The third war between India and Pakistan took place between November 22 (when the Indian's began providing active artillery support to the separatists) and Dec 17, 1971.
The origins of the third Indo-Pakistani conflict (1971) were different from the previous conflicts. The Pakistani failure to accommodate demands for autonomy in East Pakistan in 1970 led to secessionist demands in 1971. In March 1971, Pakistan's armed forces launched a fierce campaign to suppress the resistance movement that had emerged but encountered unexpected mass defections among East Pakistani soldiers and police. The Pakistani forces regrouped and reasserted their authority over most of East Pakistan by May.
As a result of these military actions, thousands of East Pakistanis died at the hands of the Pakistani army. Resistance fighters and nearly 10 million refugees fled to sanctuary in West Bengal, the adjacent Indian state. By midsummer, the Indian leadership, in the absence of a political solution to the East Pakistan crisis, had fashioned a strategy designed to assist the establishment of the independent nation of Bangladesh. As part of this strategy, in August 1971, India signed a twenty-year Treaty of Peace, Friendship, and Cooperation with the Soviet Union. One of the treaty's clauses implied that each nation was expected to come to the assistance of the other in the event of a threat to national security such as that occurring in the 1965 war with Pakistan. Simultaneously, India organized, trained, and provided sanctuary to the Mukti Bahini (meaning Liberation Force in Bengali), the East Pakistani armed resistance fighters.
Unable to deter India's activities in the eastern sector, on December 3, 1971, Pakistan launched an air attack in the western sector on a number of Indian airfields, including Ambala in Haryana, Amritsar in Punjab, and Udhampur in Jammu and Kashmir. The attacks did not succeed in inflicting substantial damage. The Indian air force retaliated the next day and quickly achieved air superiority. On the ground, the strategy in the eastern sector marked a significant departure from previous Indian battle plans and tactics, which had emphasized set-piece battles and slow advances. The strategy adopted was a swift, three-pronged assault of nine infantry divisions with attached armored units and close air support that rapidly converged on Dhaka, the capital of East Pakistan. Lieutenant General Sagat Singh, who commanded the eighth, twenty-third, and fifty-seventh divisions, led the Indian thrust into East Pakistan. As these forces attacked Pakistani formations, the Indian air force rapidly destroyed the small air contingent in East Pakistan and put the Dhaka airfield out of commission. In the meantime, the Indian navy effectively blockaded East Pakistan. Dhaka fell to combined Indian and Mukti Bahini forces on December 16, bringing a quick end to the war.
Action in the western sector was divided into four segments, from the cease-fire line in Jammu and Kashmir to the marshes of the Rann of Kutch in northwestern Gujarat. On the evening of December 3, the Pakistani army launched ground operations in Kashmir and Punjab. It also started an armored operation in Rajasthan. In Kashmir, the operations were concentrated on two key points, Punch and Chhamb. The Chhamb area witnessed a particularly intense battle where the Pakistanis forced the Indians to withdraw from their positions. In other parts of Kashmir, the Indians made some small gains along the cease-fire line. The major Indian counteroffensive came in the Sialkot-Shakargarh area south and west of Chhamb. There, two Pakistani tank regiments, equipped with United States-made Patton tanks, confronted the Indian First Armored Corps, which had British Centurion tanks. In what proved to be the largest tank battle of the war, both sides suffered considerable casualties.
Within hours of outbreak of hostilities, the Indian Missile Boat Group was ordered to execute operation Trident, the code name for the first attack on Karachi. The task group consisting of three OSA class missile boats, escorted by two Kamorta class anti-submarine patrol vessels, regrouped off Okha and charged towards Karachi. At 2150 hrs on December 4, the task group was 70 nautical miles south-west of Karachi. Soon thereafter, the task group detected patrolling Pakistani naval ships on their sensors. The deadly missiles were heading towards their targets which were soon hit. PNS Khyber, a destroyer and PNS Muhafiz, a minesweeper were sunk. Another Pakistani destroyer Shajehan was badly damaged. The fuel storage tanks at Karachi harbour were set ablaze, causing heavy loss. Operation Trident was a thundering success with no damage to any of the ships of the Indian Naval Task Group, which returned safely. Operation Trident had introduced to the war, the first ever ship launched missiles in the region.
Enthused by the success of this attack, the Indian Navy planned another offensive operation, code named Python. The continued presence of the Indian Navy's larger ships is the area gave enough indication to the Pakistani naval authorities that more offensive operations were in the offing. The Pak aerial surveillance was stepped up and their ships attempted to outsmart the Indian Navy by mingling with merchant shipping. Notwithstanding these measures by the Pakistanis, operation Python was launched on the night on December 8 and 9, 1971. Despite bad weather and rough seas, the task group consisting of missile boat Vinash and two multipurpose frigates, executed the attack with razor sharp precision. INS Vinash approached close to the Karachi coast and fired four missiles. The first missile struck the fuel tanks at the Keamari Oil Farm. The other three missiles hit the merchant tankers Harmattan, Gulf Star and the Pakistani naval tanker Dacca. More than 50 percent of the total fuel requirement of the Karachi zone was reported to have been blown up. Operation Python was another great success.Though the Indian conduct of the land war on the western front was somewhat timid, the role of the Indian air force was both extensive and daring. During the fourteen-day war, the air force's Western Command conducted some 4,000 sorties. There was little retaliation by Pakistan's air force, partly because of the paucity of non-Bengali technical personnel. Additionally, this lack of retaliation reflected the deliberate decision of the Pakistan Air Force headquarters to conserve its forces because of heavy losses incurred in the early days of the war.