Key point: Moscow is eager to sell (and use) the S-400 both to gain leverage and to threaten its rivals aircraft.
The S-400 is one of the most controversial missiles in the world currently. The United States has imposed economic sanctions on countries simply for buying the system, but many of the world’s powers are interested in it, with India signing deals in September 2018 and China in April 2018. But what exactly makes the S-400 such a hot ticket item in the world today? How did it evolve from the earlier S-300?
The S-300 began development in the 1960s as a follow-up to a multitude of prior surface-to-air missile (SAM) systems. The primary missile it planned to replace is the S-75 (SA-2) missile system, which was famously used against the U-2 spy plane and deployed in Cuba and Vietnam. The missile underwent testing in the 1970s and entered service in 1978.
The primary improvement of the S-300 compared to earlier systems would be the ability to be multichannel—to utilize multiple guidance beams to guide missiles to different targets simultaneously. The earlier S-25 system was also multichannel, but it was extremely heavy and only deployed in stationary mounts. The American SAM-D (which would become the MIM-104 Patriot) was the first American land-based SAM with multichannel technology; it entered service three years later in 1981.
The main customer for the new missile was the Soviet PVO or air defense forces. They adopted the first version of the S-300, the S-300PT. All “P” missiles were meant to be to be for the PVO. The S-300PT involved a towable TEL (Transporter, Erector, Launcher) and towable radar that relied on heavy trucks to reposition. The set also included a fire control system. This was good enough for relatively stationary PVO duties but was not an ideal solution.