A-4 did not have a tendency to form ice, a problem which plagued other early ballistic missiles such as the balloon tank-design SM-65 Atlas which entered US service in 1959. The tanks held of ethyl alcohol and of oxygen. The V-2 was guided by four external rudders on the tail fins, and four internal graphite vanes in the jet stream at the exit of the motor. These 8 control surfaces were controlled by Helmut Hölzer's analog computer, the , via electrical-hydraulic servomotors, based on electrical signals from the gyros. The Siemens Vertikant LEV-3 guidance system consisted of two free gyroscopes (a horizontal for pitch and a vertical with two degrees of freedom for yaw and roll) for lateral stabilization, coupled with a PIGA accelerometer, or the Walter Wolman radio control system, to control engine cutoff at a specified velocity. Other gyroscopic systems used in the A-4 included Kreiselgeräte's SG-66 and SG-70. The V-2 was launched from a pre-surveyed location, so the distance and azimuth to the target were known. Fin 1 of the missile was aligned to the target azimuth. Some later V-2s used "guide beams", radio signals transmitted from the ground, to keep the missile on course, but the first models used a simple analog computer that adjusted the azimuth for the rocket, and the flying distance was controlled by the timing of the engine cut-off, Brennschluss, ground-controlled by a Doppler system or by different types of on-board integrating accelerometers. Thus, range was a function of engine burn time, which ended when a specific velocity was achieved. Just before engine cutoff, thrust was reduced to eight tons, in an effort to avoid any water hammer problems a rapid cutoff could cause. Dr. Friedrich Kirchstein of Siemens of Berlin developed the V-2 radio control for motor-cut-off (). For velocity measurement, Professor Wolman of Dresden created an alternative of his Doppler tracking system in 1940–41, which used a ground signal transponded by the A-4 to measure the velocity of the missile. By 9 February 1942, Peenemünde engineer Gerd had documented the radio interference area of a V-2 as around the "Firing Point", and the first successful A-4 flight on 3 October 1942, used radio control for . Although Hitler commented on 22 September 1943 that "It is a great load off our minds that we have dispensed with the radio guiding-beam; now no opening remains for the British to interfere technically