The development of the R-36 missile complex for use with the 8К69 (termed Fractional Orbital Bombardment System in the West, NATO reporting name SS-9 Mod 3) began on April 16, 1962. Such a missile provided some advantages over a conventional ICBM. The structure and design of the fractional orbit bombardment system were similar to a conventional R-36 ICBM system. The main difference from a conventional ICBM was in the design of the re-entry vehicle, which is fitted with a single 2.4 Mt warhead, a de-orbit engine, and a control block. The control system independently uses inertial guidance and a radar altimeter which measure orbit parameters twice, once at the beginning of the orbital trajectory and again just before the firing of engines for de-orbiting. The silo launcher and command point were hardened against a nuclear blast.