Terminal Run

In the red-lantern-lit hold, the two divers strapped masks around their necks and adjusted their tanks. The Mark 17 High Thrust Underwater Vehicle hummed with the power of her fuel cells. The commander of the mission climbed into the front, his chief petty officer climbing into the aft seat. When the checklist was completed, the two men put their faces into their masks. The lights in the hold shifted from a dim red glow to complete darkness. The trawler’s support crew shut the overhead hatch, sealing the pressure-tight hold. The HTUV inclined to a steep down-angle as the rail launching system prepared to eject them from the hold. The door in the keel opened slowly until the noise of the wake roared below them. The Mark 17 suddenly moved, catapulted down the inclined rails and splashing into the water, diving beneath the surface, the roar of the trawler’s screws overhead made more violent by their own thruster coming to full power.

The lieutenant who sat in the forward seat cranked the throttle of the motorcycle-style controls, pushing the Mark 17’s yoke down, accelerating the vehicle in a steep dive. The noise of the surface faded astern as they sank deeper, the engines becoming quiet as the craft leveled off at eighty feet below the waves. The lieutenant shivered as he engaged the computer pilot. The Mark 17 would wait at this depth, with a small buoyant wire antenna drifting upward to the surface to keep them in touch with the trawler and allow the computer to target the larger, swifter submarine during the upcoming rendezvous.

As soon as the towed array had made a tentative detection, the trawler captain had sent an E-mail message requesting transmission repair parts for his starboard diesel. Within five minutes an ELF transmission, Extremely Low Frequency, was made from the huge radio towers in Tsing Tao, White China, transmitting only two characters, the letters A and X. ELF radio waves were clumsy and nearly useless. It took ten minutes to transmit a single alphanumeric character and an enormous amount of transmitting power. But they did one thing no other electromagnetic signal could — they penetrated deeply into the ocean. The letter A began to transmit, the waves of the ELF signal carrying past the Mark 17 HTUV and its occupants to the depths of the sea, eventually striking the ELF loop antenna of the United States submarine Leopard, the loop mast retracted in the sail. The Leopard was steaming at 546 feet keel depth on course one seven five at fifteen knots, much too deep and fast for the Mark 17 to intercept her. But as the submarine’s radio equipment began to realize that the letter A was the first character of that day’s ELF call sign an alarm rang in the radio room and in the control room. By the time the letter X began to transmit, a phone call was placed from the control room to the captain’s stateroom, and George Dixon, Commander, U.S. Navy, was awakened with the word that there was a communications emergency, and that Leopard had been urgently called to periscope depth.