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Wing: Cantilever mid-wing monoplane. Single-spar wooden wing with a continuous box spar. Each wing half still consists of five ribs and plywood skinning. No ailerons.
Fuselage: Split-frame fuselage in wooden monocoque construction. Plexiglas nose cone. The forward fuselage section up to the cockpit and the rear fuselage section with engine and control surfaces are jettisonable. Parachute compartment for the tail in the rear fuselage.
Elevator: Cantilevered cruciform empennage. Wooden construction with plywood-covered fins and fabric-covered control surfaces. All four empennage surfaces are equipped with control surfaces. Elevator with differential action for lateral control. Additional surfaces for the horizontal stabilizer during takeoff, jettisonable. Additional jet rudders behind the exhaust nozzle.
Landing gear: No landing gear, as it is a disposable component and launches from the gun carriage.
Wingtips and lower vertical stabilizer reinforced with fittings for the gun carriage.
Engine: One Walter HWK 109-559 liquid rocket with 1 x 1,700 kp thrust at full throttle, adjustable to a minimum thrust of 150 kp.
One fuel tank each for T-Stoff (400 liters) and C-Stoff (190 liters) in the fuselage. Four Schmidding 109-533 solid-fuel booster rockets with 4 x 1,200 kp thrust for 10 seconds. Jettisonable after burning out.
Crew: One pilot in an enclosed cockpit. Armored plates in front of and behind the seat, and armored glass on the windshield. Jettisonable nose section for parachute jump.

Designation BP-20. This design was selected for development and given the name Bachem
Ba 349 "Natter".

Bachem Ba 349 "Natter"
In August 1944, project work began on the
"Natter". The subsequent development was under the direct direction of Erich Bachem. However, H. Bethbeder, a skilled Dutch designer, was also significantly involved in the design.

Even during the project work, a combination of aircraft and missile as a salvage vehicle was decided upon. Accordingly, the unusual appearance of the cantilever mid-wing monoplane with its short stub wings was a key feature. To effectively combat the heavily armored enemy bombers, the entire nose section was designed as a missile battery. The pilot's seat followed, then the fuel tanks, and at the rear, the Walter liquid rocket. The rocket battery, covered by a Plexiglas canopy shaped like a nose cone, contained either 24 or 34 rockets, depending on the type of projectiles used, housed in hexagonal or square frames. After the rockets were launched, the aircraft's center of gravity shifted so dramatically that it was no longer airworthy.
Rescuing the pilot at high speeds presented particular challenges. To arrive at a feasible solution, a separation of the nose cone was planned. After separation, the main parachute was to pull the pilot's seat backward and simultaneously retrieve the most valuable equipment in the cockpit. Since, in the context of total war, even the "Natter" could not be used entirely as a waste aircraft, the rear fuselage section with engine and control organs was also designed to be detachable. The rescue of these valuable parts was also to be accomplished by a parachute, which was located in a box on the right side of the rear fuselage. The deployment of the "Natter" was planned as follows: launch from a 10-meter-high pole mount, which stood almost vertically in the launch position, but could be laid flat on the ground for the assembly of the Ba 349 "Natter," which was guided in rails with its wingtips and vertically downward-pointing vertical fin.
Four Schmidding powder rockets, which were suspended from the rear fuselage sides and could be jettisoned, served as launch aids.
Together with the main engine, they provided a total launch thrust of 6,500 kp for approximately ten seconds. This time was sufficient to bring the aircraft to an altitude of 1000 m.
Although the initial acceleration was only 2.2 g, an automatically controlled takeoff was chosen to reduce the physical strain on the pilot. It was carried out by an autopilot, which could be controlled from the ground by a beam guidance system. In this way, the aircraft was guided to within about 1.5 km of the target, at which point the pilot took over control to execute the final target maneuvers manually. During the approach, the pilot was protected from the front by an armored plate behind the missile battery and from the rear by a second armored plate behind his seat, while the small frontal area of ​​the "Natter" further hampered any defense. Once in the launch position, the pilot was to jettison the Plexiglas nose cone and fire the missile battery. At the same time, the bow separated, the pilot was pulled outwards, the The rear fuselage detached, and both it and the pilot floated down by parachute. Since the rear fuselage, along with the engine and control components, could be completely installed in a new aircraft, the loss of the remaining parts was not significant. The entire airframe was made of wood. Production was organized so that it was manufactured in various and geographically separate factories, with final assembly taking place at the Bachem plant by semi-skilled workers. For small production runs, a labor requirement of only 1,000 hours per "Natter" was determined for the airframe and engine. Fifty aircraft were planned for the entire unmanned aircraft test program: ten each for testing flight characteristics, investigating vertical takeoff, solving pilot rescue and aircraft recovery problems, for trials with integrated controls, and finally, for testing the overall procedure. The first manned vertical takeoffs were planned to begin with aircraft number 51. However, the actual testing procedure deviated somewhat from this plan. The first six aircraft were used to test flight characteristics at the Heuberg airfield, where manned "Nattern" aircraft were towed aloft by Fleinkel He 111s. Testing was carried out either in tow under the carrier aircraft or in Mistel tow with subsequent release and free flight.

The trials took place at altitudes up to 5,500 m, during which good stability characteristics were observed during the subsequent steep glide at speeds between 200 and 700 km/h. The first vertical takeoff aircraft was mounted on its launch ramp on December 18, 1944. Its propulsion consisted solely of solid-fuel rocket boosters. Since the launch cable was not adequately protected against the hot combustion gases, the aircraft did not take off. Four days later, on December 22, 1944, the second aircraft lifted off from its launch pad to a height of 800 m and disappeared into the clouds. This attempt was successfully repeated with 10 further prototypes up to an altitude of 3000 m. It became apparent that after the release of the launch rockets, the center of gravity shifted so significantly that considerable stabilization difficulties arose. The countermeasures consisted of increasing the size of the elevator flaps by an additional 1 m, thereby increasing the wingspan of the horizontal stabilizer to 4.5 m. These additional surfaces were automatically jettisoned when the launch rockets were released. Subsequently, testing began with the Walter engines installed. It became apparent that the low speed of 50 to 60 km/h upon leaving the launch ramp resulted in far too little control pressure. For this reason, jet rudders were installed behind the nozzle, which could be controlled analogously to the other rudders. To prevent premature burning of these small metal surfaces, they were cooled for 30 seconds by a small jet of water. On February 25, 1945, the first launch took place, with all individual procedures completed. A dummy served as the "pilot." The test proceeded according to plan; the nose section separated, the dummy floated down by parachute, and the remaining fuselage with the engine also landed almost undamaged. Following this, the RLM (Reich Air Ministry) immediately demanded a launch with a manned aircraft. This test phase was only planned after the automatic control system had also been tested. Although the detailed investigations by Prof. Dr.

Ruff of the DVL had shown that the average acceleration of 2.2 g during takeoff and climb should be quite tolerable for the pilot, this automatic control system had been recommended due to the acoustic stress during takeoff. Nevertheless, at the end of February 1945, the RLM issued the order for a manned vertical takeoff, for which they provided their own pilot, First Lieutenant Lothar Siebert. This attempt failed. The "Natter," piloted by Siebert, climbed normally to an altitude of 500 m, then the cockpit canopy flew off, the aircraft flipped onto its back and disappeared into a high-speed horizontal flight. About a minute later, it exploded and was completely destroyed. The cause of the accident was definitively determined to be the flying off of the canopy, which had probably been damaged during transport and to which the pilot's headrest was attached. The pilot's head must have been jerked backward, causing him to either lose consciousness or immediately suffer a broken neck. Nevertheless, the trials continued until April 1945. A total of 36 aircraft were built, of which 22 trials were launched, four of them manned. Of the remaining 14, ten were destroyed, three fell into American hands and one into Russian hands. The latter was a prototype that had been sent to an alternative facility in Thuringia. The majority of the "Natter" aircraft built were of the Ba 349 A type, however, one or two others were also produced.Ba 349 B among them.

Ba 349 A
While the "Natter" project, the BP-20, was intended to use a Walter HWK 109-559 A engine with 1,500 kgp of thrust, which could be throttled down to a minimum thrust of 300 kg, the production version, designated Ba 349 A "Natter," received the improved Walter HWK 109-559 engine, a direct derivative of the HWK 109-509. The HWK 109-559 had a maximum thrust of 1,700 kgp and a minimum thrust that could be throttled down to 150 kgp.


Ba 349 B
The Ba 349 B was equipped with an improved Walter FIWK 109-509 D hot-rocket engine. This engine, with a maximum thrust of 2000 kp, which could be throttled down to 400 kp, had a so-called cruise combustion chamber as a secondary element, which generated additional thrust sufficient for level flight at a certain altitude. With this engine, the flight time under thrust was increased from two minutes to 4.36 minutes. Airframe-wise, the Ba 349 B was identical to the Ba 349 A, except for minor improvements. Only a single aircraft could be launched.