Bangladesh–Soviet Union relations were the bilateral relations between the People's Republic of Bangladesh and the Soviet Union, lasting from the recognition of Bangladeshi independence in January 1972 until the dissolution of the Soviet Union in December 1991.

The Soviet Union had been a supporter of Pakistan's territorial integrity for most of 1971, treating the crisis in East Pakistan as an internal Pakistani matter while pressing Yahya Khan to seek a political settlement. As the war went on, Moscow shifted decisively towards India and the Bengali nationalist cause, signing the Indo-Soviet treaty in August 1971 and, in December, vetoing Security Council ceasefire resolutions that would have halted the fighting without addressing the political crisis in the east. Soviet warships entered the Bay of Bengal in response to the American Task Force 74, and Pakistani forces surrendered at Dhaka on 16 December 1971.

Relations were at their closest under Sheikh Mujibur Rahman between 1972 and 1975. Moscow recognised Bangladesh on 24 January 1972, diplomatic relations were established the following day, and Mujib visited Moscow in March 1972, signing agreements on economic, technical, cultural and scientific cooperation. The best-remembered Soviet contribution was a naval salvage operation that cleared mines and sunken vessels from the Port of Chittagong between 1972 and 1974 at no cost to Bangladesh, in the course of which one Soviet sailor was killed. Soviet economic aid, however, was modest beside that of India, the United States and Western institutions, and Bangladesh's commitment to non-alignment limited how far Dhaka would lean towards Moscow.

The relationship deteriorated sharply after the assassination of Mujib in August 1975. The military governments of Ziaur Rahman and Hussain Muhammad Ershad moved towards the United States, China and the Arab states; Bangladesh condemned the Soviet intervention in Afghanistan and joined the boycott of the 1980 Moscow Olympics. Ties reached their lowest point in late 1983 and early 1984, when Ershad's government ordered the Soviet embassy to reduce its staff, closed the Soviet consulate in Chittagong and expelled a number of Soviet diplomats. Relations recovered gradually in the second half of the 1980s. Bangladesh recognised the Russian Federation as the successor state to the Soviet Union on 29 December 1991.

Background Soviet policy in South Asia before 1971 aimed at regional stability and at limiting the influence of both the Western powers and China. After the British withdrawal from East of Suez in the late 1960s, Moscow judged that the United States and its allies were looking to fill the vacuum, and Leonid Brezhnev's proposal for a system of collective security in Asia, announced in 1969, treated both India and Pakistan as potential partners. The Soviet Union had brokered the Tashkent Declaration between India and Pakistan after the 1965 war and saw itself as the guarantor of that settlement.

Moscow's view of the Awami League had historically been unfavourable, since its former leader Huseyn Shaheed Suhrawardy had taken Pakistan into Western anti-Soviet alliances. By 1970, with Pakistan's radical left parties leaning towards Beijing, Soviet analysts were reassessing "bourgeois" parties as potentially progressive, and after the 1970 election Sheikh Mujibur Rahman was being described in Moscow as a secular, socialist and non-aligned figure comparable to Jawaharlal Nehru. The pro-Soviet National Awami Party (Muzaffar) and the pro-Moscow communists in East Pakistan provided a further channel of contact.

Liberation War of 1971 The Pakistan Army's crackdown of 25 March 1971 disrupted Soviet calculations. On 2 April, the Soviet head of state Nikolai Podgorny wrote to Yahya Khan calling for urgent measures to stop the bloodshed and repression in East Pakistan and for a turn to peaceful political settlement; the letter's reference to the interests of "the entire people of Pakistan" nonetheless implied continued support for Pakistani unity. Yahya replied sharply, asking Moscow to restrain Indian interference, and Zulfikar Ali Bhutto called the letter blatant interference in Pakistan's internal affairs. Into May, the Soviet position remained that the crisis was an internal Pakistani matter best resolved without breaking up the state, lest China and the Western powers benefit from its disintegration.

Two developments changed this. The refugee exodus drew India into the crisis, and a joint communiqué issued after the Indian foreign minister Swaran Singh visited Moscow on 8 June 1971 acknowledged the need for conditions allowing refugees to return, tacitly conceding that the matter was no longer purely internal. At the same time the pro-Moscow Bengali left pressed the Kremlin to view the struggle as a case of national self-determination and to note that China was aligning with Pakistan. With Henry Kissinger's secret visit to Beijing in July raising the prospect of a Sino-American understanding, Moscow moved to formalise its relationship with New Delhi, and the Treaty of Peace, Friendship and Cooperation was signed on 9 August 1971. Efforts to mediate continued into the autumn and failed, including a meeting on 24 October between the Soviet deputy foreign minister Nikolay Firyubin and the provisional prime minister Tajuddin Ahmad, who refused to moderate the demand for independence.

When full hostilities began in December, Brezhnev framed the conflict as the product of the suppression of the expressed will of the East Pakistani population and insisted that a ceasefire and a political settlement based on the 1970 election results were inseparable. That formula governed Soviet conduct at the United Nations Security Council, where the ambassador Yakov Malik opposed American-backed resolutions calling for a ceasefire first, arguing that they ignored the root cause of the fighting and wrongly equated India and Pakistan. The Soviet Union vetoed such resolutions three times during the December fighting, the first two on 4 and 5 December. By preventing a ceasefire from preceding a settlement, Moscow allowed the fighting to run to its conclusion in the surrender of Pakistani forces on 16 December.

Soviet support was also demonstrated closer to the theatre. The first deputy foreign minister Vasily Kuznetsov arrived in New Delhi on 11 December, and on 13 December the Soviet ambassador Nikolai Pegov assured Indira Gandhi that Moscow would open diversionary action in Xinjiang if China intervened. After the American Task Force 74, centred on the carrier , passed through the Strait of Malacca on 14 December, Soviet warships followed three days later, forestalling intervention on Pakistan's behalf.

Recognition and the Mujib years Moscow was in no hurry to recognise the new state, doing so on 24 January 1972, more than a month after independence; diplomatic relations were established the next day by an exchange of notes. Iftekhar Ahmed Chowdhury attributes the delay to Soviet circumspection and notes that Dhaka did not resent it, since Mujib's priority was to secure recognition from the Western world and China rather than from a bloc whose support was assured.

Mujib visited Moscow from 1 to 5 March 1972, his second foreign destination after India. The visit produced intergovernmental agreements on economic and technical cooperation, trade and Soviet trade representation, air services, cultural and scientific cooperation, and assistance in restoring navigation in Bangladeshi seaports. An agreement signed on 2 March provided Bangladesh with three freight ships, four Mil Mi-8 helicopters with crews for a year, fifty locomotives and a cold storage plant.

Chittagong salvage operation The Port of Chittagong, Bangladesh's principal harbour, had been mined and littered with sunken vessels during the war, and commercial salvage firms quoted prices the new state could not meet. Mujib raised the problem with Brezhnev and the defence minister Andrei Grechko during his Moscow visit, and an agreement on free assistance in restoring navigation was signed in Dhaka on 21 March 1972.

The Soviet Navy's Special Expedition 12 was drawn from the Pacific Fleet at Vladivostok. An advance party of about a hundred men under Rear Admiral Sergey Pavlovich Zuenko reached Chittagong on 2 April 1972, followed by the main flotilla of 22 vessels and some 700 sailors, for a total of about 800 personnel. Work continued for about 26 months, ending in June 1974, and cleared twelve berths and raised 26 sunken ships. A senior sailor of the floating workshop PM-156, Yuri Viktorovich Redkin, was killed on duty on 13 July 1973 and was buried with military honours at Chittagong; a memorial to him stands in the grounds of the Bangladesh Naval Academy.

Not all assessments at the time were admiring. A United States intelligence survey of early 1973 recorded that the salvage fleet had been at work for over eight months with another year's work expected, and cited a Swiss press report that Mujib was pressing for an early end to the operation and wanted a written Soviet undertaking to leave the port.

Aid, trade and the limits of cooperation Soviet economic assistance was real but limited. In the first four months of Bangladesh's existence it received economic aid worth US$142 million from India but only US$6 million from the Soviet Union, and by early 1973 American analysts put cumulative Soviet aid at about US$120 million out of roughly US$1 billion received from all sources. By March 1973, Bangladesh had received about US$136 million from the Soviet Union against US$318 million from the United States and US$262 million from India.

Soviet technical assistance concentrated on the energy sector, above all the thermal power stations at Ghorashal and Siddhirganj, commissioned in the mid-1970s. Trade was conducted largely by barter, with Bangladesh exporting jute, tea and leather in exchange for industrial goods and minerals. The Soviet Union supplied the aircraft with which the Bangladesh Air Force was initially equipped, together with training and spares. Large numbers of Bangladeshi students received scholarships to Soviet universities, and a Soviet cultural centre was established in Dhaka in March 1974.

Chowdhury identifies several constraints that kept the relationship from deepening. Bangladesh depended heavily on Western donors and on the World Bank and International Monetary Fund, which cut against any Soviet design to detach it from the West; Moscow's higher priority on India meant Dhaka's standing fluctuated with the state of Indo-Bangladeshi relations; and Soviet cultural influence on the Bangladeshi elite remained slight as the middle class built its links with the West. No Soviet cabinet minister ever visited Bangladesh. For Mujib, non-alignment mattered more than leaning towards either superpower.

Estrangement, 1975–1984 Relations cooled rapidly after the coup of August 1975 in which Mujib was killed. The governments of Ziaur Rahman and, from 1982, Hussain Muhammad Ershad de-emphasised socialist policies and cultivated the United States, the Arab states, Pakistan and China. Bangladesh criticised Soviet backing for the Vietnamese intervention in Cambodia and opposed the Soviet war in Afghanistan, hosting a conference of Islamic Conference foreign ministers that called for the withdrawal of foreign troops, and it joined the boycott of the 1980 Moscow Olympics. In 1980 four Soviet diplomats were expelled over allegations that the embassy had imported communications equipment for intelligence purposes.