Despite US opposition and the prospect of sanctions under the Countering America's Adversaries Through Sanctions Act, India signed a 5.43 billion dollar agreement with Russia for the S-400 Triumf missile system in October 2018.
The S-400 Triumf Missile System has the following features:
The S-400 Triumf is a Russian mobile surface-to-air missile system (SAM). It is the world's most hazardous operationally deployed modern long-range SAM (MLR SAM), with the US-developed Terminal High Altitude Area Defense system trailing far behind (THAAD).
Within a range of 400 kilometres and at altitudes of up to 30 kilometres, the system can engage all forms of aerial targets, including aircraft, unmanned aerial vehicles (UAVs), and ballistic and cruise missiles.
The device can track 100 targets in the air and engage six of them at once.
Importance for India:
China is also buying the system, according to India. China and Russia reached an agreement in 2015 to buy six battalions of the system. It was first delivered in January of this year.
The S-400 system's acquisition by China has been dubbed a "game changer" in the region. Its usefulness against India, however, is limited.
In a two-front battle, India's purchase is critical in countering strikes, including even high-end F-35 US fighter planes.