Battle of Fort Oswego ( 1756 ) The Battle of Fort Oswego was one in a series of early French victories in the North American theatre of the Seven Years ' War won in spite of New France ' s military vulnerability . During the week of August 10 , 1756 , a force of regulars and Canadian militia under General Montcalm captured and occupied the British fortifications at Fort Oswego , located at the site of present - day Oswego , New York . In addition to 1 , 700 prisoners , Montcalm ' s force seized the fort ' s 121 cannon . The fall of Fort Oswego effectively interrupted the British presence on Lake Ontario and removed it as a threat to the nearby French - controlled Fort Frontenac . The battle was notable for demonstrating that traditional European siege tactics were viable in North America when applied properly in the right circumstances and terrain . Background . Following the beginning of open conflict between French and British colonists in 1754 with the Battle of Jumonville Glen , the governments of Britain and France both sent regular army troops to North America to further contest the disputed territories of the Ohio Country and other border areas , including the frontier between the French province of Canada and the British province of New York , an area in present - day Upstate New York that was then largely controlled by the Iroquois nations . Part of the British plans for 1755 included an expedition to take Fort Niagara at the western end of Lake Ontario . The planned route for this expedition followed the Oswego River to the lake , with a major base of operations at the mouth of the river ( where the present - day city of Oswego , New York is located ) . Under the direction of William Shirley , the governor of the Province of Massachusetts Bay , the original Fort Oswego was reinforced , and two additional forts , Fort George and Fort Ontario , were built in 1755 . The planned expedition to Fort Niagara never took place due to logistical difficulties , and the fortifications around Oswego were manned during the winter of 1755 – 56 . The French in 1755 had the only large naval vessels on Lake Ontario , and moved freely about the lake , between Fort Niagara in the west and Fort Frontenac at the head of the Saint Lawrence River . In March 1756 they launched a winter attack on Fort Bull on Wood Creek . Fort Bull was a key depot on the supply line for the Oswego forts , which was the waterway leading up the Mohawk River and crossing over to the Oswego River watershed . In the successful attack , they destroyed many provisions intended for the Oswego garrison , and effectively ruined Shirley ' s plan to attempt the expedition against Fort Niagara in 1756 . Following orders of the Governor of New France , Pierre François de Rigaud , Marquis de Vaudreuil - Cavagnal , in May 1756 French and Indian raiding parties under the command of Louis Coulon de Villiers began harassing the Oswego garrison from a camp on Henderson Bay ( south of present - day Sackett ' s Harbor , New York ) . General Louis - Joseph de Montcalm arrived in Montreal in May 1756 to lead the French army troops . He and Governor Vaudreuil took an immediate dislike to one another , and disagreed over issues of command . Concerned over the massing of British troops at the southern end of Lake George , Montcalm first went to Fort Carillon on Lake Champlain to see to its defenses . Vaudreuil meanwhile began massing troops at Fort Frontenac for a potential assault on Oswego . Following favorable reports from the raiding parties , Montcalm and Vaudreuil decided to make the attempt . Governor Shirley received word in March 1756 that he was to be replaced by John Campbell , 4th Earl of Loudoun . Loudoun ' s second in command , General James Abercrombie , only arrived in Albany in late June , and Shirley spent the intervening time shoring up the supply line to Oswego in anticipation of leading an expedition against the French forts on Lake Ontario . In June William Johnson traveled to the Iroquois headquarters at Onondaga , and successfully negotiated support for the British side with the Iroquois , Shawnee , and Delaware , forces that Shirley also hoped to use for his expedition . Shirley also hired 2 , 000 armed " battoemen " , men experienced in sailing and shipbuilding . Under the command of John Bradstreet , these men successfully resupplied the forts at Oswego in July , although they were attacked by a French raiding party on their way back , suffering 60 to 70 casualties . When Loudoun arrived in Albany in late July , he immediately cancelled Shirley ' s plans for an Oswego - based expedition . Defenses at Oswego . The complex of defenses at Oswego consisted of three separate fortresses . On the east side of the Oswego River lay Fort Ontario , a log fortification which was constructed in 1755 , was sited on a rise overlooking the mouth of the river . It was garrisoned by 370 men from Pepperrell ' s Regiment , and was in fairly good repair . Fort Oswego was on the west side of the river , and had a central structure of stone and clay surrounded by earthworks to the south and west , but fully exposed to Fort Ontario , across the river . A recently constructed Fort George ( called " Fort Rascal " by one of Shirley ' s Regiment , which occupied Fort Oswego ) consisted of an incomplete wooden palisade fort that lacked even loopholes through which defenders could fire , and was occupied by 150 New Jersey militiamen . The latter two forts did not have very much shelter for the occupying garrison , and there were only a few cannon for the entire complex of defenses . Significant elements of the two Massachusetts regiments , which were under the overall command of Colonel James Mercer of Pepperrell ' s Regiment , had overwintered there , and suffered significantly due to the shortage of supplies , especially food . Many men died during the winter from diseases such as scurvy , and there had been serious discussion of abandoning the position for want of supplies . While the garrison nominally approached 2 , 000 men in size , less than 1 , 200 men were fit for duty . French approach . Montcalm left Carillon on July 16 under the command of the Chevalier de Levis , reaching Montreal three days later . Two days later he left for Fort Frontenac , where French troops were gathering along with a large company of Indians . French forces included the battalions of La Sarre , Guyenne , and Béarn , troupes de la marine , and colonial militia , while Indians , numbering about 250 , came from all over the territories of New France . The total size of the force was reckoned to be 3 , 000 men . The governor ' s brother , François - Pierre de Rigaud , led an advance force of 700 to meet with Villiers ' force at Sackett Harbor before the main force set out on August 4 . Crossing at night to what is now called Wolfe Island , the vanguard of the main body spent the day there before crossing at night to Sackett ' s Harbor . By August 8 the entire force was assembled there , and set out the next day for Oswego . On August 9 , troops under Rigaud and Villiers marched overland toward Oswego , while Montcalm and the remaining force moved close to the shore in bateau x , landing about east of Fort Ontario early on August 10 . Their stealth in movement was successful , and the British did not discover them until a small patrol boat spotted them the next morning . Larger boats sent by the British were driven away by the French field artillery . Battle . Montcalm ' s engineer went to survey the British defenses , accompanied by other officers and a party of Indians . One of the Indians , eager for a scalp , mistook the engineer for a British soldier at one point and shot him dead . Montcalm asked Pierre Pouchot to continue with the work of determining how to besiege the British positions . On the night of August 11 – 12 the French opened siege trenches and began working toward Fort Ontario . The fort ' s defenders exchanged cannon and gunfire with the French colonists and Indians until late in the day on August 13 , at which point , apparently under orders from Mercer , they abandoned the fort even before the siege trenches had reached their goal . Immediately capitalizing on this , Montcalm occupied the fort and began the construction of batteries on the western edge of the height , where they could reach Fort Oswego ' s exposed east side . Moving with all speed , the French had nine working cannon established by the morning of August 14 . When these opened fire on the exposed stonework of Fort Oswego , the walls crumbled under the onslaught . The garrison , whose cannon were all pointed away from the river ( not expecting enemy fire to come from that direction ) , eventually turned their guns around , and the French fire was returned to some effect . However , Montcalm had ordered Rigaud to lead some men across the river upstream from the fortifications , and these men , who made an unopposed crossing under somewhat difficult conditions , appeared on the edge of the clearing outside Fort Oswego about the same time that Colonel Mercer was struck and killed by a French shell . After a short council Colonel John Littlehales , who took over command from Mercer , raised the white flag . Aftermath . The British surrendered about 1 , 700 people , including laborers , shipbuilders , women and children . When the fort was opened to the Canadian militia and Indians , they rushed in and began plundering the fort , opening the barrels of rum and getting drunk on the contents . Amid the confusion some of the British tried to escape , and were tomahawked and killed by drunken French or Indians . Colonel Littlehales was seized by a group of Abenakis and badly beaten because " he was a coward and had behaved ill . " General Montcalm , shocked by the behavior , was eventually able to prevent further killings , although he claimed it would " cost the King eight or ten thousand livres in presents . " He then ordered the destruction of all the supplies the French did not take , as well as the boats under construction , after which the entire company , including the prisoners , traveled to Montreal . On August 12 , Loudoun finally dispatched reinforcements from the 44th Regiment of Foot and Bradstreet ' s battoemen toward Oswego . When these troops reached the Oneida Carry they learned that Oswego had fallen ; after destroying the fortifications there , they retreated to German Flatts , where Loudoun ordered them to stay to prevent further French advances . Loudoun spent significant effort over the following months to pin the blame for the loss on William Shirley . He was cleared of all formal charges in an inquiry , but numerous irregularities were highlighted . Shirley ' s political connections in London enabled him to acquire other desirable posts later in his career . Oswego was effectively abandoned until 1758 , when the British reoccupied the area , and Bradstreet led an expedition that captured and destroyed Fort Frontenac . It was used again in 1759 as a departure point for a successful expedition against Fort Niagara , and in 1760 by Jeffrey Amherst ' s army as it moved toward Montreal .