Congress has been attacking the Modi govt, asking why it did not insist for a sovereign guarantee from the French govt in the Rafale deal
India inked an agreement with Russia in October last year to procure a batch of the missile systems at a cost of Rs 40,000 crore
India last week inked a deal to purchase the S-400 Triumf air defence system from Moscow
By 2021, when the S-400 enters service, India's air defence will be improving
The S-400 missile deal has been an issue of much speculation after the Trump administration's Countering America's Adversaries Through Sanctions Act (CAATSA) law came into effect in January
Only last month, US had used CAATSA to impose sanctions on Chinese entities for the purchase of S-400
Putin's last-minute intervention with PM salvages $5.43 bn pact
India is hoping that President Donald Trump's administration will give it a waiver on the weapons systems which New Delhi sees as a deterrent against China
The delivery of the missile systems, tipped to be over $5 billion, will start 24 months from the signing of the contract
Its integration may turn the missile into a white elephant that could bleed the military down the line; it may also not be effective against the F-16s Pakistan has bought, or China's stealth fighters
With India pressing for delivery of the first S-400 units by 2020, the order must be placed at the latest in October
The deal was signed during Russian President Vladimir Putin's visit to India in October 2016, and negotiations are being conducted on factors like technology transfer and final price
It can destroy incoming hostile aircraft, missiles and even drones at ranges of up to 400 km