Prior to Bangladesh Liberation War in 1971, India had no plans for large scale military action in East Pakistan. Since the Sino-Indian War of 1962, the primary objective of the Indian Army Eastern Command was the defence of the Indian northern and eastern borders, defending the "Shiliguri Corridor", and on combating insurgencies raging in Mizoram, Nagaland, Manipur and the Naxalites in West Bengal.
Since 1948 bulk of the Pakistani armed forces were stationed in West Pakistan and the strategic role of the forces in East Pakistan was to hold out until Pakistan defeated India in the west. The Pakistan Army Eastern Command had planned to defend Dhaka until the last by ultimately concentrating their forces along the "Dhaka Bowl", the area surrounded by the rivers Jamuna, Padma and Meghna.
Indian Eastern Command deployments 1971
The Indian army kept parity with Pakistani forces stationed in East Pakistan since 1965, and in 1971 one armoured brigade and one infantry division was deployed in West Bengal. Other Eastern Command units were deployed in Mizoram, Manipur, and Nagaland. Eastern command had 4 administrative units: the Bengal Area corps (the 9th division and other units), the XXXIII corps (3rd armoured brigade, 17th, 27th, 6th and 20th Mountain divisions) guarding the Shiliguri corridor, as well as ensuring security of Sikkim and Bhutan if needed, the 101st Communication Zone (no combat units, an administrative unit which operated in the area between the XXXIII and IV corps), while the IV corps (2nd, 5th, 23rd, 57th and 8th Mountain divisions) ensured the security of Assam, Arunachal, Monipur, Mizoram, Tripura and Nagaland.
April 1971: Indian Intervention in Bangladesh? The main reason Maj. Gen. Rao Farman Ali and Lt. Gen. Sahabzada Yaqub Khan had opposed military action against Bengali civilians was the fear of an Indian attack, which the Pakistan army was woefully unprepared to meet in March 1971. The 14th infantry division with its brigades posted at Comilla (53rd), Dhaka (57th), Rangpur (23rd) and Jessore (107th) was the only Pakistani unit in East Pakistan prior to March 1971. The issue of direct military intervention was discussed between the Indian military and political leadership in April 1971. Although some Indian officers expected early intervention, Indian army command decided against immediate intervention, and concluded that a full attack could only take place after 15 November at the earliest, and only after deliberate and extensive preparations. Indian Army Eastern Command took over responsibility for East Pakistan operations on 29 April, and on 15 May launched Operation Jackpot, a full-fledged operation to arm, train, equip, supply and advice the Mukti Bahini fighters engaged in guerrilla warfare against the Pakistan armed forces.
Indian Army Eastern Command draft plan: May 1971
Indian Eastern Command began drafting an operational plan for military action in Bangladesh from May 1971. Indian planners assumed that Pakistani army would try to defend the whole of the province to prevent Mukti Bahini from establishing the government inside Bangladesh. The main objectives of the May draft plan were:
The capture of Dhaka was the final goal. A winter campaign would reduce the chance of Chinese intervention as passes over the Himalayas would be snowed shut and the ground in Bangladesh would be firm and most favourable for armour and mechanised movements. Some troops deployed on the Chinese border can be used in Bangladesh. October – April period was the best time to launch an offensive, while the Monsoon rains (May – September) turned the country into a morass. Axis of advance should aim to isolate and bypass Pakistani forces – which meant a minimum superiority in numbers was needed. Fortified positions should be bypassed. Subsidiary objectives should be picked to occupy communication centres and destroy Pakistani command and control ability. Preliminary operations (by Mukti Bahini and then Indian forces) should aim to draw the Pakistani forces near the border, so key areas in the interior are left undefended.
Proposed axis of advance
Eastern Command had concluded that The major rivers divided Bangladesh into 4 sectors:
North – Western Sector (Pakistani designation Northern Sector): The area north of the Padma and west of the Jamuna river. Bogra was the main communication hub and the sector is connected to the western sector through the Hardinge Bridge. The Shiliguri corridor, which is vital for road and rail communication with Eastern India, borders the northern tip of this sector.