The SA-4 Ganef (NATO reporting name) or 2K11 Krug is a Soviet and now Russian long range, medium-to-high altitude surface-to-air missile (SAM) system. Development of the Krug ZRK-SD (2K11) air defense system started in 1957. It was first displayed during a parade in Moscow in May 1964. The early version of the Krug entered service in 1965. The first operational deployment version, the Krug-A, entered service in 1967, with extensively modified versions, the Krug-M in 1971 and the Krug-M1 in 1974, which were developed to rectify problems discovered during army service. The missiles are launched with the aid of four solid fuel rocket motors inside boosters attached to the outside of the massive missile. Once they have burned and the missile is aloft, it fires a liquid-fuelled ramjet sustainer engine. Missile guidance is via radio command with a terminal semi-active radar homing phase. Optical tracking is possible for the initial command guidance stage in a heavy ECM environment. The missiles are quite large and unlikely to hit small, maneuverable aircraft like fighter jets unless they are caught unaware.