Beira Patrol The Beira Patrol was a blockade of oil shipments to Rhodesia ( now Zimbabwe ) through Beira , Mozambique , resulting from United Nations trade sanctions on Rhodesia . Background . Rhodesia ' s mostly white minority government unilaterally declared the former colony ' s independence on 11 November 1965 , after rejecting British preconditions for independence that involved racial equality and rule by the black majority . Ian Smith , the country ' s elected prime minister , continued in that role . The United Nations Security Council reacted by passing Resolution 217 , calling for sanctions on Rhodesia . The resolution was later used by the British as legal justification for the blockade . Britain imposed its own national sanctions , including an oil embargo , but ruled out invading Rhodesia . The British were initially opposed to military action , instead relying on UN sanctions to pressure the Rhodesians . A majority of UN member states wanted expanded sanctions and military measures . The British initially attempted to block such initiatives . In October 1965 , the Joint Intelligence Committee estimated that even a full trade embargo would fail to cripple Rhodesia ' s economy , but suggested that prolonged and severe economic pressure could induce the white electorate to overthrow the government . In early 1966 , Prime Minister Harold Wilson made statements that sanctions were working , predicting that the Rhodesian government would soon fall . At the same time , the Foreign Office was looking into the possibility of a maritime blockade . During the first week of February 1966 , it became clear that Rhodesia continued to import oil by land from South Africa , and Prime Minister Wilson was warned that black African states could push for more urgent sanctions and raise the matter at the UN . On 24 February , the Chiefs of Staff Committee warned that tankers with oil for Rhodesia could arrive in the port of Beira , the terminus of a pipeline going to Rhodesia , unnoticed , and began preparing a maritime surveillance plan for submission to the Prime Minister . Later in February , the British government and world press began focusing on tankers carrying oil for Rhodesia when on 25 February , the Rhodesian Commerce and Industry Minister announced that a tanker with oil for Rhodesia would soon arrive . Blockade . Following the reports of Rhodesia defying the oil embargo by sea , the British felt pressure to take action and thus prove their commitment to sanctions . On 1 March , the Royal Navy established the Beira Patrol and stationed the frigate HMS " Lowestoft " off Beira , directing it to prepare for intercept operations starting on 4 March . On 6 March , early warning aircraft from the carrier HMS " Ark Royal " began search operations in the Mozambique Channel . The frigate HMS " Rhyl " and a logistical support ship were soon added . The patrol lasted until 1975 . At any time , two British frigates or destroyers , with the support of land and carrier - based surveillance aircraft and auxiliary vessels , were committed to the patrol . Various British warships cruised the Mozambique Channel from Beira and checking on oil tankers heading for the port . Initially , Royal Navy ships were to shadow and question Beira - bound tankers , and were only allowed to forcibly divert a tanker away after Britain obtained permission from its flag state . However , in the event that permission was granted , British warships were only allowed to demand it change course in the name of its flag state , and fire a shot across the bow if it did not work . The use of force was not authorised , and if the tanker absolutely refused to comply , the shadowing warship could take no more action and only follow it to within Mozambique ' s six - mile territorial limit . This meant that the tanker would be allowed to proceed unhindrered to port . After an incident where the Greek tanker " Joanna V " freely sailed into Beira after Greece refused to grant permission , the British lobbied for UN authority to use force . The UN Security Council subsequently passed Resolution 221 . However , resolution confined the blockade to Beira and authorised only the Royal Navy to use force . As a result , the Royal Navy alone had to enforce the blockade without assistance , and tankers with oil for Rhodesia could freely dock at other Mozambican ports . The resolution also empowered the British to seize the " Joanna V " upon its departure from Beira if it had discharged its oil cargo there . The rules of engagement were subsequently liberalised , but use of force was limited " to the very minimum " , and Defence Ministry approval was required for the diversion of vessels . British warships also had to remain outside of Mozambique ' s territorial waters . After an embarrassing incident involving the French tanker " Artois " , the rules of engagement were further modified , allowing the use of disabling fire . Britain never managed to obtain UN authority allowing other navies to participate . As well as lacking UN permission , the British judged it outside their capabilities to blockade other Mozambican ports . South Africa was also capable of transporting oil to Beira by keeping having tankers cruise through South African and then Mozambican territorial waters , providing legal immunity from interception . As a result , Rhodesia continued to receive oil shipments . Rhodesia was also able to withstand the blockade by strictly rationing oil . In September 1966 , it was estimated that Rhodesia received 220 , 000 gallons of oil daily , when it needed only 200 , 000 a day under its rationing policy . The patrol was gradually reduced in several stages . In March 1971 , new Prime Minister Edward Heath allowed the Royal Navy to commit one warship at a time , rather than two . Three months later , the patrol lost its air component when the Malagasy Republic asked the Royal Air Force to eliminate its detachment at Majunga . After an overall drop in the number of frigates in the fleet , the Royal Navy was allowed to make the patrol intermittent . The patrol was finally eliminated on 25 June 1975 , when Mozambique gained independence from Portugal and assured Britain that it would not allow transship oil to Rhodesia . The operation had cost an estimated 100 million pounds , and 76 Royal Navy ships took part in the operation . A total of 47 oil tankers were intercepted , of which 42 were allowed to proceed .