Bangladesh Liberation War Important months

March–June

At first, resistance was spontaneous and disorganized, and was not expected to be prolonged. However, when the Pakistani Army cracked down upon the population, resistance grew. The Mukti Bahini became increasingly active. The Pakistani military sought to quell them, but increasing numbers of Bengali soldiers defected to the underground "Bangladesh army". These Bengali units slowly merged into the Mukti Bahini and bolstered their weaponry with supplies from India. Pakistan responded by airlifting in two infantry divisions and reorganising their forces. They also raised paramilitary forces of Razakars, Al-Badrs and Al-Shams (who were mostly members of the Muslim League, Jamaat E Islami and other Islamist groups), as well as other Bengalis who opposed independence, and Bihari Muslims who had settled during the time of partition.

On 17 April 1971, a provisional government was formed in Meherpur district in western Bangladesh bordering India with Sheikh Mujibur Rahman, who was in prison in Pakistan, as President, Syed Nazrul Islam as Acting President, Tajuddin Ahmed as Prime Minister, and General Muhammad Ataul Ghani Osmani as Commander-in-Chief, Bangladesh Forces. As fighting grew between the occupation army and the Bengali Mukti Bahini, an estimated 10 million Bengalis, sought refuge in the Indian states of Assam and West Bengal.

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).

General Osmani had differences of opinion with the Indian leadership regarding the role of the Mukti Bahini in the conflict. Indian leadership initially envisioned Bengali forces to be trained into a small elite guerrilla force of 8,000 members, led by the surviving East Bengal Regiment soldiers operating in small cells around Bangladesh to facilitate the eventual Indian intervention, but the Bangladesh Government in exile and General Osmani favoured the following strategy:

• Bengali conventional force would occupy lodgment areas inside Bangladesh and then Bangladesh government would request international diplomatic recognition and intervention. Initially Mymensingh was picked for this operation, but Gen. Osmani later settled on Sylhet.
• Sending the maximum number to guerrillas inside Bangladesh as soon as possible with the following objectives:
• Increasing Pakistani casualties through raids and ambush.
• Cripple economic activity by hitting power stations, railway lines, storage depots and communication networks.
• Destroy Pakistan army mobility by blowing up bridges/culverts, fuel depots, trains and river crafts.

The strategic objective was to make the Pakistanis spread their forces inside the province, so attacks could be made on isolated Pakistani detachments.

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 conduct guerrilla operations and train fighters. Most of their training camps were situated near the border area and were operated with assistance from India. The 10th Sector was directly placed under the Commander in Chief (C-in-C) General M. A. G. Osmani and included the Naval Commandos and C-in-C's special force. Three brigades (11 Battalions) were raised for conventional warfare; a large guerrilla force (estimated at 100,000) was trained.

Three brigades (8 infantry battalions and 3 artillery batteries) were put into action between July – September During June – July, Mukti Bahini had regrouped across the border with Indian aid through Operation Jackpot and began sending 2000 – 5000 guerrillas across the border, the so-called Moonsoon Offensive, which for various reasons (lack of proper training, supply shortage, lack of a proper support network inside Bangladesh etc.) failed to achieve its objectives. Bengali regular forces also attacked BOPs 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 Dhaka 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.

October–December

Bangladesh conventional forces attacked border outposts. Kamalpur, Belonia and the Battle of Boyra are a few examples. 90 out of 370 BOPs fell to Bengali forces. Guerrilla attacks intensified, as did Pakistani and Razakar reprisals on civilian populations. Pakistani forces were reinforced by eight battalions from West Pakistan. The Bangladeshi independence fighters even managed to temporarily capture airstrips at Lalmonirhat and Shalutikar Both of these were used for flying in supplies and arms from India. Pakistan sent another 5 battalions from West Pakistan as reinforcements.