The Bachem Ba 349 Natter () is a German rocket-powered point-defence interceptor that was developed during the latter portion of the Second World War.
The Ba 349 was to be deployed in a very similar way to a manned version of the surface-to-air missiles under development in the Reich. A typical mission profile started with a rapid vertical take-off (the time to altitude being 62 seconds to , which eliminated the need for conventional airfields, while the majority of the flight towards Allied bombers was to be controlled by an autopilot, making it feasible to be flown by relatively untrained pilots. The primary role of the pilot was to aim the aircraft at a target bomber and to fire rockets housed in the aircraft's nose cone. After completing their attack run, the pilot would dive their Natter to a lower altitude before, using separate parachutes, the pilot and the fuselage containing the rocket engine would land separately and be recovered. The nose section was disposable, hence the aircraft being classified as being semi-expendible.Green 1971, p. 127.
The Natter was first conceived of during August 1944 as the BP-20 by Erich Bachem amid a pressing military need to counter the Allied strategic bombing offensive being waged against Nazi Germany. While not designed to fulfil the specification for the Emergency Fighter Program, it was designed for the same purpose. Accordingly, the Natter was designed to be constructed by unskilled labour using low-tech tooling and affordable materials wherever possible, being largely composed of wood. After securing the backing of Reichsführer-SS Heinrich Himmler, the BP-20 was quickly refined into the Ba 349; the first experimental prototype Natter, Versuchsmuster 1 was completed on 4 October 1944. Several prototypes underwent testing in level flight, towed and free gliding, and unmanned vertical flights. The first and only manned vertical take-off flight, conducted on 1 March 1945 near Stetten am kalten Markt, ended in the death of the test pilot, Lothar Sieber, due to a canopy failure. During the one-minute flight, about were travelled in total, at a calculated average speed of about . No operational flights were ever conducted; at least one Natter was transported to the US for evaluation after the end of the conflict.
Development Background In 1943, the air superiority of the Luftwaffe was being challenged by Allied aircraft over the Reich; seeking to overcome this crisis, German officials urgently sought out radical innovations and unconventional solutions to respond to the threat posed by Allied airpower.Green 1971, p. 124. The emerging field of surface-to-air missiles appeared to be a promising approach against the Allied strategic bombing offensive; a variety of projects were started, but invariably problems with the guidance and homing systems prevented any of these from attaining operational status.Dryden 1945, pp. 1–11. Providing the missile with a pilot, who could operate a weapon during the brief terminal approach phase, offered a solution.
Submissions for a simple target defence interceptor were requested by the Luftwaffe in early 1944 under the umbrella of the , literally "Emergency Fighter Program".Proctor 1945 Pabst 1984, p. 166. A number of simple designs were proposed, including the Heinkel P.1077 Julia, in which the pilot lay prone (on his stomach), to reduce the frontal area.Green 1971, pp. 124-125. Following a series of evaluations by the Reichsluftfahrtministerium (RLM, Ministry of Aviation), the Julia would become the front-runner to fulfil this requirement in autumn 1944. The initial plan was to launch the aircraft vertically, but this concept was later changed to a conventional horizontal take-off from a tricycle-wheeled trolley, similar to that used by the first eight prototypes of the Arado Ar 234 Blitz jet reconnaissance bomber.Bachem 1944b.Green 1971, p. 125.
Bachem's proposal The Natter was first conceived by the aeronautical engineer Erich Bachem in August 1944, after witnessing an American bombing raid on a major German city. He believed there ought to be a way to break up these large formations of bombers. His BP-20 ("Natter") was a development from a design he had worked on at Fieseler, the Fi 166 concept, but considerably more radical than the other submissions.Green 1970, p. 65. It was built using glued and nailed wooden parts with an armour-plated bulkhead and bulletproof glass windshield at the front of the cockpit. The initial plan was to power the aircraft with a Walter HWK 109-509A-2 rocket engine; however, only the 109-509A-1, as used in the Me 163, was available.Gooden 2006, pp. 124–127. It had a sea level thrust variable between at "idle" to at full power, with the Natter's intended quartet of rear flank-mount Schmidding SG34 solid fuel rocket boosters used in its vertical launch to provide an additional thrust for ten seconds before they burned out and were jettisoned. The experimental prototypes slid up a -tall vertical steel launch tower for a maximum sliding length of in three guideways, one for each wing tip and one for the lower tip of the ventral tail fin. By the time the aircraft left the tower it was hoped that it would have achieved sufficient speed to allow its aerodynamic surfaces to provide stable flight.Reyle 1998, pp. 70–73.Bachem-Werk 1944, pp. 183–185.
Under operational conditions, once the Natter had left the launcher, it would be guided to the proximity of the Allied bombers by an autopilot with the possibility of an added beam guidance similar to that used in some V-2 rocket launches.Green 1971, p. 133. Only then would the pilot take control, aim and fire the armament, which was originally proposed to be a salvo of nineteen R4M rockets.Bachem 1944aGreen 1971, p. 130. Later, 28 R4Ms or a number of the larger, Henschel Hs 297 Föhn rockets were suggested,Köster 1944. with either variety of unguided rocket fired from the Natter's nose-mounted cellular launch tubes. The Natter was intended to fly up and over the bombers, by which time its Walter engine would probably be out of propellant. Following its one-time attack with its rockets, the pilot would dive his Natter, now effectively a glider, to an altitude of around , flatten out, release the nose of the aircraft and a small braking parachute from the rear fuselage. The fuselage would decelerate and the pilot would be ejected forwards by his own momentum and land by means of a personal parachute.Christopher, p. 153.Green 1971, pp. 131, 133.
In an early proposal in August 1944, the Natter design featured a concrete nose; it was suggested that the aircraft might ram enemy bombers,Green 1971, pp. 130-131. but this proposal was subsequently withdrawn in later Project Natter outlines. Bachem stated clearly in the initial proposal that the Natter was not a suicide weapon and much effort went into designing safety features for the pilot. However, owing to the potential dangers for the pilot inherent in the operation of this precarious aircraft, the Natter has sometimes been listed as a suicide craft.German Suicidal Aircraft The design had one decisive advantage over its competitors – it eliminated the necessity to land an unpowered glider at an airbase, which, as the history of the Me 163 rocket interceptor had clearly demonstrated, left an aircraft extremely vulnerable to attack by Allied fighters.Ethell 1978, pp. 94–144.
Modifications Bachem approached Adolf Galland, a Luftwaffe general and flying ace, after which Galland personally recommended its development to the RLM. The RLM's technical department allegedly took a poor view of this approach, viewing it as unorthodox and meddlesome. Furthermore, the semi-expendable nature of the Natter meant that it did not conform with the existing specification issued for the Emergency Fighter Program. Bachem refused to be discouraged and sought out other politically-influential figures to support the Natter concept. He was granted an interview with Heinrich Himmler, the Reichsführer-SS, who quickly gave his full support to the Natter. Within 24 hours, Bachem was informed that the RLM's technical department was reconsidering their rejection and that the project had received the highest development priority. Accordingly, in mid-September 1944, the Technical Office of the Waffen-SS issued an order for Bachem to develop and manufacture the Natter at his Waldsee factory.Grieger 1990, p. 26.Green 1971, pp. 127, 130. The RLM officially designated the BP-20 as the Ba 349A and construction began.
During December 1944, the project came largely under the control of the SS and Obergruppenführer Hans Kammler.Felkin 1945 This decision has been claimed to have been the only occasion that the SS would significantly interfere with aircraft design and air fighting strategy.Speer 2001, p. 215. At an early stage if the project, the RLM undertook an engineering assessment of the Natter, the report for which was issued on 28 October 1944.Magerstädt 1944 The Natter was designed to be built by unskilled labour with poor-quality tools and inexpensive material. Various stringent economies were imposed on an already frugal design. The airframe of the Natter was almost entirely composed of wood.Green 1971, p. 131. It also lacked landing gear, which saved weight, expense and construction time. Consequently, one of the most unusual features of the machine was the escape of the pilot and recovery of the machine.
The proposed sequence of these events was as follows: After the attack, the Natter might dive to a lower altitude and flatten out into level flight. The pilot would then proceed with a well-practised escape sequence. He would open the cockpit canopy latch, which would allow the canopy to flick backwards on its hinge in the airstream. Next, the pilot would undo his seat belt and remove his feet from the rudder pedal stirrups. By squeezing a lever mounted on the control column, he would release a lock at the base of the column, which would allow him to tilt the column forwards where it could engage in and undo a safety latch for the nose release mechanism. He would then lean a little further forward and pull a lever hinged near the floor at the front of the cockpit, freeing the nose section, which self-jettisoned as a result of the reduced aerodynamic pressure at the front of the fuselage. As the nose section separated, it was intended to briefly pull on two cables that released a small ribbon parachute stored on the starboard side of the rear fuselage. The parachute subsequently opened and decelerated the Natter. The pilot would be ejected from the cockpit by his own momentum and as soon as he was clear of the fuselage, he would open his personal parachute and descend to the ground.Gooden 2006, pp. 101–102. A parachute was intended to eject the valuable Walter rocket engine from the rear, which would decelerate the aircraft and eject the pilot with inertia, however, associated problems with this mechanism were still not fully resolved prior to the conflict's end.
Wind tunnel testing on a wooden model, scaled to 40% of full size, was performed at the Deutsche Versuchsanstalt für Luftfahrt (DVL), the Institute for Aerodynamics at Berlin-Adlershof in September 1944 at speeds up to . Results from these tests were reported in January 1945 to the Bachem-Werk.Wacke 1945, p. 218. Further model tests were carried out at the Luftfahrtforschungsanstalt Hermann Göring (LFA) facility in Völkenrode-Braunschweig, at speeds close to Mach 1.Millikan 1945, p. 14. In March 1945, the Bachem-Werk simply received a statement that satisfactory flying qualities should be expected with speeds up to .Bratt 1945
Flight testing