Indian Prime Minister Narendra Modi heads to Moscow after approving what’s set to be his nation’s biggest weapons deal with Russia since 2001, reaffirming a military partnership that newer suppliers like the U.S. will find difficult to dislodge.

The S-400 air defense missile systems, which India plans to buy, are among the "crown jewels" of Russia’s defense capability, according to Jon Grevatt, Asia-Pacific defense-industry analyst for IHS Jane’s. The two-day visit starting Dec. 23 will also include a private dinner with Russian President Vladimir Putin and an event at the Kremlin with Russian and Indian chief executives.

"Russia and India have a very strong partnership that the U.S. can only aspire to," said Grevatt. "Sales from America may ebb and flow, but the sales from Russia will remain strong because there are so many ongoing programs between the two countries."

The $150 billion that Modi plans to spend to upgrade his military could be a welcome diversion for Putin, who’s bracing for a second year of recession amid Western sanctions. Although the U.S. emerged as India’s biggest defense supplier last fiscal year, the Asian nation’s links with Russia stretch back to their Soviet-era ties.

David Fuller's view

This is bold of Modi, who is clearly a global player, leading a country that is likely to become the next superpower before 2025. 

I assume price was a factor because the Dollar is currently the world’s strongest currency, while the Ruble has weakened considerably, losing over half its value against the Greenback since the oil price collapse.