Pakistan cuts off diplomatic relations with India, initiating the Indo-Pakistani War of 1971.

The Indo-Pakistani War of 1971 was a military confrontation between India and Pakistan that occurred during the liberation war in East Pakistan from 3 December 1971 to the fall of Dacca on 16 December 1971. The war began with preemptive aerial strikes on 11 Indian air stations, which led to the commencement of hostilities with Pakistan and Indian entry into the war of independence in East Pakistan on the side of Bengali nationalist forces. Lasting just 13 days, it is one of the shortest wars in history.

During the war, Indian and Pakistani militaries simultaneously clashed on the eastern and western fronts; the war ended after the Eastern Command of the Pakistan military signed the Instrument of Surrender on 16 December 1971 in Dhaka, marking the formation of East Pakistan as the new nation of Bangladesh. Officially, East Pakistan had earlier called for its secession from the unity of Pakistan on 26 March 1971. Approximately 90,000 to 93,000 Pakistani servicemen were taken prisoner by the Indian Army, which included 79,676 to 81,000 uniformed personnel of the Pakistan Armed Forces, including some Bengali soldiers who had remained loyal to Pakistan. The remaining 10,324 to 12,500 prisoners were civilians, either family members of the military personnel or collaborators. It is estimated that between 300,000 and 3,000,000 civilians were killed in Bangladesh. As a result of the conflict, a further eight to ten million people fled the country to seek refuge in India.

During the 1971 Bangladesh war for independence, members of the Pakistani military and supporting Islamist militias called the Razakars raped between 200,000 and 400,000 Bangladeshi women and girls in a systematic campaign of genocidal rape.

Unlike the 1965 war, the Navy NHQ staffers and commanders of the Pakistan Navy knew very well that the Navy was ill-prepared for the naval conflict with India. The Pakistan Navy was in no condition of fighting an offensive war in deep sea against the Indian Navy, and neither was it in a condition to mount serious defence against Indian Navy’s seaborne encroachment.

In the western theatre of the war, the Indian Navy’s Western Naval Command under Vice Admiral S.N. Kohli, successfully launched a surprise attack on Karachi port on the night of 4/5 December 1971 under the codename Trident. The naval attack involving the Soviet-built Osa missile boats sank the Pakistan Navy’s destroyer PNS Khaibar and minesweeper PNS Muhafiz while PNS Shah Jahan was also badly damaged. Pakistani naval sources reported that about 720 Pakistani sailors were killed or wounded, and Pakistan lost reserve fuel and many commercial ships, thus crippling the Pakistan Navy’s further involvement in the conflict. In retaliation, the Pakistan Navy submarines, Hangor, Mangro, and Shushuk, began their operations to seek out the major Indian warships. On 9 December 1971, Hangor sank INS Khukri, inflicting 194 Indian casualties, and this attack was the first submarine kill since World War II.

The sinking of INS Khukri was followed by another Indian attack on Karachi port on the night of 8/9 December 1971 under the codename Python. A squadron of Indian Navy’s Osa missile boats approached the Karachi port and launched a series of Soviet-acquired Styx missiles, that resulted in further destruction of reserve fuel tanks and the sinking of three Pakistani merchant ships, as well as foreign ships docked in Karachi. The Pakistan Air Force did not attack the Indian Navy ships, and confusion remained the next day when the civilian pilots of Pakistan International, acting as reconnaissance war pilots, misidentified PNS Zulfiqar and the air force attacked its own warship, inflicting major damages and killing several officers on board.

In the eastern theatre of the war, the Indian Eastern Naval Command, under Vice Admiral Nilakanta Krishnan, completely isolated East Pakistan by a naval blockade in the Bay of Bengal, trapping the Eastern Pakistan Navy and eight foreign merchant ships in their ports. From 4 December onwards, the aircraft carrier INS Vikrant was deployed, and its Sea Hawk fighter-bombers attacked many coastal towns in East Pakistan, including Chittagong and Cox’s Bazar. Pakistan countered the threat by sending the submarine PNS Ghazi, which sank en route under mysterious circumstances off Visakhapatnam’s coast.

Due to high number of defections, the Navy relied on deploying the Pakistan Marines – led by Rear Admiral Leslie Mungavin – where they had to conduct riverine operations against the Indian Army, but they too suffered major losses, mainly due to their lack of understanding of expeditionary warfare and the wet terrain of East Pakistan.