BACHEM’S BUDGET INTERCEPTOR

Another German rocket interceptor that posed an extreme risk to its own pilots was the Bachem Ba 349. This was really a surface-to-air anti-aircraft missile with a pilot on board to compensate for the absence of sufficiently advanced electronics, and was designed in response to a request by the Luftwaffe’s Emergency Fighter Program in early 1944 for a ‘Verschleissflugzeug’ (literally ‘Wear-and-tear Aircraft’, meaning a short-life aircraft). The situation had changed dramatically since the start of the war. Gone were ‘Blitzkrieg’ (Lightning War) and aerial supremacy for the Luftwaffe. The war had become one of attrition, and Germany, its heartland now under attack, was unable to compete with the industrial might of the US. The Luftwaffe no longer ruled the skies over the occupied countries, and was rapidly losing control of the airspace above Germany. Some radical defense system was needed to stop the Allied bombers from destroying the German industries, cities and transportation infrastructure. This new weapon had to be introduced as soon as possible, not require much scarce raw materials such as airplane-grade metals, and be easy to operate by pilots with little training (since by then most of the experienced pilots had either been killed or were prisoners of war). Moreover, the new aircraft would preferably not need runways or other vulnerable ground facilities that could be easily found and destroyed by enemy bombers.

Outsider Erich Bachem, who had left Fieseler in order to set up a small company to manufacture parts for aircraft, devised a truly radical design which fitted the need. His ‘Projekt BP 20’ was a rocket interceptor to be made mostly using cheap wooden parts, glued and screwed together. Its configuration was extremely simple, having a tube-shaped fuselage, two straight stubby wings and a T-shaped tail. Roll control was by differential use of the rudders on the lower and upper vertical fin (moving one to the left and the other to the right) so the wings required no moving parts. It would use few ‘war-essential’ materials reserved for other aircraft and be easy to build in volume by semi-skilled labor: a BP 20 could be constructed in only about 1,000 man­hours. Moreover, owing to the design’s simplicity most of the parts could be made in small woodworking shops distributed throughout Germany without interfering with aircraft production in factories which were already at peak capacity. Because of its distributed nature, production would also be relatively safe from sudden destruction by enemy bombers.

The BP 20 would be launched straight up while being controlled from the ground, and the pilot would bail out at the end of the flight. That way the pilots would not require training in the most difficult aspects of flying, which are take-off and landing. Bachem proposed to build large numbers of launch platforms around key industrial targets so that his interceptors would deter Allied bombers sufficiently for them to leave those targets alone. The RLM’s response was less than enthusiastic so Bachem showed his plan to Heinrich Himmler, chief of the security forces. Himmler, eager to increase his influence in the Third Reich, agreed to fund the development and placed an order for 150 machines paid with SS funds. Himmler, of course, intended that the interceptors be flown by SS men. By saving Germany from the “bomber menace” he would increase his own power in the Nazi government. Not wanting to be left out, the RLM later placed an order for another 50 interceptors for the Luftwaffe. The highly classified project was assigned top priority and the operational vehicle became the Ba 349, code-name ‘Natter’ (Viper).

Layout of the Bachem Natter.

If flying the Me 163 was a pretty brave thing to do, getting into a Natter should be considered truly heroic. Or rather, suicidal. The flight would start with the wooden contraption standing upright against a 15 meter (50 feet) tall, open-structure launch tower (or even just a modified telephone pole) with three vertical tracks engaging the wingtips and the edge of the ventral fin. The pilot would climb in, lie on his back in a seat angled at 90 degrees, and wait for the bombers to come within range. The entire gantry could turn around its vertical axis to enable the Natter to be oriented correctly depending on the direction the bombers were coming from. On command, the ground crew would take cover and the pilot would test the flight controls. Then he would start the central Walter HWK 109-509A engine (similar to that of the Me 163B) and verify its functionality. Next he would ignite the four solid propellant Schmidding rocket boosters, two strapped to each side. These delivered a total thrust of 47,000 Newton and because the vehicle weighed only 2,200 kg (4,850 pounds) they could readily lift it off the ground. Riding the tower, which provided initial stabilization, the machine would soon build up enough speed for the aerodynamic surfaces to keep it flying straight. The flight controls would remain locked in the neutral position until the solid boosters burned out, some 10 seconds into the flight. The initial acceleration was nearly 2 G, meaning twice as strong as the acceleration of gravity (i. e. the Natter would accelerate upwards about twice as fast as it would fall, because the total thrust was twice its total weight at lift-off). Hence at that moment the pilot would feel three times his normal weight, a combination of one G force of gravity plus the two G of the acceleration. When the strap-on boosters burned out they would be jettisoned by explosive bolts, the flight controls would unlock, and the autopilot would begin to steer to its assigned target using guidance commands received from the ground by radio. The vehicle would continue to climb under power of the Walter engine alone, accelerating at a rate of about 0.7 G to a maximum velocity of 700 to 800 km per hour (435 to 500 miles per hour). It would be guided towards a position in front of the bombers at an altitude of 9 km (30,000 feet), and only then would the pilot take over for the final phase of the attack. During the automatic phase of the flight the pilot was required to hold on to hand grips to prevent him from accidentally pulling on the control column while under the force of acceleration.

Closing in on his victim, the pilot would jettison the plastic nose cone to reveal a battery of missiles in front of the cockpit: either 24 R4M ‘Orkan’ (Hurricane) missiles of 3.5 kg (8.0 pounds) each, or 33 Henschel Hs 217 ‘Fohn’ (Warm Wind) rockets of 2.6 kg (6 pounds) each. Pulling the trigger would fire all of the unguided anti-aircraft missiles at the target in a single devastating salvo. Since the Natter would have little time for the attack, it made more sense to pack all its firepower into a single punch than to use conventional cannon more suitable for repeated precision strikes. Shortly after the missiles were fired, the engine would exhaust its propellant and the pilot would quickly glide at high speed down to an altitude of about 3 km (10,000 ft), where he would jettison the entire nose section, release his safety harness and fold the control column forward, an action that would release a braking parachute from the rear of the vehicle. The pilot would be thrown out by the sudden deceleration and subsequently deploy his own parachute. The tail with the engine, the most precious part of the aircraft, would land under the braking parachute to be refurbished and used again; only the nose section would be lost.

Development commenced with scientists of the Technical University of Aachen calculating the Natter’s aerodynamics using a large analog computer. The Deutsche Versuchsanstalt fur Luftfahrt (DVL) in Braunschweig then tested models in a wind tunnel. The results showed that the Natter would behave “satisfactorily” up to speeds of about Mach 0.95. In the meantime the solid propellant boosters were tested at the Bachem-Werke factory in Waldsee. Due to the high priority given by the SS to the development, less than 4 months after Bachem made his initial design sketches three full sized Natter prototypes were completed.

On 3 November 1944 the Ml (first) prototype, which took off from a trolley, was towed to an altitude of 3 km (10,000 feet) by a Heinkel He 111 bomber. Pilot Erich Klockner made various tests of the control and stability of the machine, discovering it to be rather sensitive and to react pretty violently to small movements of the stick. Due to the plane’s bucking and shaking he could not finish the test flight as planned with a realistic drop of the forward section, bail-out and retrieval of the tail section, so he decided simply to eject the cabin roof and jump out. The roof got caught at the hinge and did not fall away entirely, but Klockner managed to bail out from the side and landed safely by parachute. The Heinkel tow plane tried to land with the pilotless prototype, but without active control and lacking an undercarriage it hit the ground hard, tumbled end over end and was destroyed. Klockner went on to make several flights with the М3, which was fitted with a fixed undercarriage, each time bailing out successfully while the tow plane landed with the complete Natter behind it. The Natter design clearly did fly, but the tests showed that the dynamics of the tow cable and the aerodynamic influence of the fixed undercarriage had adverse effects on its stabihty. A free glide without the undercarriage would be required to unambiguously determine the Natter’s flight characteristics. Klockner refused, convinced that more tests and modifications were needed before such a flight could be made. The SS did not approve of his criticism and he was kicked out of the project.

The SS found another guinea pig, and on 14 February 1945 Luftwaffe test pilot Hans Ziibert took off in M8 towed by an He 111 bomber. Like the Ml, the M8 took off from a jettisoned trolley and once in the air was as aerodynamically ‘clean’ as the envisioned operational Natter. At an altitude of 5.5 km (18,000 feet) Ziibert released himself from the tow plane and pushed the plane into a steep (75 degree) nose dive to gain speed, then leveled off to execute a series of flight control tests. He found that the plane handled well at the attained maximum speed of about 600 km per hour (370 miles per hour) and that its stall velocity was about 200 km per hour (125 miles per hour). As per the test plan he then tried to deploy the braking chute, only to find that the release lever was stuck. Next he tried to eject the nose by activating the explosive bolts that held it to the rest of the vehicle but again nothing happened. It was time to get out: Ziibert ejected the cabin hood, put the plane into a steep climb to bleed off speed and struggled to escape. When just 1,200 meters (3,900 feet) above the ground and flying at 300 km per hour (190 miles per hour) the Natter went into a spiral dive. Ziibert hung on for three full turns, then dived over the left wing, passing beneath the tail unit. He landed safely by parachute but the M8 smashed into the ground at high speed. Of this flight Ziibert reported: “My general impression of the machine is very good and I can describe its flying characteristics as very benign.” The reason for the braking parachute failing to release was that a screw was blocking the release lever. The screw had been inserted in order to prevent inadvertent deployment of the chute on the ground, and the technicians had forgotten to remove it just before flight.

In parallel with these gliding flights a series of unmanned vehicle launches tested the rocket boosters, the Walter motor and the autopilot. Beginning on 18 December 1944, fifteen of these were shot into the sky from the Lager Heuberg military training area near Stetten am kalten Markt. These tests led to the abandonment of the plan to reuse the Walter engine, because it invariably got damaged by the rather hard impact of the parachute landing. The tests also proved that the thrust of the boosters varied by as much as 50% either way, making the stability of the vehicle very unpredictable during its initial boosted ascent.

Preparations on the launch pad for the flight of an unmanned test version of the Natter.

Launch of an unmanned Natter prototype.

By early 1945 Germany had all but lost the power to defend its own airspace and, driven by desperation, the SS ordered a manned Natter launch even though many of the unmanned test flights had ended in crashes and explosions. The SS found a pilot willing to risk his Ufe in Lothar Sieber, a Luftwaffe Second Lieutenant who had been demoted to the rank of Private after drinking alcohol on duty, and who hoped that his flight would restore his previous rank. On 1 March Sieber got into Ba 349A1 number M23 at the Lager Heuberg military area. The booster rockets were ignited and the wooden contraption raced along its launch rail and shot straight up, thereby making Sieber the first person to be launched vertically from the ground by rocket power. He did not have much time to enjoy this accomplishment though, because after climbing about 100 meters (330 feet) the machine suddenly turned over on its back and lost its cockpit cover. Since this cover included the headrest it is likely that the acceleration snapped Sieber’s head back against the fuselage, at least rendering him unconscious and perhaps even snapping his neck. The Natter reached a peak altitude of about 450 meter (1,500 feet) some 15 seconds into the flight, then it dived essentially vertically into the ground. Whether the cover had not been installed correctly or had simply not been sufficiently closed was never discovered. Sieber was posthumously promoted to First Lieutenant. Development and testing continued

US soldiers with a Natter.

using unmanned prototypes but it was clear that the Natter would not be ready for service before the Allies overran Germany. And of course its use would be limited owing to the scarcity of the special propellants required for the Walter engine. Thus no Natter was ever launched against an Allied bomber. After the war, US forces found many Natters in various states of completion. One of those that they took back to America for evaluation is currently awaiting restoration at the National Air and Space Museum’s Steven F. Udvar-Hazy Center close to Washington Dulles International Airport.

A high-fidelity Natter replica is on display at the Fantasy of Flight Museum in Florida. Looking at this crude wooden tube with its small wings, you cannot imagine anyone volunteering to pilot it, to be shot up at close to 800 km per hour (500 miles per hour) to attack a fleet of heavily armed bombers. The Planes of Fame Air

Museum’s Chino location in California has a full scale model that was built by hobbyist George Lucas (not to be confused with the creator of Star Wars), who also made the full-scale model of the Me 163B that is on display in the same museum. In Europe a Ba 349A replica is displayed in the Deutsches Museum in Munich, Germany, featuring realistic colors and markings of one of the unmanned test aircraft. On its horizontal stabilizers there is an authentic-looking text promising a reward to anyone who finds the tail section and returns it to the military, evidently because some units were expected to drift out of the test area while descending on their parachute. Another German museum, the Stettener museum located near the place where the Natters made their test flights, shows a replica of the one flown by Sieber. It is depicted standing against the launch tower with mannequins of Bachem and Sieber in front of it in discussion about the upcoming flight. At the time of writing, a group in Speyer, Germany, is also building a detailed replica of a Natter according to the original plans. This is intended to be flightworthy except for the rocket propulsion, but it is not actually meant ever to take to the sky. Eventually the team hopes to build a small series of ten aircraft.

The Natter was basically a guided surface-to-air missile with the pilot acting as its control system; a job that was soon taken over by electronics in the new air defense missiles that became operational after the war. These were smaller and lighter than a human, did not require training, and were cheap enough not to require retrieval after use. The Ba 349 remains unique as the first, and last, piloted air defense missile. It is interesting to note that the Natter bears similarities to the Space Shuttle in that both were crewed, vertically launched, liquid propellant rocket planes that had jettisonable solid propellant boosters for take-off, with the liquid propellant motors being started and checked (and stopped, if needed) prior to igniting the boosters, at

Natter replica in the Fantasy of Flight Museum in Florida [Rogier Schonenborg].

which moment there was no way to prevent the vehicle from leaving the ground. In 1952 Bachem noted, “within a few months we had to track down, go through and solve numerous problems associated with vertical take-off, problems which the designers of future spacecraft will also have to look at”, and also, “The attainment of great goals is not possible by a single leap, it is the result of an arduous climb up a steep ladder, step by step! Perhaps through our labor we have constructed one rung on that ladder!” Although true, these words appear to impart too much philosophical meaning to what was basically a last-ditch, near-suicidal weapon system.

Erich Bachem remained in Germany after the war and resumed his innocent pre­war business of designing and building camping trailers and motor homes. He joined the business of a neighbor, Erwin Hymer, whose company is still manufacturing recreational vehicles and camping trailers in the same buildings in which Bachem’s rocket interceptors were made. One of Hymer’s popular lines of camping trailers is called ‘Eriba’, Bachem’s nickname as a student derived from ERIch BAchem. You can thus still ride a Bachem, not at transonic speeds but certainly at less risk to your life.