Admiral William T. Sampson, the commander of America’s fleet in Cuba, ordered a blockade of the entrance into Santiago Bay and the city of Santiago. He wanted to trap the Spanish fleet stationed in the bay and isolate the Spanish army defending the city. Thus trapped, Spanish warships could not threaten the planned nearby landing of American troops. To accomplish his goal, Sampson wanted to sink one of his colliers (coal ships) in the bay’s narrow, shallow channel. He chose a ship with chronic engine problems, the Merrimac.

Sampson ordered Lieutenant Richard P. Hobson to lead the mission. Hobson daringly planned to position the Merrimac at the channel’s narrowest point, between two heavily-armed Spanish forts. His crew would drop anchor on one end of the ship, let the tide swing it lengthwise, and then sink the vessel with electronically-rigged torpedoes. After the crew detonated the torpedoes, they were to dive off the Merrimac, swim to a small catamaran, and slip away. Any ship trying to pass would strike the sunken vessel.

Hobson needed six skilled and brave sailors to execute this dangerous mission. He chose Deignan among the many volunteers. Deignan later wrote that he volunteered for this hazardous duty because of his mother. Mrs. Deignan had had a hard life and that if he did not return home, the United States would never let her suffer as long as she lived.

Hobson’s plan unfortunately went awry. As the Merrimac approached the channel in the night, the Spanish detected the 5,000-ton ship and shot out the collier’s steering mechanism. Deignan’s job of maneuvering the ship into its precise blocking position became impossible. The crew nonetheless persevered, bravely enduring murderous fire, and proceeded to sink their ship as planned, but not in the planned place. Deignan later said that time on the Merrimac seemed like the longest period of his life.

After exploding the torpedoes as planned, the Americans abandoned their ship, swam for the catamaran, and stayed in the water while holding onto its side. They did not dare to climb on board and risk being shot by the Spanish. By daylight the crew was captured, the only American military personnel held prisoner by the Spanish during the war. Admiral Pascual Cervera, impressed with the bravery of the American sailors, treated his prisoners well. They stayed in the Morro Castle for about a month. A prisoner exchange occurred before the Spanish troops in Santiago capitulated. Theodore Roosevelt and John Jacob Astor, an influential American and regimental commander led the exchange negotiations.

Talking to a reporter shortly after his release from the Spanish, Deignan described the harrowing moments before abandoning the ship.

“We all lay on the deck, packed like sardines in a box, with shots flying about our heads, expecting every minute to be killed.” About four o’clock [a.m.], “our vessel gave a list to starboard. . . Lieutenant Hobson, when he saw she was sinking, said, ‘Very Good! They are helping us out; they are doing it for us.’ . . . At this time the water was pouring in over the starboard rail, coming down on us, when we scrambled to our feet and seized the rail to prevent being washed into the hold. The ship then gave a list to port, the water coming over our port rail. . . We all leaped overboard and swam for the catamaran, which was floating near the ship’s side. Just as we started for it the Merrimac sank, and the suction drew us down with her under the water.”

Deignan and all of the crew, including Hobson, were awarded the Medal of Honor.