The first such SAM project was the Enzian (“Gentian”) missile – the first to use a radio controlled guidance system. It was essentially the unmanned version of the Me-163 manned rocket interceptor but instead of a pilot and two autocannons (20mm or 30mm) carried a 500kg HE warhead.
The basic idea behind the Enzian design was that the missile would fly just in front of the target and then detonate its heavy warhead, in the hope of bringing down not one, but several bombers at once. The lethal radius for this warhead was estimated at 45m.
With no human pilot on board, and thus no need to limit takeoff acceleration, the rocket could use solid fuel boosters reducing the amount of liquid fuel needed for the rest of the climb by the sustainer jet engine.
The result, even with the heavy warhead, was that a much smaller airframe was needed to carry the required fuel – so it could be portable and launched from a modified 88 mm gun mounting. Thus making it easy to transport to the best area for attacking the Allied bomber formation.
The design made as much use of wood as possible, due to the dire need to conserve other “strategic” materials in the rapidly deteriorating war situation.
The Achilles heel of Enzian (which ultimately led to the cancellation of the whole project) was its highly complicated guidance system. Other German SAM were high-speed (supersonic) designs that could be flown directly at their target along the line of sight, which is fairly straightforward even for an inexperienced operator on the ground.
The Enzian was a “low-speed” (subsonic) missile so its operator had to fly the missile into the close proximity of the bombers, then cut the engine and let it glide. Hence, Enzian would instead be approaching its target from somewhere in front, which is considerably harder for the operator and made necessary terminal guidance corrections all but impossible.
Several solutions have been proposed, including an onboard radar, proximity fuse and even an infrared homing system. None produced satisfactory results and, to make things worse, there were problems with availability of engines, so on January 17th, 1945 the Enzian project was canceled.