Answer by Aman Rai:
During Indo-Pak war of 1971,Russia backed India,when west was backing pakistan. Russians actually sent a nuclear warship and two groups of nuclear submarines fitted with an array of ready to fire nuclear warheads, cruisers and destroyers to counter the U.S's seventh fleet and a British warship during the 1971 war with Pakistan.Growing political influence in East Pakistan of Bengalis Pakistan feared of loosing East Pakistan,so they started killing Bengalis on eastern front.This created a potential problem for India as lakhs of refugees wanted to come to India for shelter and food. It was then that India took upon herself the onerous task of liberating East Pakistan from Pakistan's clutches. Alarmed at this threat the Pakistanis soon went to their most important ally(A nation who think itself as the angels of Democracy).Indian Intelligence got input of US seven fleet entering the war zone.The Seventh Fleet, which was then stationed in the Gulf of Tonkin, was led by the 75,000 ton nuclear powered aircraft carrier, the USS Enterprise. The world’s largest warship, it carried more than 70 fighters and bombers. The Seventh Fleet also included the guided missile cruiser USS King, guided missile destroyers USS Decatur, Parsons and Tartar Sam, and a large amphibious assault ship USS Tripoli.Standing between the Indian cities and the American ships was the Indian Navy’s Eastern Fleet led by the 20,000-ton aircraft carrier, Vikrant, with barely 20 light fighter aircraft.Meanwhile, Soviet intelligence reported that a British naval group led by the aircraft carrier Eagle had moved closer to India’s territorial waters. This was perhaps one of the most ironic events in modern history where the Western world’s two leading democracies were threatening the world’s largest democracy in order to protect the perpetrators of the largest genocide since the Holocaust in Nazi Germany. However, India did not panic. It quietly sent Moscow a request to activate a secret provision of the Indo-Soviet security treaty, under which Russia was bound to defend India in case of any external aggression.The British and the Americans had planned a coordinated pincer to intimidate India: while the British ships in the Arabian Sea would target India’s western coast, the Americans would make a dash into the Bay of Bengal in the east where 100,000 Pakistani troops were caught between the advancing Indian troops and the sea.To counter this two-pronged British-American threat, Russia dispatched a nuclear-armed flotilla from Vladivostok on December 13 under the overall command of Admiral Vladimir Kruglyakov, the Commander of the 10th Operative Battle Group (Pacific Fleet).In the way of the American Navy stood the Soviet cruisers, destroyers and atomic submarines equipped with anti-ship missiles. We encircled them and trained our missiles at the Enterprise. We blocked them and did not allow them to close in on Karachi, Chittagong or Dhaka."At this point, the Russians intercepted a communication from the commander of the British carrier battle group, Admiral Dimon Gordon, to the Seventh Fleet commander: “Sir, we are too late. There are the Russian atomic submarines here, and a big collection of battleships.” The British ships fled towards Madagascar while the larger US task force stopped before entering the Bay of Bengal.The Russian manoeuvres clearly helped prevent a direct clash between India and the US-UK combine.