In an off-the-record conversation, a senior air force commander uses the word 'game-changer' three times to refer to the Russian S-400 long-range missile system. "The system can knock down anything that flies, at a range of nearly 400 kilometres," he says. In Washington, suspense over a different game-to persuade India from not going ahead with a proposed $4.5 billion (Rs 39,000 crore) buy of five S-400 missile systems-ended with the US Senate and House on July 24 finally passing a modified version of a bill that allows India to buy the Russian weapon system without the threat of US sanctions.

As late as July 21, it appeared India would attract US sanctions under what is called the Countering America's Adversaries Through Sanctions Act (CAATSA). The bill, which came into effect this year, penalises countries doing business with arms firms in Russia, North Korea and Iran. The US state department issued a statement terming the S-400 sale as 'potentially sanctionable activity'. In the end, Indian officials say, it was US defense secretary James Mattis, an ardent proponent of a CAATSA waiver for India, who prevailed over the US state department.

The Modi government's gambit of digging its heels in seems to have paid off. Modifications to Section 231 of CAATSA enable the US president to waive sales like the S-400 to protect US alliances, like the one it has with India. "The deal is almost at a conclusive stage," defence minister Nirmala Sitharaman told the media recently.

It is hard to recall the last time the acquisition of a single weapon system by India became such a huge foreign policy challenge as it has with the S-400. Sitharaman recently said the Indian side had conveyed to the US that India had time-tested relations with Russia, the S-400 deal was being negotiated for several years and that CAATSA was a US law and not a UN law, implying it did not apply to India.

We made it clear that CAATSA was a US law and not a UN law. Negotiations for the (S-400) missiles have been on for several years. - Nirmala Sitharaman, Defence Minister

The CAATSA waiver comes just before India's first '2+2 dialogue' with the US. Secretary of state Mike Pompeo and defense secretary James Mattis will be meeting their Indian counterparts, foreign minister Sushma Swaraj and Sitharaman, in New Delhi on September 8. The missile deal itself is likely to be signed during another important meeting-Prime Minister Modi's summit with Russian president Vladimir Putin in India later this year.

The US is India's largest arms supplier after Russia. US firms have sold India over $10 billion worth of military hardware, mainly aircraft, over the last decade. The IAF operates frontline US aircraft like the C-17 Globemaster, the C-130-J Super Hercules and will soon receive Apache helicopter gunships and Chinook transport helicopters. A key worry among US policymakers is that radar signatures and transmission frequencies of their aircraft being exposed to the S-400 missile system and used by Russia to counter them in other potential conflict zones. India is believed to be working on ways to assuage these concerns. Apart from the game changer it is perceived to be, the IAF sees the S-400 'Triumf' as an absolute necessity and part of its offensive-defence strategy of maintaining a credible deterrence along two fronts with China and Pakistan.

The S-400 is an integrated, highly-mobile system of radars and missiles of different ranges to address multiple threats. "Deploying one weapon system allows you to cover an entire spectrum of aerial threats," a senior IAF officer explains. Its 'Tombstone' radar can acquire up to 300 targets nearly 600 km away. Which means, from their locations in India, the system can peer deep inside Pakistani territory and pick up aircraft as soon as they are airborne. Deployed along the eastern border with China, the missile system can easily monitor fighter jets taking off from airfields along the Tibetan plateau.

The system has four different missiles, from the 400-km range 40N6 which can knock out early warning aircraft, fighter jets and tactical ballistic missiles, to the 100-km range 9M96E which can neutralise manoeuvring targets like air-launched cruise missiles and smart bombs. It is a missile system that is frequently used by Moscow to make a geopolitical statement.

In the mid '90s, the DRDO had briefly considered acquiring the long-range radars of an earlier version, the S-300V. (It finally got the Israeli Swordfish long-range radar.)

The IAF sees in the S-400 an answer to its shrinking fighter strength. It has 33 squadrons against a sanctioned strength of 39.squadrons and even this number is likely to shrink to 19 by 2027 when 14 squadrons of MiG-21, MiG-27 and MiG-29 aircraft are retired. The last batch of 18 Su-30 MKI fighters are rolling off the production lines of HAL's Nashik factory. The only acquisition on the horizon in the short term are 36 Rafales from France to be delivered by 2021. "That's what makes the deployment of the S-400 an absolute necessity," a senior IAF officer says. "The missile will free up our multi-role fighters to do other tasks like air-to-ground missions instead of being tied up in the air superiority role."

A parliamentary standing committee on defence report tabled in the Lok Sabha in March this year called the long-range system a 'high priority requirement' for the IAF.

In his deposition before the standing committee chairman, the IAF's Vice Chief of Air Staff Air Vice Marshal S.B. Deo said the system would 'substantially change our posture, both towards the adversary in the Northern Front as well as the one on the Western Front'.

THE CAATSA CHANGE THAT BENEFITS INDIA: The National Defense Authorisation Act (NDAA) specifying the budgetary spends of the US military has inserted a modified waiver to Section 231 of CAATSA, enabling 'presidential certifications designed to protect US alliances, military operations and sensitive technology; encourage allies and partners to reduce inventory of Russian-produced major defense equipment and advanced conventional weapons'.

The S-400 will sit atop the IAF's pan-India Integrated Command and Control System (IACCS) which aims, for the first time, to provide a comprehensive picture of Indian airspace by linking all ground and airborne sensors and air defence assets into a single grid. An upgrade of IACCS-2 costing some Rs 8,000 crore adding four more nodes in the grid was approved in July 2018. The system will give a composite air situation picture integrating all air force, navy, army and civilian radars. It augments critical gaps in the IAF's air defence umbrella which, after decades of neglect, has acquired a lethal edge. In the 12th plan, the iaf has inducted Akash missile systems, medium- and high-powered radars, low-level lightweight radars, low-level tracking radars, AEW&C and AWACS and Ground-Based Mobile Electronic Intelligence Systems (GBMES) and balloon-based Aerostat radars.

The missile acquisition is also a reaffirmation of India's defence relationship with Russia. Apart from a 20-year ongoing Indo-Russian BrahMos supersonic cruise missile, there are virtually no joint development defence projects between India and Russia. Russia has, in recent years, lost a number of defence contracts to US firms and has watched India replace, in some cases like long-range maritime patrol aircraft for the navy and strategic airlift for the air force, its entire inventory of Soviet hardware with US-made systems. The last batch of Sukhoi Su-30s, part of a 2001 deal to licence-produce 272 of the Russian jets, are now rolling off the production lines at HAL, Nashik. No additional orders are likely. Earlier this year, the MoD pulled out of an Indo-Russian Fifth Generation Fighter Aircraft (FGFA), after investing $295 million and 11 years in the project. A deal to co-produce Kamov Ka-226 helicopters for the three armed forces has been dogged by starting issues. The S-400 could thus be more than just a game-changer if it dodges US sanctions.