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 8 tons, in an effort to avoid any water hammer problems a rapid cutoff could cause.