On May 4, about 900 British sailors supplemented by 400 marines started working to get 4 ships, 2 brigs and 2 schooners ready while 550 soldiers crowded on the war ships. These ships were going to tow bateaux and gunboats. At 4:00 A.M., they weight anchor and sailed out of Kingston Harbour and onto Lake Ontario.
At first light on May 5, the lookouts at Fort Oswego sighted the British and passed the word quickly to Commandant Melanthon Woolsey and Lt. Col. George Mitchell, 3rd U.S. Artillery Regiment, who hurried to see for themselves.
The situation was a difficult one since they were ordered to protect the naval stores that had been accumlating at the fort earmaked for Sacket's Habor, but their defensive force was small and their tactical position was weak.
Mitchell had 290 men under his command, they had been part of Gen. Brown's army at Batavia, New York until they were ordered to defend Fort Oswego.
They had arrived on April 30, and moved into the fort atop the hill on the eastern shore of the bay. The British had built Fort Oswego almost a century before, and the site had been formidable. But over the years, it's defensive fortifacations had disappeared. There still were some low buildings and barracks standing in the compound, and the Americans had 5 small-caliber guns on hand, but all lacking proper carriages, and 3 of them without trunnions.
Mitchell's gunners built the carriages and platforms for the ordnance, installing 3 to face the lake and the other 2 guns toward the long glacis that stretched to a landing place east of the fort. They also built pickets to replace the old ones that had once skirted the fort.
As the British came into view, Mitchell decided to keep his men out of sight until he knew what the British intentions were. He did have one of his companies standing ready to man the guns, the others would be used as infantry.
Woolsey and Mitchell decided to stand and fight the best they could, but agreed that if they faced being captured they would retrest to Fredericksburgh.
The British had been making their slow advance all morning. They stopped just beyond the range of the American guns and started to bring around the landing boats. After one attempt to load the landing craft was aborted due to a risk of a bad storm, the British were able to try landing once more at 6:00 A.M. The guns onboard the British ships opened up chasing away the American militia. Mitchell's 2 batteries opened fire back at the British ships while the infantry was safely behind the thick walls of the fort.
Capt. Popham brought his ship, the HMS Niagara, in close to the fort and anchoed. The Niagara now pounded the Americans with their broadside of 9 guns. Using a shot oven to heat their shot until it was nearly redhot, the American gunners returned fire and set the British ship on fire 3 times.
The British landed about 2:00 P.M., but were not quite on shore when their officers, setting an example for their men jumped off the boats and sank nearly out of sight.
Making it to shore, the Royal Marines, De Watteville Regiment and the Glengarry Light Infantry, checked their ammunition only to find that nearly all of it was ruined by their advance through deep water, so they all fixed bayonets. The American forces were firing well aimed vollys from the woods and the glacis, so Lt. Col. Fischer ordered the Glengarries to clear the woods of the Americans, which they did quicky.
On the other side of the fort, the British made a second landing and getting ready to charge up the hill and dislodge the American from the main battery. This charge was led by Capt. Mulcaster.
Back at the first landing area, Fischer gave the order for the whole force to advance quickly and charge up the hill. The British could not fire their muskets as all their ammunition had been ruined while they landed. While they advanced, the Americans continued to fire devastating vollys on them. The British continued forward with bayonets fixed. The American vollys were knocking down dozens of British soldiers.
One captain and 6 marines were killed and 33 others suffered wounds. The De Wattevilles Regiment lost 8 killed and 20 wounded. The Glengarry Light Infantry were a bit more fortunate with only 9 men wounded.
Back on the opposite side of the fort, Capt. Mulcaster's sailors landed and quickly made their way up toward their objective. Armed with pikes and cutlasses, they sought to over power Mitchell's gunners who were defending themselves with muskets. Mulcaster was leading the charge when he watched an American aim and fired at him. He was not able to move out of the way in time to avoid the musket ball, which hit his leg. The British rallied and continued up into the American battery all the while under heavy fire.
Back on the eastern side of the fort, the British were having a hard time with the American defenders who were inspired by the faltering British line. A wave of British Marines managed to make their way into the northwest corner and ran down into the fort, while the sailors beat their way into the battery. The Mitchll knew at this point his forces were being over powered and ordered a retreat.
It was about 30 minutes since the British landed and one of the British seamen was making his way to the flag pole in the center of the fort. He jumped up onto the pole and started to scale it. The Americans, angered by this sight, started pouring volleys of fire at the man, for they knew what he was about to do. More and more Americans began firing at him, hitting him a number of times. Never the less, he continued up the pole and upon reaching the top, he tore down the American flag and let it fall to the ground as the British forces cheered loudly.
The Americans made their retreat with whatever wounded could walk. They scuttled the last of the boats so they would not fall into British hands and headed for Fredericksburgh.
Fort Oswego and the surrounding village fell to the British. They secured the area and sent reserves to shore to help with the many tasks, which included tending to the wounded, dead and prisoners. They also found an American captain and 25 or so dead men, and the British buried them. Twenty-five American prisoners were transported to the British warships.
The afternoon and evening of May 6, the British transported all the goods they captured from the Americans at Fort Oswego to their warships.
The items siezed were four 24-pdr and three 32-pdr long guns, more than 300 shot of all description and calibers. Some of the items were taken from some of the boats the Americans had scuttled as they retreated. They Also captured the schooners USS Growler and the USS Penelope.