Wasserfall (‘Waterfall’) was essentially a SAM version of the V-2 (A4) missile, sharing the same general layout and shaping. Since the missile had to fly only to the altitudes of the attacking bombers, and needed a far smaller warhead to destroy these, it could be much smaller than the V-2, about one-fourth the size.
The final specifications of 2 November 1942 called for an interceptor missile with a top speed of Mach 2, able to hit airborne targets flying at up to 900 kph at 5 to 20 km altitude within a radius of 50 km. First versions were to use radio command guidance, to be followed by a self-guiding radar system in later models.
Unlike the V-2, Wasserfall was designed to stand ready for periods of up to a month and fire on command (and thus had to use a very different fuel). Guidance was to be a simple radio control manual command to line of sight (MCLOS) system for use against daytime targets.
The missile operator was mounted beside a chair on a framework that allowed the operator to tilt back to easily look at targets above him, rotating as needed to keep the target in sight.
Night-time use was considerably more complex because neither the target nor the missile would be easily visible. For this role a new system known as Rheinland was under development. Rheinland used a radar unit for tracking the target and a transponder in the missile for locating it in flight.
A simple analog computer guided the missile into the tracking radar beam as soon as possible after launch, using a radio direction finder and the transponder to locate it. Once it entered the radar beam the transponder responded to the radar signals and created a strong blip on the display. The operated then used the joystick to guide the missile so that the blips overlapped.
The original design had called for a 100 kilograms warhead, but because of accuracy concerns it was replaced with a much larger one of 306 kilograms, based on a liquid explosive.
The idea was to create a large blast area effect amidst the enemy bomber stream, which would conceivably bring down several airplanes for each missile deployed. For daytime use the operator would detonate the warhead by remote control.
An arguably revolutionary weapon, Wasserfall required considerable development work, which was not completed before the end of the war. After the first successful firing on March 8th, 1944, three trial launches were completed by the end of June 1944. A launch on January 8, 1945 was a failure, with the engine “fizzling” and launching the missile to only 7 km of altitude at subsonic speeds.
Thirty-five Wasserfall trial firings had been completed by the time Peenemünde was evacuated on February 17, 1945.
Wasserfall was arguably the closest design to the modern SAM systems. So it is no surprise that it became the most influential SAM developed by Nazi Germany. It was produced in the USA as the Hermes surface-to-surface missile, in the USSR as the R-101, and in France as the R.04. In Russia it also became the starting point for the (in)famous R-11/R-17 Scud surface-to-surface missile.