A careful review of existing harbor charts convinced him that entry to the channel would need to take place at flood tide, passing close aboard the rocks directly below El Morro Castle, the deepest side of the channel. The narrowest point in the channel was 350 to 400 feet wide. On hand was the 3,000-ton collier USS Merrimac, which at 333 feet in length would serve the plan perfectly, and it was a ship the Navy could sacrifice without much detriment to the fleet. Ideally, the mission would require an evening when the moon would provide an hour of!ight as they navigated the channel entry, but then set behind the western bluff to furnish covering darkness as the ship approached the choke point; 2 June offered the best conditions. Hobson's training and naval constructor mind-set was instinctively focused on keeping ships afloat, but now he needed to use these same skills to sink one. He began by assessing the stresses and strains required to destroy key bottom plates and bulkheads,
USS Merrimac, 1898
and concluded that placing explosive devices outboard of the hull would be more effective than inside the hull. Charges inside the hull would require loosening hundreds of rivets. Given the rusty condition of Merrimac's hull, there was not enough rime to accomplish this tedious task and still meet the June deadline. Assessing rates of water flow through various sizes of exploded holes, Hobson determined that ten water-sealed canisters (torpedoes), each containing seventy-eight pounds of powder, "placed abreast bulkheads and cargo hatches" on the port side would do the job in just over a minute. The port side was chosen for placement of the charges because the ship would be making a sharp turn to port as it approached the designated point for sinking, and the rush
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1he Castillo de San Pedro de la Roca, also known as El Morro Castle, atop the cliffi at the entrance to Santiago Harbor, Cuba, was well-positioned to protect the harbor. Hobson and his men aboard the Merrimac would have to slip past this heavily armed fortress to get to the choke point in the channel.
of water into the hull would be increased by the turn. In addition, the weight of the explosives on the port side gave the ship a slight list in that direction, which would also increase the inflow of water. Hung from cables on the port side, twelve feet below the water line, each canister would be fired electrically in quick succession, starting at the bow and progressing aft, causing the ship to sink by the bow. Detonation would be triggered from the bridge by an "electro magnetic machine" (generator). Tons of water would be pumped into the collier's double bottom and every manhole and hatch cover removed or opened before she entered the harbor. To slow the ship and hold her in position at the choke point, anchors would be rigged over the side at water level, fore and aft, each secured by a rope hawser. When rhe ship was in the proper position, the crew would take an axe to the hawsers to let-go the anchors. To assure maximum explosive effect, Hobson suggested that the Merrimac's 2,300 tons of coal be removed from the ship; instead, the coal was merely shifred from the port to the starboard side. A detailed plot and timeline for Merrimac's projected movements was prepared. The ship would approach the channel entry
at top speed, steering midway between two US ships positioned just outside the entrance as guides. A rescue vessel, the armed yacht Hornet, would follow the Merrimac partway into the harbor opening. Approaching the channel, Merrimac would throttle back to five knots. When the "All Stop" order was given, crewmen below would open the seacocks to start the flooding. Upon reaching the choke point, the helmsman would steer "Hard-a-Pon" to swing the ship sharply and position it broadside across the narrowest part of the channel. Up forward, the starboard bow anchor would be let go, followed by the starboard anchor off the stern. The explosives would then be detonated. If the anchors failed to hold, it was expected that the impact of the explosions would cause the ship to settle fast enough to avoid the ebb tide moving Merrimac off the choke point. Hobson concluded that seven courageous, competent, and physically fit sailors could accomplish the mission: three Merrim1ac crewmen with knowledge of the ship's eng{ineering characteristics and shiphandlimg tendencies, and four petty officers frorrn the fleet. Competition for these positioms was intense, as commanding officers ~SEA
HISTORY 155, SUMMER 2016