With the Allies decimating the Luftwaffe in 1944, desperate measures were thought up to address the issue. Although most of the Luftwaffe commanders pressed for more jet fighters like the Me 262, all sorts of crazy ideas were given the green light for development, typically at the behest of some high-ranking Nazi official.
The problems were many. Jet engines of the era had serious problems throttling up during takeoff and landing, so airbases were death traps. Once in the air things got much better, but attempting to target a plane travelling 200 or more miles an hour slower was tremendously difficult. This wasn't too much of a problem for the Luftwaffe's cadre of experten pilots, but as the allies thinned their ranks the jets were being flown by "green" pilots who were completely ineffective. No amount of Me 262's would solve this problem, some other solution was needed.
Various efforts had been underway to develop missiles for this purpose, but invariably problems with the guidance systems prevented these from seeing widespread use. Fitting a pilot to the top seemed like the only solution, which the Luftwaffe requested in early 1944. A number of simple designs were proposed, most using a prone pilot to reduce frontal area. The front runner for the design was initially a Heinkel design that took off from a rail and landed on a skid like the Me 163 Komet.
Erich Bachem's BP20 was a warmed-over design from when he worked at Fieseler, but considerably more radical than the other offerings. It was built using glued and screwed wooden parts with an armored cockpit, powered by a Walter 509A-2 rocket, similar to the one in the Me 163. Four strap-on Schmidding rockets were used for launch, providing a combined thrust of 4,800kg (10,582lb) for 10 seconds before they were jettisoned. The plane rode up a rail for the first 80 feet or so, by which time it was going fast enough for the flight controls to keep it flying straight.
The plane took off and was guided almost to the bomber's altitude using radio control from the ground, with the pilot taking control right at the end to point the nose in the right direction and pull the trigger. This fired 24 R4M rockets out of the nose of the plane, at which point it flew up and over the bombers. After running out of fuel the plane would then be used to ram the tail of a bomber, with the pilot ejecting just before impact to parachute to the ground.
Needless to say many thought the idea was crazy and rejected it out of hand. The design was in fact much more reasonable than any of the others in one aspect — they all required the non-existent pilots to actually fly the plane into a landing. After some political wrangling Bachem's design caught the eye of Heinrich Himmler at the SS. Suddenly, one day later, it was the winner of the design contest. The Luftwaffe nevertheless managed to include some minor redesigns to try to save as much of the plane as possible, as well as eliminating the ramming attack.
The resulting tiny plane was fired up a 50 foot wooden pole with the help of four solid fuel rockets, at the end of which it was already going fast enough for its control surfaces to work. The solids burned out after 12 seconds, at which point the Walter rocket was long up to full thrust. The mission now had the plane guided to a point in front and above the bombers, where the pilot would turn off the autopilot, and push over for a gliding attack. After firing its armament of rockets it continued gliding down at high speed to about 3,000m, at which point the plane "broke" when a large parachute opened at the rear of the plane, popping off the nose section and the pilot with it. Both would land under their separate parachutes, and only the cockpit and wooden wings went to waste.
Perhaps even more amazing than the design itself was the fact that it was actually built and tested. This was no small feat due to the incredible secrecy the SS placed on the project. After building wind-tunnel models early in the program, they were shipped off for testing and the only results returned to the Bachem designers were that it would be "satisfactory" up to speeds of about 685mph.
Full sized models were then completed and started flight testing in November 1944. The initial versions didn't include an engine, and were towed in the air by a Heinkel He 111 bombers for glider testing. Others were equipped with extra solid motors for launch and autopilot tests. All of these went well, but during testing it was shown that any attempt to re-use the engine was hopeless, the landing speed was simply too high.
Construction of the production Ba 349A models had already started in October,and fifteen were launched over the next few months. Each launch resulted in some small modification to the design, and eventually these were collected into a "Mark 2" version which started testing in January.
In February the SS funders decided that the program was not going fast enough, and demanded a manned launch of a Mark 2 later that month. Things went well at first, but at 100m the cockpit cover pulled off. The plane continued climbing normally for a time, but at about 600m it suddenly turned over and flew directly into the ground, with the pilot still inside. Wisely, unmanned testing was continued.
US forces overran the factory at Waldsee in April, but small numbers of Bachem staff had moved and taken the remaining ten B models with them. Soon the US had caught up with them again, and six of the ten were burnt. The remaining four are now found in various aviation museums.
Several sources claim that an operational unit of Natters was set up by volunteers in Kirchheim, but didn't carry out any operations. The accuracy of this story is unclear.