The Indian government has yet to announce a final decision on the purchase of a new air defense system. India may favor the S-400 since its can defend against manned aircraft and some missile threats.

THAAD missile test fire (Picture source: U.S. Missile Defense Agency)

The Terminal High Altitude Area Defense (THAAD) is a key element of the Ballistic Missile Defense System (BMDS) designed to defend U.S. troops, allied forces, population centers, and critical infrastructure. THAAD operates in a unique battle space intercepting both endo- and exo-atmospheric short-to-intermediate range ballistic missiles. This ground-based missile defense system is rapidly deployable with high mobility, providing proven capability to Combatant Commanders world-wide.

THAAD is an interoperable system with other BMDS elements and can accept cues from Aegis, satellites and other external sensors, as well as work in concert with the Patriot/PAC-3. The THAAD (theatre high-altitude area defence) missile system is an easily transportable defensive weapon system to protect against hostile incoming threats such as tactical and theatre ballistic missiles at ranges of 200km and at altitudes up to 150km.