The revolt of the American colonies, which rose in this year to the importance of a national war, was soon to furnish him with objects worthy of his skill and courage. On the 10th of May the Americans surprised Ticonderoga, and, having secured the command of Lake Champlain by a strong squadron, were enabled to prosecute offensive operations against Canada. Sir Guy Carleton, the governor and commander-in-chief of that province, had very inadequate means to defend it. The enemy took Montreal, and in the beginning of December laid siege to Quebec, expecting an easy conquest; but their commander, General Montgomery, who had summoned Sir Guy Carleton in the most arrogant and threatening style, was killed on the 31st, in attempting to storm the place, and his troops were repulsed. The siege, however, was continued by Arnold, till Commodore Sir Charles Douglas, in the _Isis_, with two other ships under his Orders, forced his way through the ice, much before the season at which the river is usually open. His appearance drove the besiegers to a hasty flight, in which they suffered such extreme privations, especially their sick and wounded, that General Carleton most humanely issued a proclamation, in which he ordered them to be treated as fellow-creatures in distress; and encouraged them to claim the offered hospitality, by assuring them that they should be unconditionally liberated as soon as they were able to return home. At the same time, with energy equal to his humanity, he hastened to complete the deliverance of the province. Additional reinforcements which reached him in the spring enabled him to give the enemy a final defeat at Trois Rivieres in June, and then to take measures for wresting from them the command of Lake Champlain; an object essential to the security of Canada, as well as to prosecuting offensive operations against the New England States. Lake Champlain is a long narrow lake to the N.E. of Ontario, communicating with the St. Lawrence a few miles below Montreal by the river Chamblee, or Sorel. It is nowhere more than eighteen miles across, and its average breadth does not exceed five. Below Crown Point it is a mere channel for ten or twelve miles to its southern extremity at Ticonderoga. Here it receives the waters from a small lake to the southward, Lake George, but the communication, as well as that with the St. Lawrence, is interrupted by shoals and rapids. From Lake George to the Hudson is only six or eight miles, the sole interruption to a water frontier from the St. Lawrence to New York, navigable for vessels of burden for four-fifths of its length, and for bateaux nearly all the way. The command of this line would enable the northern and southern armies to co-operate effectually; to press on the New England States along their whole border; to cut off all communication between them and the rest of the Union, and to prevent any hostile attempt on Canada.