"We must fire the mines now!" Walter heard somebody say. "Fire them as closely together as possible, and then make for the starboard side amidships." This order had scarcely been given when the wires attached to the mines were touched off. A sullen roar from beneath the _Merrimac_ followed, and the vessel was thrown high up in the air, while great columns of water spouted up on every side. Then slowly but surely the collier began to sink. CHAPTER XVIII WALTER'S ADVENTURE ON SHORE Although the _Merrimac_ had been blown up and was sinking, the Spaniards continued to fire upon her without interruption, and as before, the air was filled with solid shot, bursting shells, and the whistling of leaden messengers from rapid-firing rifles. The order to gather at the starboard was a wise one, for this spot was the best protected on the deck, as the port side was settling rapidly. To take to a small boat or the catamaran would have been the height of foolishness, for a strong searchlight was being thrown on the scene, and the men would have been picked off by the Spanish gunners at will. With the others Walter rushed to starboard and found a hiding-place close to the rail. "I wonder what will happen next," he muttered. He was certain that something would take place very soon, for the waves of the harbor channel were already rolling over a portion of the _Merrimac's_ deck. A few anxious minutes passed, when suddenly the doomed collier gave a heavy list to starboard, and Walter found himself sliding along the rail and unable to stop himself. "Hold on!" shouted somebody. "Who is that?" Still weak, and with the flying spray drenching his face, Walter could not answer, and in a second more the questioner had disappeared amid the gloom, smoke, and flying water. Again came a lurch of the collier, and Walter was hurled flat and sent spinning against the smoke-stack. As he arose he saw Lieutenant Hobson and his men climbing over the starboard rail. Realizing, even in his bewildered state of mind, that he could not do better than to follow them, he, too, made for the rail, going over at one point as the courageous commander of the expedition went over at another. The crew were swimming for the catamaran, which had been shoved off from the _Merrimac's_ side, and Walter came after them. Hardly had the catamaran been gained, than, with a final lurch and quiver, the _Merrimac_ went down, partly across the narrow channel, but not exactly in the position in which she would have been placed had not the rudder chain been shot away. [Illustration: WITH A FINAL LURCH THE MERRIMAC WENT DOWN.] As the craft sank, a yell came from the Spanish battery nearest at hand, the gunners thinking they had sunk an American man-o'-war and not dreaming that the sinking had been done by those on board and purposely. But none of the Americans paid any attention to these cries, all thinking only of escape, now the work of the night was over.