Upon the declaration of war on April 6th, the fleet was at once mobilized and a flotilla of destroyers was equipped for foreign service and sent overseas, where the first contingent arrived at a British port on May 4th, 1917. The second reached Queenstown on May 13th, and before the end of the month both were engaged in the work of hunting submarines in coöperation with the British and French navies. Early in June units of the naval aeronautical corps landed upon French shores and inside another month the vanguard of the American Expeditionary Forces, convoyed by the Navy, arrived in France. Battleships and cruisers quickly followed the destroyers across the ocean and took their places with the British Grand Fleet, on watch for the appearance of the German navy from behind its defenses at Heligoland. While it was thus quickly making itself felt in the prosecution of the war, the Navy Department at once entered upon a great program of development, expansion and training. It had in commission when war was declared 197 vessels. When the armistice was signed there were 2,000 ships in its service. In the same time its personnel had expanded from 65,777 to a total of 497,000. In addition to the cruisers and battleships on the ways, 800 smaller craft were built or put under construction during our nineteen months of war. Formerly the building of a destroyer required about two years. But the great importance of that type of vessel and the urgent need for more of them speeded production to the fastest possible pace and at the end of the war destroyers were being built in eight months and in some cases in even less time. In one instance a destroyer, the Ward, at the Mare Island Navy Yard, was launched in seventeen and one-half days from the laying of its keel and within seventy days was in commission. The end of the war found the American Navy with more destroyers in service or under construction than the navies of any two nations had possessed before the outbreak of the war in 1914. In the first nine months of 1918 there were launched 83 destroyers, as against 62 during the entire nine preceding years.