India-Russia S-400 defence deal: Know what is it; How does it make US 'angry'

New Delhi:  Russian President Vladimir Putin has arrived in India on his two-day visit and the main focus during the meeting between the two nations will be on the S-400 Triumf air defence missile systems agreement. Here is all you need to know about the USD 5 billion deal. What is S-400? S-400 is a powerful air defence system that can take down aircraft in the sky from the surface itself and is intended to act as a shield against incoming ballistic missiles. It is known as Russia's most advanced long-range surface-to-air missile defence system. An upgraded version of the S-300 systems, the S-400 missile system, manufactured by Almaz-Antey, has been in service in Russia since 2007. How will it help India? India wants to procure the long-range missile systems to tighten its air defence mechanism, particularly along the nearly 4,000-km-long Sino-India border. The powerful missile system can be used to tackle enemies from two fronts. The upgraded missile systems will help combat attacks from the two likeliest quarters China and Pakistan. China was the first foreign buyer to seal a government-to-government deal with Russia in 2014 to procure the lethal missile system and Moscow has already started delivery of an undisclosed number of the S-400 missile systems to Beijing in January 2018. How does it irk US? The purchase will infringe sanctions under the Countering America's Adversaries through Sanctions Act (CAATSA) instituted by the US Congress on arms purchases from Russia in the backdrop of its military intervention in Ukraine and alleged intervention in 2016 presidential elections, but American lawmakers have allowed the possibility of a presidential waiver. There have been indications by New Delhi that it will go ahead with the deal notwithstanding the US sanctions. "India has maintained its sovereignty as regards to its relationship with countries. We shall maintain it in all earnestness," Defence Minister Nirmala Sitharaman told PTI recently when asked whether the US sanctions will hit India's defence ties with Russia. Russia has been one of India's key suppliers of arms and ammunition. Sources had earlier said Modi and Putin would also deliberate on the impact of US sanctions on the import of crude oil from Iran.