Battle of Rio de Janeiro The Battle of Rio de Janeiro was a raid in September 1711 on the port of Rio de Janeiro in the War of Spanish Succession by a French squadron under René Duguay - Trouin . The Portuguese defenders , including the city ' s governor and an admiral of the fleet anchored there , were unable to put up effective resistance in spite of numerical advantages . Four Portuguese ships of the line were lost , and the city had to pay a ransom to avoid destruction of its defences . Background . There were multiple reasons for the French to plan an attack on Rio de Janeiro . Firstly , the commander Duguay - Trouin had a personal reason : he was almost bankrupt . The second reason was political . The war had not gone well for France . After the defeat in the Battle of Malplaquet , the enemy was on French soil and French morale was low . A military success was urgently needed . The third reason was a question of honour . The previous year another buccaneer , Jean - François Duclerc had attempted an attack on Rio , but this expedition had ended in disaster ; Duclerc and 600 of his soldiers were captured and held in unacceptable conditions . The Portuguese refused to exchange these prisoners as was stipulated in a Franco - Portuguese treaty from 1707 ; furthermore , Duclerc was killed in prison under mysterious circumstances in May 1711 . The French wanted to liberate these prisoners , and possibly conquer some Brazilian territory . Preparations . In December 1710 King Louis XIV approved Duguay - Trouin ' s plan and provided him with a fleet of 17 ships , carrying in total 738 cannons and 6 , 139 men . The French treasury couldn ' t finance the armament of the squadron and therefore Duguay - Trouin had to search private financiers in Saint Malo and on the Royal Court ; he received significant support from the Count of Toulouse . Finally the ships could be prepared and to fool the British Navy , allied to the Portuguese , the ships were prepared in different harbours , left at different times , and reassembled at sea off La Rochelle on June 9 , 1711 . British intelligence , however , were aware of Duguay - Trouin ' s goal , and had dispatched a packet to warn the Portuguese , both in Portugal and at Rio . They also dispatched a fleet under John Leake to blockade Duguay - Trouin before he sailed from Brest ; they arrived two days too late . The battle . In spite of the British warning , the French appearance in Rio ' s harbour on 12 September was a surprise . The British news , when it arrived in August , had led Governor Francisco de Moraes de Castro to call out his militia and increase preparedness , and rumours of sails off Cabo Frio in early September had again raised the alert . However , on 11 September the governor ordered the militia to stand down , just as Duguay - Trouin was preparing his approach to the harbour . The commander of " Le Lys " , Courserac , led the squadron directly in the Bay of Rio , between the forts lining the harbour entry , and straight at seven Portuguese warships that were anchored there . The Portuguese fleet commander , admiral Gaspar da Costa , could do nothing but cut the cables in hopes of getting his ships moving . Three of battleships grounded and were destroyed by the Portuguese to prevent their capture ; the fourth was taken by the French and burned . Fire from the forts , undermanned after the order to stand down , did some damage to the French fleet , inflicting 300 casualties before the ships passed out of range . After 3 days of bombardments , the French landed 3 , 700 men to attack the city . The governor of Rio , Castro - Morais , had fortified the city after French attacks in previous years , but very feebly commanded the defense , which buckled under the French bombardment . After a council on 21 September in which Moraes ordered the city ' s defenders to hold the line , militia began deserting that night , after which there began a general flight from the city that included the governor . Under the disorganised circumstances , the French prisoners from Duclerc ' s expedition broke out of prison . Aftermath . Duguay - Trouin , who had been preparing to storm the city , was alerted to the flight of the defenders by the arrival of one of Duclerc ' s men . Over the next few days , the French gained control of all of the bay ' s strong points , but the city ' s gold supply eluded him . Warned that reinforcements from São Paulo under command of António de Albuquerque were on their way , he threatened Moraes with the destruction of the city ' s defences if a ransom was not paid , which Moraes agreed to do . When the French left the city , it was with loot of estimated at 4 million pounds , including a shipment of African slaves , which Duguay - Trouin later sold in Cayenne . The fleet arrived back unmolested in Brest in February 1712 . The expedition was a military success for the French , and a financial success for its investors . The French Navy had proven it was still capable to strike at large distances . This action would trouble Franco - Portuguese relations for many years to come . External links . city