SSN

    Each Mk 48 was wire guided so that targeting data during the initial stages of the torpedo launch could be transmitted back and forth from the Mk 48 to the BSY-1 fire-control system on board the attack submarine. During the terminal stages of the attack, the Mk 48 would use its powerful active seeker to detect, home in on, and then destroy its target. As long as the wire was intact, information from the torpedo was constantly relayed to Cheyenne until detonation.

    After the meeting, Mack returned to the control room. Knowing that there might be a nuclear attack submarine in the area, he ordered that instead of running at twenty-six knots for much of the way to Pearl Harbor, as he had originally planned, Cheyenne would now slow more frequently in order to listen to her surroundings. This "sprint and drift" technique was one of the best methods of arriving at a destination quickly while also allowing the submarine's passive sonar to search for any possible sonar contacts.

    Cheyenne was now at an ordered depth of four hundred feet. At this depth, she was in her own element, that of the depths of the ocean. If necessary, she could still be reached by the relatively new, albeit slow, ELF, or extremely low frequency, band of communications. If there were a dire emergency, or a change in her orders, Cheyenne would be instructed by a short, coded ELF message to come to communications depth in order to receive important message traffic.

    Running at twenty-six knots was not always quiet. The screw, known to those outside the Navy as a propeller, was working feverishly to propel the submarine at this speed. If too shallow, this created tiny air bubbles, which made a popping noise when they collapsed. This noise was known as cavitation and could give away a submarine's presence in the area. At this moment, Mack did not care as much about his stealth capability as he did about two other concerns: locating the submarine that was lurking dangerously near the West Coast, and arriving at the Pearl Harbor Naval Submarine Base with Cheyenne intact.

    All aboard Cheyenne were aware that they were making slight cavitation noise and that anyone who was close enough and quiet enough could determine their location. The frequent slowing and so-called clearing of the baffles, the normally "sonar blind" area astern of submarines, evened the score somewhat.

    At 1100 on 12 August, just ten hours after leaving San Diego, the OOD ordered Cheyenne to slow to one-third. Exactly eleven minutes later the sonar room came alive as Cheyenne slowed and her course was changed toward the north.

    "Tonal contact, center bearing 187 on the end-fire beam," called one of the young sonar operators. The consoles, which looked like computer screens with green lines running through them, were often the sonar operator's most important ally.

    An instant later the sonar supervisor, who had been paying close attention to the goings-on in this important center of the submarine, called to the captain, "Conn, sonar, we have a possible submarine contact bearing 187. We're only receiving blade rate information so far."

    Mack entered the sonar room, joining the five other men already there-including the sonar supervisor and the sonar officer. Everyone in the room knew that there was the possibility of encountering a Chinese submarine, but also knew it was highly unlikely. Chinese naval vessels rarely ventured this far away from home waters. This was especially true of the Chinese submarine fleet, which consisted largely of older-model diesel boats with just a few very noisy nuclear-powered attack submarines of the Han class.

    If there was a Chinese submarine patrolling off the West Coast of the United States, however, Mack was fairly sure that it would have to be a Han class. Naval intelligence reports had repeatedly explained that only one type of submarine was capable of travelling this far from Chinese home waters and operating-without surfacing-for an extended period of time. That type was a nuclear submarine, and the only Chinese SSN currently in service was the Han class.