels. It is estimated that almost 1,400 Fritz X bombs were produced in total, including those used in flight testing.

Unlike the Fritz X the Henschel Hs 293 anti-shipping guided missile did have a liquid-fuelled rocket engine, slung beneath its belly, to allow operation at lower altitudes and from a far greater distance – estimated at up to 10 miles (16km). Designed by Professor Herbert Alois Wagner, the Hs 293 project was started in 1939 on the pure glide bomb principle, but Henschel und Sohn added the rocket unit which provided a short burst of speed. Over 1,000 Hs 293s were manufactured and a variety of rockets were used, usually the Walter HWK 109-507, producing a thrust of 1,300lb (590kg), or the slightly more powerful BMW 109-511 with 1,320lb (600kg) of thrust. The main element of the weapon was a high-explosive 650lb (295kg) charge within a thin-walled metal casing creating, in essence, a demolition bomb. Measuring 12ft 6in (3.82m) wide, it had a pair of straight wings with conventional ailerons for control, plus a tail with side fins and a lower fin. While the Fritz X was intended for use against armoured ships, the Hs 293 was specifically for un-armoured vessels, hence the thinner casing. The missile was radio controlled via a joystick control box in the carrier aircraft, and flares attached to the rear ensured the operator maintained visual contact.

The Hs 293 was the first operational guided missile to sink a ship. The British sloop HMS Egret was attacked and sunk in the Bay of Biscay on 27 August 1943, with the loss of 194 of her crew. Numerous other Allied vessels were also sunk in the Mediterranean.

The Allies’ efforts to counter the German radio-controlled weapons by jamming the signals were given a boost when an intact Hs 293 was recovered from a Heinkel He 177 which had crashed on Corsica, and improvements made to the radio jamming equipment had a major impact on the weapon’s effectiveness. In response the Germans modified 100 Hs 293A-1s as Hs 293Bs with wire link, and as the television-guided Hs 293D, although neither of these were operational by the end of the war. The Hs 293H was an experimental air-to-air variant.

Book title

The Rheintochter RIII’s liquid-fuel rocket engine on display at RAF Cosford. (JC)

With the experience gained with the Hs 293, Henschel developed several other anti-shipping guided missiles along the same principle. The Hs 294 was designed specifically to penetrate the water and strike a ship below the waterline, and consequently it resembled the Hs 293 but with a sleeker conical nose and two Walter 109-507D rockets mounted tight up against the wing roots. On the Hs 293F the Henschel engineers experimented with a delta wing configuration without a tail unit. The Hs 295 featured an elongated fuselage with enlarged, slightly bulbous warhead and the wings from the Hs 294, while the Hs 296 combined the rear fuselage of the Hs 294 with the control system of the Hs 293 and the bigger warhead of the Hs 295.

BATTLEFIELD ROCKETS

Rockets were also developed to augment or supplant the army’s conventional surface artillery. Rheinbote (‘Rhine messenger’) was developed by the Rheinmetall-Borsig company in 1943. Strictly speaking this slender four-stage rocket cannot be classified as a smart bomb as it was aimed solely by the positioning of the launcher and possessed no internal or external guidance systems. Apart from the V-2 (A4) this was the only other long-range ballistic missile to enter service during the Second World War.

The biggest drawback with conventional artillery is that the guns are often too heavy to be easily and swiftly transported to where they are needed, especially in a fast-moving battlefield. This had not been an issue in the opening stages of the war when the German Blitzkrieg spread with great rapidity thanks in no small measure to the Luftwaffe’s overwhelming aerial superiority and the ability to provide airborne bombardment in support of the ground forces. But the big guns had other drawbacks. Their range was limited and while the biggest guns bombarding Paris in the First World War might have had a range of just over 62 miles (100km), their huge size made them virtually immobile. Conventional artillery also required a constant supply chain to feed the guns. Rockets, on the other hand, had enormous range and were far more easily transported, although there might be an issue with accuracy. The Rheinbote project was initiated to put the battlefield rocket concept to the test.

Book title

A US Air Force officer examines an unidentified rocket-propelled guided bomb. Said to be just 8ft long (2.5m) it was most probably a test model. (CMcC)

In appearance Rheinbote was a slender spike 37ft (11.4m) long, with stabilising fins at the rear and three sets of smaller fins arranged at the end of each of the four stages. The rockets were fuelled by diglycol-dinitrate solid-fuel propellant and in tests achieved a blistering Mach 5.5, or 4,224mph (6,800km/h), the fastest speed of any missile at the time. Rheinbote was transported and launched from a modified V-2 (A4) rocket trailer which had an elevating launch gantry. The missile was aimed by orientating the trailer itself and elevating the gantry, although the accuracy of this method of aiming is highly questionable.

In tests the Rheinbote carried an 88lb (40kg) warhead, only 6.5 per cent of the missile’s total mass, up to 48 miles (78km) into the atmosphere to a range of up to 135 miles (220km), but for shorter ranges some of the stages could be removed. Over 200 were produced and they were used in the bombardment of Antwerp from November 1944 into early 1945. After the war ended the Soviets helped themselves to the designs at Rheinmetall-Borsig’s Berlin-Marienfelde headquarters, but in general the Rheinbote was considered to be lacking accuracy, thanks partly to the effect of the stage separations, and lacking punch as the payload was too small and the almost vertical high-speed delivery tended to bury it deep into the ground.

Time and time again the question is asked why these sophisticated and deadly weapons failed to turn the tide of war in Germany’s favour. And just as with the aircraft the same answer invariably comes back: it was too little too late. Time and resources had been squandered in developing a multitude of missile projects instead of focussing on a few well-defined goals. Priorities were in a constant state of flux and by the time those projects which had any potential were put into production resources had either become stretched to the limit or they were being misdirected into other areas. As Albert Speer commented in his memoirs, Inside the Third Reich:

    I am convinced that substantial deployment of Wasserfall from the spring of 1944 onward, together with an uncompromising use of jet fighters as air defence interceptor, would have essentially stalled the Allied strategic bombing offensive against our industry. We would have been well able to do that – after all, we managed to manufacture 900 V-2 rockets per month at a later time when resources were already much more limited.

By the final stages of the war the measures to defend the Reich were becoming ever more ingenious, and more desperate.

If you find an error please notify us in the comments. Thank you!