The delivery of the "game-changing" S-400 Triumf air defence missile systems by Russia to India will be delayed by at least two years.

The original timeline stipulated at the time of the signing of the 40,000 Crore ($5.43 Billion) contract on October 5, 2018 required the delivery of five S-400 systems to India between October 2020 and April 2023.

But Russia on February 17 conveyed that the revised deadline would delay delivery to 2025.

"We are about to cross USD 16 Bn amount of deals. Both sides are committed to their timely and successful implementation, including supply of the S-400 best in the world air defence systems by 2025," the Russian Embassy in New Delhi declared in a statement.

The original timeline stipulated at the time of the signing of the 40,000 Crore ($5.43 Billion) contract on October 5, 2018 required the delivery of five S-400 systems to India between October 2020 and April 2023

In July 2019, the Government of India told Parliament that deliveries would be completed by April 2023. "A contract had been signed on 5 October, 2018 for delivery of S-400 system from Russia. The deliveries are likely to be made by April 2023", Minister of State for Defence Shripad Naik stated in a response to a question in the Lok Sabha.

This mega contract was signed during the 19th India-Russia Annual Bilateral Summit in New Delhi on October 5, 2018 in the face of US threats of sanctions for deals with Russia under the Countering America's Adversaries Through Sanctions Act (CAATSA).

Sources disclosed that the payment of the first installment of 15 per cent of the value of the contract was delayed by several months as the two sides took time to work out a payment mechanism to get around the US sanctions regime.

The Russians have so far given repeated public assurances that they would make up the time lost in devising an alternate payments mechanism, and stick to original timelines.

Sources disclosed that the payment of the first installment of 15 per cent of the value of the contract was delayed by several months as the two sides took time to work out a payment mechanism to get around the US sanctions regime

In the backdrop of these assurances, the declaration of delay now has come as a surprise, particularly so as India has been pressing for speeding up the original delivery schedule. This was reiterated as recently as in November 2019 during the meeting of the India-Russia Commission for Military Technical Cooperation which was chaired by the respective Defence Ministers.

After the payment of advance, the subsequent installments are linked to contractual and delivery timelines.

Acquisition of the S-400 is critical to India's military preparedness plans in filling up glaring air defence gaps. It was on account of the critical necessity that even the requirement for offsets (counter-trade obligations) was waived off for Russia. The delay prolongs India's air defence vulnerabilities.

The Russians have so far given repeated public assurances that they would make up the time lost in devising an alternate payments mechanism, and stick to original timelines

Touted as the world's most advanced theatre air defence system, the Russian Almaz-Antey's S-400 is capable of intercepting a wide range of airborne threats up to a range of 400 km. Besides enemy aircraft, unmanned systems and cruise missiles, the system is capable of intercepting even tactical and medium range ballistic missiles.

Along with the Rafale fighter aircraft, the S-400 has repeatedly been termed as "game changer" by the Indian Air Force. The air defence system is equipped with target acquisition radars and a variety of interception missiles to thwart threats at ranges of 120, 200, 250 and 400 km. An S-400 battery can reportedly be armed with up to 128 missiles. The system is highly mobile and meant to be deployed close to the borders.