Admiral Sampson arrived off Santiago June 1st, and assumed direct command of the squadron. The blockade, which lasted for over a month, was eagerly watched by the whole American people. The most thrilling incident was the daring but unsuccessful attempt made by Lieutenant Richmond Pearson Hobson to sink the collier Merrimac across the entrance to Santiago harbor, undertaken by direction of Admiral Sampson. Electric torpedoes were attached to the hull of the ship, sea-valves were cut, and anchor chains arranged on deck so that she could be brought to a sudden stop. Early on the morning of June 3d, Hobson, assisted by a crew of seven seamen, took the collier into the entrance of the harbor under heavy fire and sunk her. The unfortunate shooting away of her steering-gear and the failure of some of the torpedoes to explode kept the ship from sinking at the place selected, so that the plan miscarried. Hobson and his men escaped death as by a miracle, but fell into the hands of the Spaniards.[280] II THE LAND CAMPAIGN As soon as Cervera was blockaded in Santiago and the government was satisfied that all his ships were with him, it was decided to send an army to co-operate with the navy. Hitherto the war had been a naval war exclusively, and the two hundred thousand volunteers who had responded to the calls of the President in May had been kept in camp in different parts of the country. Most of the regular infantry and cavalry, together with several volunteer regiments, had been assembled at Tampa and organized as the Fifth Army Corps, in readiness to land in Cuba as soon as the navy had cleared the way. Conspicuous among these troops was the First Volunteer Cavalry, popularly known as Roosevelt’s Rough Riders, a regiment which through the energetic efforts of Dr. Leonard Wood, an army surgeon, who became its colonel, and Theodore Roosevelt, who resigned the position of assistant secretary of the navy to become its lieutenant-colonel, had been enlisted, officered, and equipped in fifty days. It was recruited largely from Arizona, New Mexico, and Oklahoma, and had in its ranks cowboys, hunters, ranchmen, and more than one hundred and sixty full-blooded Indians, together with a few graduates of Harvard, Yale, and other Eastern colleges.