The US is on the horns of a dilemma on India’s $5 billion deal with Russia for purchase of S-400 ‘Triumf’ surface-to-air missile systems. Zoe Stanley Lockman, an assoc research fellow specialising in defence at Singapore-based NTU, said, “The S-400 range would enable India to track aircraft beyond its borders, making it a valuable asset as the People’s Liberation Army Air Force extends its training and deployments closer to Indian territory.”