Bachem Ba 349 B-1 Natter (Viper)

Dr. Erich Bachem's Ba 349 Natter (Viper) was the world's first, manned, vertical-take-off interceptor. The aircraft was an imaginative solution to a desperate problem but World War II ended before the weapon saw combat. Dr. Werner von Baun first proposed the concept in 1939 but the Air Ministry (RLM) rejected it as "unnecessary and unworkable." Bachem, an engineer with the Fieseler works, thought the idea had merit. He tried but failed to generate interest in several different proposals for a rocket interceptor.

During spring 1944, the Allied bombing offensive began taking a serious toll on the German war machine. None of the conventional methods employed by the Luftwaffe to intercept the bombers seemed to work so the service began to explore unconventional means. The RLM Technical Office issued requirements for an inexpensive fighter made of non-essential materials that could defend important targets. Messerschmitt, Junkers, Heinkel, and Erich Bachem submitted proposals but RLM officials remained unenthusiastic about Bachem's design. They chose a more conventional offering from Heinkel but Bachem refused to give up. He sought the support of Reichsführer Heinrich Himmler, head of the SS (Nazi Party security forces). Himmler liked Bachem's proposal and signed an order to build 150 Natters using SS funds. It was now possible that the SS might develop an aircraft beyond the RLM's control so they placed their own order for 50 Natters and announced the official designation, Bachem Ba 349.

Bachem's design was simple and easy to build. Semi-skilled labor could construct one in about 1000 man-hours. The wings were plain rectangular wooden slabs without ailerons, flaps, or other control devices. The cruciform tail consisted of four fins and control surfaces. Deflecting these surfaces in various combinations controlled pitch, yaw, and roll, once the Ba 349 had reached sufficient speed to generate adequate airflow. Aerodynamic control was augmented by guide vanes connected to the four control surfaces. Bachem positioned each vane within the exhaust plume of the main engine, a Walter 109-509A rocket motor. This is the same basic engine used in the Messerschmitt Me 163 Komet (also preserved in the NASM collection). Two liquid fuels combined inside the motor to generate thrust. When T-Stoff (a highly caustic solution of hydrogen peroxide and a stabilizing chemical) mixed with C-Stoff (a hydrazine hydrate/methanol/water mixture), combustion was spontaneous so extreme care was required to handle both chemicals. The Walter motor generated about 1,700 kg (3,740 lb) of thrust but a loaded Ba 349A weighed more than 1,818 kg (4,000 lb) so liftoff required more power.

Bachem got the extra thrust from four Schmidding 109-533 solid-fuel rocket motors that he bolted to the aft fuselage, two per side. Each motor produced 500 kg (1,100 lb) of thrust. At liftoff, all five motors ignited, generating about 3,700 kg (8,140 lb) of thrust. The resulting 1.6 to 1 thrust-to-weight ratio produced acceptable climb performance.

Natter operations were relatively simple and the following account describes a hypothetical mission. A 24 m (79 ft) tower guided the rocket plane during liftoff. The wingtips and lower fin fit inside guide rails to stabilize the aircraft until it cleared the tower. The flight controls remained locked in neutral position until the solid boosters burned out about 10 seconds into the flight. At burnout, explosive bolts blasted away the solids, the flight controls unlocked, and the Natter's 3-axis Patin autopilot began receiving steering commands from the ground via radio. The airplane continued climbing but the pilot could intercede at any time and take full control. Bachem calculated maximum climb rate at 11,563 m (37, 400 ft) meters per minute but flight tests did not confirm this figure.

American daylight bomber formations often approached a target at an altitude of 6,250 m (20,000 ft) to 9,375 m (30,000 ft). After the Natter had climbed even with the formation, the pilot took control, steering his Natter in close. At a range of about 1.6-3.2 kilometers (1-2 miles) from the formation, the Natter pilot jettisoned the nose cone and shotgun style, salvoed all 24 Henschel Hs 217 Föhn unguided rockets.

Rocket fuel would be nearly exhausted by now, so the pilot began to descend. At about 1,400 m (4500 ft), the pilot released his seat harness and fired a ring of explosive bolts to blow off the entire nose section. A parachute simultaneously deployed from the rear fuselage and the sudden deceleration literally threw the pilot from his seat. The pilot activated his own parachute after waiting a safe interval to clear the bits of falling Natter. Ground crews recovered the Walter motor to use again but the airframe was now scrap.

Bachem set up a factory to design and build his dream at Waldsee in the Black Forest. By November 1944, the first Natter was ready for tests configured as a motorless glider. A Heinkel He 111 bomber carried one to 18,000 ft and released it. The pilot found the aircraft easy to control. At 1000 m (3,200 ft), he fired the explosive bolts and the escape sequence worked as designed. A powered vertical launch failed on December 18 because of faulty ground equipment design. On December 22, the aircraft made its first successful launch with the solid fuel boosters only because the Walter motor was not ready. Ten more successful launches followed during the next several months. Early in 1945, the Walter engine arrived and the Natter launched successfully with a complete propulsion system on February 25, 1945, carrying a dummy pilot. The launch proved that the complete flight profile was workable. All went according to plan, including recovery of the pilot dummy and Walter rocket motor.

Now a man had to fly and the first test came on February 28. Oberleutnant Lothar Siebert climbed into a Ba 349A, strapped in, and rocketed off the launch tower. At about 500 m (1600 ft), the Natter shed its canopy and headrest and the aircraft veered off and flew into the ground, killing Siebert. No cause was determined but the ground crew may have failed to lock the canopy and it could have struck the pilot. Despite the tragedy, more pilots volunteered to fly and the Bachem team launched three flights in March.

With the end near, the Germans erected a battery of ten Natters at Kircheim near Stuttgart. Pilots stood alert day after day but no U. S. bombers flew into range. The U. S. Seventh Army overran the site but not before the Germans blew up all ten Natters and their launchers.

It is interesting to speculate about the Natter's potential effectiveness. Realistic flight training was next to impossible using an aircraft that destroyed itself after every flight. However, given the short duration of a typical interception (about 5-10 minutes), and positive ground control for much of the flight, the German could have eased training with a simple ground simulator. Once the German's erected a Natter site, U. S. Army Air Forces strike planners could easily route the bombers out of harm's way. Accuracy of the unguided rocket salvo is also questionable and it was a one-shot opportunity. It is safe to assume that the Bachem Ba 349A Natter was a bad idea from the start and as a bomber interceptor, it was a total failure.

Only two Bachem Natters are known to exist. The Deutsches Museum, Munich, Germany, displays a Ba 349A restored in the colors and markings of one of the unmanned test aircraft. The NASM has the other Natter. U. S. forces captured this artifact at war's end and shipped it to Freeman Field, Indiana, for analysis. The captured equipment number T2-1 was assigned to the Natter and the U. S. Air Force transferred it to the National Air Museum (now NASM) on May 1, 1949.