The Congress of United States declared war on Great Britain on 18 June 1812. Appreciating the significance of Fort St. Joseph, Major-General Sir Isaac Brock, military commander of Upper Canada, sent a message to Captain Charles Roberts, commander of Fort St. Joseph, ordering to prepare for immediate attack on Michilimackinac. On 16 July 1812, Captain Roberts and an army of British soldiers, French Canadian voyageurs (most of them from nearby Sault Ste. Marie), and about four hundred Ottawa, Ojibwa, Menominee, and Winnebago warriors set off on an flotilla towards Fort Michilimackinac. The mission was accomplished without major incident and the task force landed at British Landing on Mackinac Island on the morning of 17 July 1812. Lieutenant Porter Hanks, commander of Fort Michilimackinac, was unprepared for an attack and Fort Michilimackinac was severely under-manned. Before Lieutenant Hanks' men could act, Captain Roberts's army had already taken position and Hanks had no choice but to surrender.