Having been a serving soldier, he quickly appreciated the situation on Lake Ontario and devised a plan by which a force of 7,000 regular soldiers would be concentrated at Sackett's Harbor on April 1. Working together with Chauncey's squadron, this force would capture Kingston before the Saint Lawrence River thawed and substantial British reinforcements could arrive in Upper Canada. The capture of Kingston and the destruction of the Kingston Royal Naval Dockyard together with most of the vessels of the Provincial Marine, would make almost every British post west of Kingston vulnerable if not untenable. After Kingston was captured, the Americans would then capture the British positions at York and Fort George, at the mouth of the Niagara River. Armstrong conferred with Major General Henry Dearborn, commander of the American Army of the North, at Albany, New York during February. Both Dearborn and Chauncey agreed with Armstrong's plan at this point, but they subsequently had second thoughts. That month, Lieutenant General Sir George Prévost, the British Governor General of Canada, travelled up the frozen Saint Lawrence to visit Upper Canada. This visit was made necessary because Major General Roger Hale Sheaffe, who had succeeded Brock as Lieutenant Governor of Upper Canada, was ill and unable to perform his various duties. Prévost was accompanied only by a few small detachments of reinforcements, which participated in the Battle of Ogdensburg en route. Nevertheless, both Chauncey and Dearborn believed that Prévost's arrival indicated an imminent attack on Sackett's Harbor, and reported that Kingston now had a garrison of 6,000 or more British regulars. Even though Prévost soon returned to Lower Canada, and deserters and pro-American Canadian civilians reported that the true size of Kingston's garrison was 600 regulars and 1,400 militia, Chauncey and Dearborn chose to accept the earlier inflated figure. Furthermore, even after two brigades of troops under Brigadier General Zebulon Pike reinforced the troops at Sackett's Harbor after a gruelling winter march from Plattsburgh, the number of effective troops available to Dearborn fell far short of the 7,000 planned, mainly as a result of sickness and exposure. During March, Chauncey and Dearborn recommended to Armstrong that when the ice on the lake thawed, they should attack the less well-defended town of York instead of Kingston. Although York was the Provincial capital of Upper Canada, it was far less important than Kingston as a military objective. Historians such as John R. Elting