On 26 March Sheikh Mujibur Rahman was taken prisoner by the Pakistan army. At about the same time, Major ziaur rahman announced Bangladesh's independence on behalf of Sheikh Mujib from Kalurghat radio station at Chittagong.
There were spontaneous uprisings throughout Bangladesh following the call of independence. These uprisings were participated by government officials, political activists, students, workers, peasants, professionals and members of the public. After initial resistance, many freedom fighters crossed over into Indian territory to have safe sanctuary, due mainly to the enemy's overwhelming superiority of trained soldiers and modern weapons. The scattered and temporarily retreating rudimentary liberation forces were soon brought under a unified command.
On 4 April, the senior officers of the liberation army assembled at the headquarters of 2nd East Bengal at Teliapara, a semi hilly area covered by tea gardens where Colonel MAG Osmany, Lieutenant Colonel Abdur Rob, Lieutenant Colonel Salahuddin Mohammad Reja, Major Kazi Nuruzzaman, Major khaled mosharraf , Major Nurul Islam, Major Shafat Jamil, Major Mainul Hossain Chowdhury and others were present. In this meeting four senior commanders were entrusted with the responsibility of operational areas. Sylhet-Brahmanbaria area was placed under the command of Major Shafiullah. Comilla-Noakhali area was given to Major Khaled Mosharraf while Chittagong-Chittagong Hill Tracts was given to Major Ziaur Rahman. Kushtia-Jessore area was placed under command of Major Abu Osman Chowdhury. In the meeting the organisational concept of the freedom fighter forces and the command structure were chalked out. Colonel MAG Osmany was to command the liberation forces, later named as mukti bahini .
An exile government called the People's Republic of Bangladesh alias mujibnagar government headed by tajuddin ahmed was formed on 10 April. On the next day Tajuddin Ahmed announced the names of three more regional commanders. Captain Newazish for Rangpur region, Major Najmul Haque for Dinajpur-Rajshahi-Pabna and Major Jalil for Barisal-Patuakhali region. All these regions were later named as sectors. All of Bangladesh was divided into eleven such sectors and different sub-sectors for operational purposes during the Sector Commander's conference held from 10 to 17 July 1971.
On 27 March, Prime Minister of India Mrs. Indira Gandhi expressed full support of her government to the freedom struggle of the Bengalis. Indian Border Security Force (BSF) opened Bangladesh-India border to allow the tortured and panick stricken Bengalis to have safe shelter in India. The governments of West Bengal, Bihar, Assam, Meghalaya and Tripura established refugee camps along the border. These camps became ready ground for recruitment of the freedom fighters. The students, peasants, workers and political activists joined the Mukti Bahini with high spirit to liberate Bangladesh from the Pakistan army. They were given training on tactics and the use of arms and explosives. On completion of training, they were posted to different sectors to fight the enemy. The headquarters of the Bangladesh Forces was established at 8 Theatre Road, Calcutta which started functioning from 12 April 1971. Lieutenant Colonel M A Rab and Group Captain A K Khandaker were appointed as Chief of Staff and Deputy Chief of Staff respectively.
Besides Mukti Bahini, many other bahinis were organised inside Bangladesh at different places to fight Pakistan Army. These Bahinis included Kader Bahini of Tangail, Latif Mirza Bahini of Sirajganj, Akbar Hossain Bahini of Jhinaidah, Hemayet Bahini of Faridpur, Quddus Molla and Gafur Bahini of Barisal, Afsar Bahini of Mymensingh and Aftab Bahini of Mymensingh. A crack platoon consisting of daring youths operated most valiantly in Dhaka city as well. These bahinis were established as a local force based on their own strength taking part in a number of battles with the occupation army. Siraj Sikdar, leader of Sorbohara Party, also organised his force in Barisal. Another Bahini named as Mujib Bahini was organised in India with the active assistance of Major General Oban of the Indian army an expert on guerilla warfare. Mujib Bahini was trained at Dehradun. Student League leaders sheikh fazlul haq mani , Tofael Ahmed, Abdur Razzak and Sirajul Alam Khan were organisers of this Bahini.
Mukti Bahini consisted of the regular and the irregular forces. The regulars were later called 'Niomita Bahini' (regular force) and the irregulars were called 'Gono Bahini' (people's Force). The regulars included East Bengal Regiment and EPR troops. The irregular forces, which after initial training joined different sectors, consisted of the students, peasants, workers and political activists.
Irregular forces were inducted inside Bangladesh territory to adopt guerilla warfare against the enemy. The regular forces were engaged in fighting in conventional way. The first conventional brigade named as 'Z' Force was created in July. Major Ziaur Rahman was appointed commander of this brigade and the brigade was named as 'Z' Force after the first letter of his name. This brigade consisted of 1, 3 and 8 East Bengal. Second regular brigade 'S' Force was created in October and consisted of 2 and 11 East Bengal. 'S' Force was named after the initial letter of the name of its commander Shafiullah. Similarly the 'K' Force created with 4, 9 and 10 East Bengal which was commanded by Khaled Mosharraf.
Bangladesh Air Force, which was organised by Air Commodore A K Khondaker, was created in Dimapur of Nagaland on 28 September. Squadron Leader Sultan Mahmud, Flight Lieutenant Badrul Alam, Captain Khaleq, Sattar, Shahabuddin, Mukit, Akram and Sharfuddin and 67 airmen initially joined the Bangladesh Air Force, which had only few Dakota, Auter type air plane and Aluvet helicopters.