On Lake Ontario the fortune of war was more equally divided. The Americans had been gradually collecting a naval squadron at Sackett's Harbour and had gained command of the lake as early as November, 1812. The command was, however, precarious, since it might be disturbed by the arrival or construction of new warships. One such was building at York, now known as Toronto, the capital of Upper Canada, when, on April 27, 1813, the American squadron under Commodore Chauncey attacked the town and succeeded in landing a detachment of troops under General Dearborn. The British general, Sheaffe, withdrew his regular forces from the town without awaiting an assault, but not before he had destroyed the ship of which the enemy were in quest. The Americans captured some naval stores, but did not attempt to hold the town; they set an evil precedent, however, by burning the parliament house and other public buildings before evacuating the place. On May 27 Chauncey co-operated again with Dearborn in an attack on Fort George, the capture of which threw the whole line of the Niagara into American hands. On the same day Prevost, whose naval strength had been reinforced, availing himself of Chauncey's absence, made an attack on Sackett's Harbour. The attack, which was renewed on the 29th, was miserably conducted, and ended in failure, though the Americans were compelled to burn the naval stores captured at York. The reinforcements had, however, transferred to the British the command of the lake, which was not challenged again till the end of July. Meanwhile their land forces were not idle. On June 6 the Americans were surprised by Colonel Vincent at Burlington Heights and over 100 prisoners, including two brigadier-generals, were taken. This defeat, combined with the approach of the British naval squadron under Sir James Yeo, induced Dearborn to abandon his other posts on the Canadian side of the Niagara and to concentrate at Fort George, but on the 24th another surprise ended in the surrender of a detachment of more than 500 Americans to a force of fifty British troops and 240 Indians. By the end of July Chauncey's squadron was once more strong enough to put to sea. It raided York on the 31st, but did not venture to join battle with Yeo; though a skirmish on August 10 enabled Yeo to capture two schooners.