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June–September

Bangladesh forces command was set up on 11 July, with Col. M. A. G. Osmani as commander-in-chief (C-in-C) with the status of Cabinet Minister, Lt. Col. Abdur Rabb as chief of Staff (COS), Group Captain A. K. Khandker as Deputy Chief of Staff (DCOS) and Major A. R. Chowdhury as Assistant Chief of Staff (ACOS).

Osmani had differences of opinion with the Indian leadership about the role of the Mukti Bahini in the conflict. Indian leadership initially envisioned a well trained force of 8,000 guerrillas, operating in small cells around Bangladesh to facilitate eventual conventional combat. With the Bangladesh government in exile, Osmani favoured a different strategy:

Bangladesh was divided into eleven sectors in July, each with a commander chosen from defected officers of the Pakistani army who joined the Mukti Bahini to lead guerrilla operations. The Mukti Bahini forces were given two to five weeks of training by the Indian army on guerilla warfare. Most of their training camps were near the border area and operated with assistance from India. The 10th Sector was placed under Osmani's command and included the Naval Commandos and C-in-C's special force. Three brigades (eventually 8 battalions) were raised for conventional warfare; a large guerrilla force (estimated at 100,000) was trained.

Five infantry battalions were reformed and positioned along the northern and eastern borders of Bangladesh. Three more battalions were raised, and artillery batteries were formed. During June and July, Mukti Bahini regrouped across the border with Indian aid through Operation Jackpot and began sending 2,000–5,000 guerrillas across the border, the so-called Monsoon Offensive, which for various reasons (lack of proper training, supply shortage, lack of a proper support network inside Bangladesh) failed to achieve its objectives. Bengali regular forces also attacked border outposts in Mymensingh, Comilla and Sylhet, but the results were mixed. Pakistani authorities concluded that they had successfully contained the Monsoon Offensive, which proved a near-accurate observation.

Guerrilla operations, which slackened during the training phase, picked up after August. Economic and military targets in Dacca were attacked. The major success story was Operation Jackpot, in which naval commandos mined and blew up berthed ships in Chittagong, Mongla, Narayanganj and Chandpur on 15 August 1971.