Editing Bachem Ba 349 Natter (section)

==Development==
===Background===
In 1943, ''[[Luftwaffe]]'' air superiority was being challenged by the Allies [[defence of the Reich|over the ''Reich'']] and radical innovations were required to overcome the crisis. Surface-to-air missiles appeared to be a promising approach to counter the [[Combined Bomber Offensive|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.<ref>Dryden 1945, pp. 1–11.</ref> 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 {{Lang|de|Jägernotprogramm}}, literally "[[Fighter Emergency Program|Emergency Fighter Program]]".<ref>Proctor 1945 {{page needed|date=November 2022}}</ref><ref>Pabst 1984, p. 166.</ref> 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.

The ''Julia'' was the front-runner for the contract. 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]] jet reconnaissance bomber.<ref>Bachem 1944b.</ref>

===Bachem's proposal===
The Natter was first conceived by Dr [[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.{{Sfn|Aeronautical Staff of Aero Publishers|1966|p=35}} His BP-20 ("Natter") was a development from a design he had worked on at Fieseler, the [[Fieseler Fi 166|Fi 166]] concept, but considerably more radical than the other submissions.<ref>Green 1970, p. 65.</ref> 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 machine with a [[Walter HWK 109-509]]A-2 rocket engine; however, only the 109-509A-1, as used in the [[Messerschmitt Me 163 Komet|Me 163]], was available.<ref>Gooden 2006, pp. 124–127.</ref> It had a sea level thrust variable between {{convert|100|kg|abbr=on}} at "idle" to {{convert|1,600|kg|abbr=on}} 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 {{convert|4,800|kg|lb|abbr=on}} thrust for 10 seconds before they burned out and were jettisoned. The experimental prototypes slid up a {{convert|20|m|ft|abbr=on}}-tall vertical steel launch tower for a maximum sliding length of {{convert|17|m|ft|abbr=on}} 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.<ref name="Reyle 1998, pp. 70-73">Reyle 1998, pp. 70–73.</ref><ref>Bachem-Werk 1944, pp. 183–185.</ref>

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. Only then would the pilot take control, aim and fire the armament, which was originally proposed to be a salvo of nineteen 55mm [[R4M]] rockets.<ref name="Bachem 1944a">Bachem 1944a</ref> Later, 28 R4Ms or a number of the larger, 73mm [[Henschel Hs 297]] ''Föhn'' rockets were suggested,<ref>Köster 1944.{{page needed|date=June 2014}}</ref> 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 {{convert|3,000|m|ft|abbr=on}}, 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.<ref>Christopher, p. 153.</ref>

In an early proposal in August 1944, the Natter design had a concrete nose; it was suggested that the machine might ram a bomber, 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.<ref name="Bachem 1944a"/> However, owing to the potential dangers for the pilot inherent in the operation of this precarious aircraft, the Natter is sometimes listed as a suicide craft.<ref>[http://discaircraft.greyfalcon.us/German%20Suicidal%20Aircraft.htm German Suicidal Aircraft]</ref> The design had one decisive advantage over its competitors – it eliminated the necessity to land an unpowered gliding machine at an airbase, which, as the history of the Me 163 rocket aircraft had clearly demonstrated, made an aircraft extremely vulnerable to attack by Allied fighters.

===Modifications===
[[Heinrich Himmler]] became interested in Bachem's design. The [[Reichsführer-SS]] granted Bachem an interview and fully supported the project. In the middle of September 1944, the Technical Office of the [[Waffen-SS]] made an order for Bachem to develop and manufacture the Natter at his [[Bad Waldsee|Waldsee]] factory.<ref>Grieger 1990, p. 26.</ref> The [[Reichsluftfahrtministerium]] (RLM/German Aviation Ministry) officially designated the BP-20 the Ba 349A and construction began.{{Sfn |Aeronautical Staff of Aero Publishers|1966| p =  35}} During December 1944, the project came largely under the control of the SS and [[Obergruppenführer]] [[Hans Kammler]].<ref>Felkin 1945 {{page needed|date=November 2022}}</ref> This decision is said to have been the only time the SS significantly interfered with aircraft design and air fighting strategy.<ref>Speer 2001, p. 215.</ref> Early-on in the project, the RLM undertook an engineering assessment of the Natter, which it reported on 28 October 1944.<ref>Magerstädt 1944 {{page needed|date=November 2022}}</ref>

The Natter was designed to be built by unskilled labor with poor-quality tools and inexpensive material.<ref name="ley194811">{{Cite magazine |last=Ley |first=Willy |date=November 1948 |title=The 'Brickwall' in the Sky |url=https://archive.org/stream/Astounding_v42n03_1948-11_cape1736#page/n77/mode/2up |magazine=Astounding Science Fiction |pages=78–99}}</ref> Various stringent economies were imposed on an already frugal design. The Natter had no 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.<ref>Gooden 2006, pp. 101–102.</ref>{{r|ley194811}} A parachute was to eject the valuable Walter rocket engine from the rear, which would decelerate the aircraft and eject the pilot with inertia,{{r|ley194811}} however, associated problems with this mechanism were still not fully resolved prior to the conflict's end.{{CN|date=November 2022}}

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 {{convert|504|km/h}}. Results from these tests were reported in January 1945 to the Bachem-Werk.<ref>Wacke 1945, p. 218.</ref>{{r|ley194811}} Further model tests were carried out at the ''[[Luftfahrtforschungsanstalt]] Hermann Göring'' (LFA) facility in [[Völkenrode]]-Braunschweig, at speeds close to [[Mach number|Mach]] 1.<ref name="Millikan 1945, p. 14">Millikan 1945, p. 14.</ref> In March the Bachem-Werk simply received a statement that satisfactory flying qualities should be expected with speeds up to {{convert|1,100|km/h}}.<ref name="Bratt 1945">Bratt 1945 {{page needed|date=November 2022}}</ref>

===Flight testing===
Construction of the first experimental prototype ''Natter, Versuchsmuster 1'', was completed on 4 October 1944. V1 was subsequently referred to as ''Baumuster1'' (''BM1'') and later still the "B" was dropped and the machine became known as the M1. Most subsequent prototypes were known by 'M' codes, as the later prototypes of the [[Heinkel He 162]] were. Manned glider flights began on 3 November 1944. The first glider M1 was towed to around 3,000 m by a [[Heinkel He 111]] bomber with a cable (''Tragschlepp'' mode) at [[Neuburg an der Donau]]. The pilot was Erich Klöckner, who made all four documented ''Tragschlepp'' ("towed") flights.

After carrying out the test programme of the M1, he bailed out and the machine crashed into the ground.<ref>Klöckner 1944</ref> It was found that the towing cable, and in the case of the M3, the undercarriage interfered with the flight characteristics of the gliders and consequently the results were difficult to interpret.<ref name="Reyle 1998, pp. 70-73"/> To resolve doubts about the Natter in the glider mode, Hans Zübert made a free flight in the M8 on 14 February, and showed that the Natter was indeed a good flying machine.<ref>Zübert 1945 {{page needed|date=November 2022}}</ref>

The vertical take-off trials were conducted on high ground called the Ochsenkopf at the ''Truppenübungsplatz'' (military training area) Heuberg near [[Stetten am kalten Markt]], [[Württemberg]]. The first successful unmanned vertical take-off from the experimental launch tower occurred on 22 December 1944.{{Sfn |Aeronautical Staff of Aero Publishers|1966| p =  35}} The test machine, the M16, was powered only by the Schmidding solid boosters,<ref name=c4>Christopher, p. 154.</ref> as were all the early vertical launch trials. Up to and including 1 March 1945, 16 prototypes had been used, eight in glider trials and eight in VTO trials.<ref>Gooden 2006, pp. 114–115.</ref>

===Manned test flight===
By January 1945, Bachem was under pressure from the authorities in Berlin to carry out a manned flight by the end of February.<ref>de Bok 1978, pp. 104–109.</ref> On 25 February, M22 was in the experimental launch tower. It was as complete an operational machine as possible with the Walter HWK 109-509 A1 engine installed for the first time. A dummy pilot was in the cockpit. Lift-off from the tower was perfect. The engineers and ground crew watched as the M22 ascended under the combined power of the four Schmidding boosters and the Walter engine, an estimated total thrust of {{convert|6,500|kg|lb|abbr=on}}. The nose separated as programmed and the dummy pilot descended safely under its personal parachute. The remainder of the fuselage came down under its two large salvage parachutes, but when it hit the ground the Walter liquid-propellant rocket engine's residual [[hypergolic]] propellants (''[[T-Stoff]]'' oxidizer and ''[[C-Stoff]]'' fuel) exploded and the machine was destroyed.<ref>Lommel 1998, p. 92.</ref>

Despite Bachem's concerns that the test programme had been significantly cut short, a young volunteer ''Luftwaffe'' test pilot, [[Lothar Sieber]], climbed into the cockpit of the fully fuelled M23 on 1 March. The aircraft was equipped with an FM transmitter for the purpose of transmitting flight data from various monitoring sensors in the machine.<ref>Wilde 1945 {{page needed|date=November 2022}}</ref> A hard wire intercom appears to have been provided between Sieber and the engineers in the launch bunker using a system similar to that used in the manned glider flights. Around 1100 am, the M23 was ready for take-off. Low stratus clouds lay over the Ochsenkopf. The Walter liquid-fueled rocket engine built up to full thrust and Sieber pushed the button to ignite the four solid boosters.

Initially, the Natter rose vertically but, at an altitude of about {{convert|100|to|150|m|ft|abbr=on}}, it suddenly pitched up into an inverted curve at about 30° to the vertical. At about {{convert|500|m|ft|abbr=on}} the cockpit canopy was seen to fly off. The Natter continued to climb at high speed at an angle of 15° from the horizontal and disappeared into the clouds. The Walter engine stalled about 15 seconds after take-off. It is estimated the Natter reached {{convert|1500|m|ft|abbr=on}}, at which point it nose-dived and hit the ground with great force about 32 seconds later, some kilometres from the launch site.<ref name="Bachem 1952, pp. 89-96">Bachem 1952, pp. 89–96.</ref>{{r|ley194811}} Unknown at the time, one of the Schmidding boosters failed to jettison and its remains were dug up at the crash site in 1998.<ref>Pallud 2011, pp. 2–21.</ref>

The pilot was likely unconscious long before the crash.{{r|ley194811}} Bachem surmised Sieber had involuntarily pulled back on the control column under the effect of the 3 G acceleration. Examination of the canopy, which fell near the launch site, showed the tip of the latch was bent, suggesting it may not have been in the fully closed position at launch.<ref>Lommel 1998, photograph purporting to show the canopy from M23.</ref> The pilot's headrest had been attached to the underside of the canopy and as the canopy flew off the pilot's head would have snapped back suddenly about {{convert|25|cm|in|abbr=on}}, hitting the solid wooden rear upper cockpit bulkhead, and either knocking Sieber unconscious or breaking his neck.<ref>Bachem-Werk 1945a.</ref>

The accident reinforced Bachem's long held belief that the take-off and flight in the vicinity of the target bombers should be fully automated. The canopy latch was strengthened and the headrest was attached to the backboard of the cockpit. Before the introduction of the autopilot in the test programme, the control column would have a temporary locking device on it, which would allow the machine to ascend vertically to at least {{convert|1,000|m|ft|abbr=on}} and then be removed by the pilot.<ref>"Aktennotiz: Stellungnahme zu der Erprobung M23 (Senkrechtstart der bemannte Triebswerkmachine)." ''Sonderkommando der Waffen SS'' (Waldsee-Württemberg), March 1945.</ref> The Walter engine probably ceased operation because the Natter was virtually upside-down and air may have entered the intake pipes in the propellant tanks, starving the engine.<ref>Gooden 2006, p. 81.</ref> Sieber had become the first person to take off vertically from the ground under pure rocket power, 16 years before [[Yuri Gagarin]]'s ''Vostok 1'' pioneering, peacetime orbital flight. Following Sieber's death, all of the eight subsequent Natter flights were unmanned.<ref>Gooden 2019, p. 504.</ref>

===Production===
The SS ordered 150 Natters, and the ''Luftwaffe'' ordered 50, but none were delivered by the end of the war.{{r|ley194811}} Much debate has surrounded the number of Natters built at the Bachem-Werk and their disposition. According to Bachem, 36 ''Natters'' were produced at the Bachem-Werk in [[Bad Waldsee|Waldsee]] by the end of the war.<ref name=c4/>  Up to April 1945, 17 aircraft had been used in unmanned trials comprising five gliders, all slung under an He 111 in the ''Mistelschlepp'' configuration prior to launch, and 12 VTO examples. Five aircraft were prepared for manned trials, four gliders and one VTO version. The M3 was flown twice, and then rebuilt at which time it was given the new code BM3a but was never flown. The total number of launches to early April 1945 was 22, as was the total number of Natters constructed up to that time.<ref name="Bachem 1952, pp. 89-96"/> Bachem reported further that there were 14 more finished or almost finished aircraft in April 1945. Four of these were prototype A1 operational Natters built for test launching from a wooden pole launcher, which had been designed for field deployment.<ref>Bachem-Werk 1945b</ref> This new launcher was also constructed on the Heuberg, not far from the experimental steel tower. There is documentary evidence for two pole launches in April but not three as claimed by Bachem in his post-war presentation.<ref name="Bachem 1952, pp. 89-96"/> The documentation for this third flight may have been destroyed by the SS at war's end. Ten A1 operational Natters, called ''K-Maschinen'', were constructed for the ''Krokus-Einsatz'' ("Operation Crocus").<ref name="Reyle 1998, pp. 70-73"/>

The fate of these 14 A1 Natters was as follows:
Three were fired from the vertical launch tower according to Bachem, four were burnt at Waldsee, two were burnt at ''Lager'' Schlatt, [[Oetztal]], [[Austria]], four were captured by US troops at [[Sankt Leonhard im Pitztal]], Austria,<ref name="Bratt 1945"/> and one, which had been sent as a sample model to a new factory in [[Thuringia]], was captured by the [[Red Army]].<ref name="Bachem 1952, pp. 89-96"/> Consequently, the total of 36 test and operational aircraft constructed at the Bachem-Werk can be accounted for. However, Natter carcasses were used for a variety of ground-based purposes; for example, as a static booster rocket, armament and strength testing and pilot seat position tests. Some fuselages were reused after flight testing; for example, the M5, 6 and 7.<ref>Bachem-Werk 1945c</ref>

Of the four Natters captured at Sankt Leonhard im Pitztal, two went to the United States.<ref name="Gooden 2006, pp. 115-120">Gooden 2006, pp. 115–120.</ref> Only one original Natter built in Germany in the Second World War survives in storage at the [[Paul E. Garber Preservation, Restoration, and Storage Facility]] in [[Suitland, Maryland]], under the auspices of the [[Smithsonian Institution]]. The fate of the other Natter brought to the US is unknown. There is no documentary evidence that a Natter was ever flown from [[Edwards Air Force Base|Muroc Field]]. The tail section of one of the Natters at Sankt Leonhard im Pitztal was broken off while it still rested on its trailer.<ref>Gooden, Brett. ''Natter Photographic Archive,'' 2011.</ref>