The Bachem Natter was projected as a small lightweight expendable interceptor, capable of destroying enemy bombers using the least possible weapon expenditure. To achieve this objective, the project employed a vertical rocket-assisted take-off followed by separate descent and landing of pilot and aircraft by separate parachutes. It was believed that pilots would need only rudimentary flight and gunnery instruction, rather than spending valuable training resources on the finer points of flight training. Erich Bachem reasoned that, a reasonable number of such interceptors and launch sites could be installed around key industrial targets and inflicting such losses on attacking Allied bombers as to make their missions a prohibitively high price to continue.
In reality, only one proposal for an experimental vertical take-off interceptor was submitted in 1944. This project designated Bachem Projekt 20, was accepted by the Air Ministry and received the official RLM designation Ba 349 and code-named Natter (Viper). Despite ambitious plans, it was in fact only manufactured in small numbers prior to the end of the war. A second design again with vertical take-off capability, the HP 1077 failed to materialize except for a few gliders that may have been completed prior to the war's conclusion.
The Bachem Werke GmbH was founded on February 10 1942, by Erich Bachem, formerly the ‘Technischer Direktor’ of the Fieseler firm. The company mainly manufactured spare parts for piston-engine fighters and other aircraft equipment before the Natter project was created.
The Natter was of wood construction and, unlike other wooden aircraft like the Horten flyng wing, was to be built without the use of gluing presses. Most of the parts could be made in small woodworking shops through Germany without interfering with the existing needs of the aircraft industry. According to Erich Bachem only 600 man-hours would be required for the production of one airframe, excluding the HWK 509 A-2 rocket motor which was a relatively simple to manufacture when compared to sophisticated turbojet. The fuel capacity consisted of 450 litres of T-Stoff and 250 litres of C-Stoff, carried in separate tanks. This was sufficient for 80 seconds at full power, developing a thrust of about 3,750 lb (1,700 kg). Take-off assistance was provided by four solid-fuel rockets SR 34 which produced an additional thrust of 2,200 lb (1,000 kg) for twelve seconds.
Natter's weapon systems were simple and potentially devastating. This comprised either a honeycomb 24 electrically fired 73 mm F6hn air-to-air rockets, or 32 R40 air-to-air missiles located behind a jettisonable cover in nose. The alternative, the Rheinmetall SG 119 consisted of six clusters, each cluster containing seven MK108 barrels grouped together in a cylinder with the clusters arranged about the Viper's nose as in a revolver. Bachem submitted his Natter project to the OKL and simultaneously to the SS-F6hrungshaptamt (SS Planning Office), in August 1944. One month later, a contract for fifteen experimental BP 20 aircraft was awarded, and a few weeks later, Natter was included in the J5gerNotprogramm (Emergency Fighter Program).
The first experimental aircraft, the Ba 349 M1 and M2 were under construction by October 1944 and the RLM seemed convinced the Natter would be successfully employed against Allied heavy bombers in early 1945. The first batch of fifty Ba 349s was ordered for delivery between October 1944, and January 1945 and as a measure of the importance attached to the program, a substantial order of 200 Vipers was intended at the start of mass production.
Installation of parachutes delayed flight testing of the first target defence prototype (Ba 349 M1) until November 1944. The Ba 349 M2 with a fixed undercarriage was completed soon thereafter and the first take-off under air-tow of the third prototype, Ba 349 M3 with the same arrangement, was made at Neuburg on the Danube on December 14, 1944. A second flight behind a He 111 by the DFS, followed eight days later. After successful completion of ground tests near Bad Waldsee on December 18, 1944, the first powered vertical launch from a ramp was quickly scheduled.
This event however was marred when the Viper caught fire as a result of a technical fault. The next flight was made four days later at Heuberg Hill near Stetten am kalten Markt. This aircraft was towed to an altitude of 2,460 ft (750 m) and parachutes were deployed to carry the Viper and its simulated pilot safely to ground. A second owed take-off occurred on December 29, 1944, without serious incident before other Vipers were towed into the air for further testing.
Plans for mass production of the Ba 349 A-1 were authorized on March 1, 1945, but less than twenty Natters were built. These were followed by the improved Ba 349 B-1 (Entwurf 2) interceptors, also to be produced at Waldsee, but again few were actually completed.
A few models were powered by a solid-fuel rocket to evaluate take-off characteristics. Practical tests carried out at Peenemunde, where a first test conducted during February 1945, proved unsuccessful. Willy A. Fiedler, a testing engineer working for the RLM, was sent to the Heuberg Hills to oversee the program Erich Bachem is quoted after the war as having said that about twenty Vipers had been used for practical tests. Fifteen were of the A-series, and four B-series aircraft. All were constructed at Waldsee. Still others were assembled by the Wolf Hirth glider factory.( Four additional Ba 349s, possibly of the B-series, were captured at the end of the war by Allied forces near St. Leonhard, Austria).
Construction of the production Ba 349A models had actually started in October and a total of fifteen were launched over the next few months. Each launch resulted in some small modification to the design, and eventually these were collected into the definitive production version, the Ba 349B which started testing in January.
In February 1945 the SS funders decided that the program was not going fast enough, and demanded a manned launch later that month. The official record of the aircraft being tested in this way was on 1 March, when Lothar Sieber flew Ba 349A M23 and launched from the Lager Heuberg military training area near Stetten am kalten Markt. Take-off went well at first, but one of the jettisonable Schmidding boosters failed to release and pushed the Natter got out of control. At 500 m (1,600 ft) the cockpit canopy was seen to come off as Sieber intended to bail out. He was however instructed by radio to keep trying to shake off the booster but due to severe buffeting he lost orientation. Eventually, the aircraft flipped over and dived vertically into the ground, killing Sieber. It is suspected that Sieber and his aircraft may have broken the sound barrier on the way down.
The cause was explained as a failure of the canopy which may simply not have been properly latched before launch. Many photos and records were altered to hide the fact that a FuG16 radio was in the cockpit and used to order Sieber not to bail out. A recording of the radio transmission disappeared and other material pointing to technical problems being ignored was lost. Excavations of the crash site in 1998 found remains of the troublesome booster.
Lothar Sieber's remains were buried with military honors on 3 March 1945.
Meantime, the booster rockets have been slightly altered to the correct dimensions and the single element made for the 'sled'...
