Battle of the Thousand Islands The Battle of the Thousand Islands during the French and Indian war ( also known as the Siege of Montreal ) was fought 16 – 24 August 1760 , in the upper St . Lawrence River , amongst the Thousand Islands , along the present day Canada – United States border , by British and French forces during the closing phases of the Seven Years ' War , as it is called in Canada and Europe , or the French and Indian War as it is referred to in the United States . The engagement took place at Fort Lévis ( about one mile ( 1 . 6 km ) downstream from the modern Ogdensburg – Prescott International Bridge ) , Pointe au Baril ( present - day Maitland , Ontario ) , and the surrounding waters and islands . The small French garrison at Fort Lévis held the much larger British army at bay for over a week , managing to sink two British warships and to cripple a third . Their resistance delayed the British advance to Montreal from the west . Background and forces . By August 1760 , the French were building Fort Lévis at " Île Royale " ( present - day Chimney Island New York ) in the St . Lawrence River . Captain Pierre Pouchot was assigned its defense . Pouchot had been taken prisoner after the siege of Fort Niagara , but he was later released in a prisoner exchange . Chevalier de Lévis ' original design for the fort called for stone walls , 200 guns and some 2 , 500 troops . What Pouchot had was a small fort with wooden stockades , five cannon and 200 soldiers . Also under Pouchot ' s command were the corvette s " l ' Outaouaise " and " l ' Iroquoise " , crewed by 200 sailors and voyageurs . " l ' Iroquoise " , under command of Commodore René Hypolite Pépin dit La Force , was armed with ten 12 - pound cannon and swivel gun s . " l ' Outaouaise " , commanded by Captain Pierre Boucher de LaBroquerie carried ten 12 - pounders , one 18 - pound gun and swivel guns . After the fall of Quebec in the 1759 Battle of the Plains of Abraham , British Commander - in - Chief General Jeffrey Amherst prepared to launch a three - pronged attack to take Montréal . Columns were to advance along the $ 3 from Quebec to the northeast , up the Richelieu River from Lake Champlain to the south , and from Oswego on Lake Ontario to the west . The latter force , which Amherst led personally , numbered some 10 , 000 men and 100 siege guns . Soon after his arrival to Île Royal , Pouchot ordered abandonment of the nearby mission Fort de La Présentation and the shipyard and stockades at " Pointe au Baril " to consolidate his resources at the more defendable Fort Lévis . La Force had run his corvette " l ' Iroquoise " aground at Pointe au Baril on 1 August . Although " l ' Iroquoise " was raised , it was deemed too damaged to be put into action . It was beached again under the guns at Fort Lévis . Amherst ' s force set out from Oswego on 10 August . Captain Joshua Loring , who commanded the British snow s " Onondaga " and " Mohawk " , had been sent ahead of Amherst ' s force as an advance guard . The " Onondaga " , had been launched at Fort Niagara as the " Apollo " in 1759 . Commanded by Loring , it carried four 9 - pound guns , fourteen 6 - pounders and a crew of 100 seamen and 25 soldiers . The " Mohawk " , commanded by Lieutenant David Phipps , carried sixteen 6 - pounders and a crew of 90 seamen and 30 soldiers . Battle . On 7 August , French lookouts sighted the " Onondaga " and the " Mohawk " from their outpost at Ile aux Chevreuils , upstream from Fort Lévis . The French withdrew in a row galley , pursued by the " Onondaga " and the " Mohawk " . The two British ships got lost in the maze of islands , and did not find their way back to the main channel for several days . Amherst ' s force arrived at Pointe au Baril on 16 August . Fearing the remaining French ship might attack his transports , Amherst ordered Colonel George Williamson to capture " l ' Outaouaise " the following day . At dawn of 17 August , Williamson set out in a gig , accompanied by five row galley s ( one armed with a howitzer , the others each armed with a single 12 - pounder ) . The galleys took shelter fore and aft of " l ' Outaouaise " , where they could not be hit by the ship ' s broadsides . The British galleys fired grapeshot and round shot at the French ship , crippling " l ' Outaouaise " , which drifted helplessly towards the British battery set up at Pointe au Baril . After three hours of fighting , " l ' Outaouaise " had managed to fire around 72 shots , damaging two of the British galleys . LaBroquerie was forced to surrender " l ' Outaouaise " to Williamson . LaBroquerie was wounded in the fighting . Fifteen members of his crew were killed or wounded . The captured " l ' Outaouaise " was repaired and renamed " Williamson " , to be put back into service by Captain Patrick Sinclair against her former owners . On 19 August , Amherst commenced the attack on Fort Lévis . La Force and his crew had been ordered back from the beached " l ' Iroquoise " to the fort to assist with its defense . The " Williamson " was hit 48 times by the five French guns when it joined in with the British batteries firing on Fort Lévis from surrounding islands . The " Mohawk " and " Onondaga " finally arrived at the scene in the evening and Amherst called a ceasefire for the night . The attack resumed at dawn on 20 August with the " Williamson " , " Mohawk " and the " Onondaga " all firing on the fort with a combined 50 guns . As the attack progressed , the French guns hit and sank the " Williamson " and the " Onondaga " . The " Mohawk " ran aground under the French cannon , where it sat helpless as it was pounded until out of action . The British batteries on the surrounding islands continued to fire , switching to " hot shot " , used to start fires within the fort . The siege continued until 24 August when Pouchot ran out of ammunition for his guns and asked for terms . Aftermath . The fighting cost the British some 26 killed and 47 wounded ( likely excluding militia ) to the French losses of around 275 of the original 300 defenders killed or wounded . Pouchot was amongst the wounded . The British could hardly believe that such a small garrison had offered such spirited resistance . After the battle , Amherst ' s force remained at Fort Lévis for another four days before continuing toward Montréal . The British advance cost Amherst at least 84 more men drowned in the rapids of the St . Lawrence ( although Pouchot puts this number at 336 ) . He went on to meet the forces from Quebec and Lake Champlain and completely surrounded Montréal . On 6 September , Montréal was surrendered by New France ' s governor , the Marquis de Vaudreuil . The British renamed Fort Lévis to Fort William Augustus . They raised the three ships sunk during the battle ( the " Williamson " , the " Onondaga " and the " Mohawk " ) and put them back into service to patrol the waters between the fort and Fort Niagara .