But the long period of peace was now to be rudely interrupted, and the complications that followed the annexation of Texas at last brought on hostilities with Mexico. The possibility of this war had been long foreseen by the Government, and the navy was found prepared for it. For several years a squadron had been maintained on the western coast of America, from Valparaiso to the Columbia River; and at the declaration of war, May 12, 1846, a considerable force was assembled in the northern cruising-ground. A still stronger force, composing the Home Squadron, was concentrated in the Gulf. The two coasts continued during the war to be two distinct bases of operation; but as the Mexicans had no naval force, the operations consisted mainly in blockade, and in attacks upon the cities along the coast. Of the officers who held successively the chief command on the western coast, Commodore Stockton had the largest share of the work. Commodore Sloat, who was in command of the station when the war broke out, was there only long enough to make a beginning. This he did promptly and well. He had with him the frigate "Savannah" as flagship; the sloops "Portsmouth," "Warren," "Levant," and "Cyane;" the schooner "Shark;" and the storeship "Erie." These were all sailing-ships. At this time the coast south of the forty-second parallel of latitude, including the whole of California, belonged to Mexico, that parallel having been the boundary of the United States as fixed by the treaty of cession of Louisiana in 1803. North of this point was the unsettled and hardly-organized territory of Oregon. The squadron was therefore without a base of supplies in the Pacific, and as it took months to communicate with Washington, its commander was obliged to act largely on his own responsibility. The enemy's coast, including the peninsula of lower California, extended over four thousand miles. To cover such a range of coast even with steamers would require uncommon activity; and with a force of half a dozen sailing-vessels the task was much more difficult. Commodore Sloat's instructions of the 24th of June, 1845, which were written a year before the war broke out, contained these words:-- "It is the earnest desire of the President to pursue the policy of peace; and he is anxious that you and every part of your squadron should be assiduously careful to avoid any act of aggression. Should Mexico, however, be resolutely bent on hostilities, you will be mindful to protect the persons and interests of citizens of the United States near your station; and should you ascertain beyond a doubt that the Mexican Government has declared war against us, you will at once employ the forces under your command to the best advantage."