Mack decided to take a huge gamble. Calling his navigators and officers into the wardroom, he announced that they were going to give up trying to pick up the Yankee near the Denmark Strait. Instead, Mack was going to try to guess where the Yankee was headed next, and he wanted to try to beat her to her destination. Now Mack, his XO Charles H. Brickell Jr., the engineer officer Ralph L. Tindal, and others bent over charts and began an intense game of "what if," putting themselves in the place of the Yankee's commander. Desperation weighed in as much as logic when they finally decided to attempt to pick up the Yankee's track several hundred miles south, near Portugal's Azores Islands.
Lapon hurried down there and then trolled about the appointed spot for three days. Too much time, Mack fretted. He made another guess and moved the sub west. Almost as soon as Lapon settled into her new patrol, her hull began to reverberate with the grinding of metal on metal. Mack came running into the control room. The diving officer reported that Lapon was losing depth.
The 4,800-ton Lapon had been caught in the net of a deep-sea fishing trawler, tangled in the net's metal weights and thick metal cable. The Yankee could pass by at any moment, and Lapon was dangling along with Sunday brunch.
It didn't take long for the fishermen to give up, or maybe they cut their net. Either way, they left the area with the greatest one-that-gotaway story of their lives. But a piece of the trawler's cable had worked its way around a sonar device on the front of the submarine. There was no way Lapon could effect a silent trail with the dangling cable clicking across her bow.
Mack had no choice. He waited for dark, then ordered Lapon to the surface. Now praying that the Yankee would not pass, at least not now, he sent a man out onto the sail with a large pair of bolt cutters. His gamble worked-the cable was away and Lapon was ready when the Yankee showed up twelve hours later.
This time Mack was determined not to lose the Soviet submarine. This more southern portion of the Atlantic wasn't as loud as the waters off Greenland, but the Yankee was still quieter than any submarine a U.S. boat had ever tried to follow. It was time for a new tactic that Mack dubbed on the spot the "close-in trail." Lapon would tailgate the Yankee, moving no further than 3,000 yards away. More than 4,000 or 5,000 yards away, and the Yankee would be lost.
Mack's strategy was risky. Hurtling 4,800 tons that close to the massive Yankee was dangerous. Normally even surface ships try to stay about two miles apart for fear of collision. And Lapon had the added worry of detection. Mack just hoped that this new submarine didn't have better sonar than her predecessors. Lapon was so close that all someone had to do was drop a piece of equipment or slam a watertight door at the wrong time and even the Soviets' outdated equipment could register an American shadow.
Just about everyone on board realized the risk they were taking, but nobody dared question Mack. Nobody had time to. It had become crucial now to figure out what the Soviet vessel sounded like when she slowed down, or turned. Until Lapon's sonar team could figure out what combination of clicks or tones matched which maneuvers, both submarines were in grave danger of colliding.
Mack ordered Lapon to slip side to side behind the Yankee as his men set about finding answers to a matrix of questions. Once again, Mack engaged himself in a game of "what if," trying to put himself in the Soviet captain's place, wondering what he would do, and when. It was like working on a very large, very difficult crossword puzzle. One answer led to others. One blank created several avenues of confusion. All Lapon's crew could do was keep collecting information. The sonar teams began listening for any flaws in the Yankee's construction, anything that would give them clues to help them "see" the other submarine as it maneuvered.
Standard sonar would never have been enough. The Yankee was simply too quiet. But Lapon wasn't relying on just standard sonar. Mack had slipped aboard an added edge, an experimental sonar device designed to capitalize on some discoveries that Kelln's USS Ray had made in 1967 and 1968 when she trailed the November-class attack sub into the Mediterranean and then tracked a Charlie in the North Atlantic. The device worked by upgrading the way the standard system registered noise levels in the ocean. It zeroed in on certain tones, those made by the Yankee as she moved through the water, almost the way notes of music sound from a bottle when somebody blows over the top. After a fair amount of trial and error, Lapon's crew realized that one particular frequency changed each time the Yankee turned. A shift to the left, and the tone was slightly higher. When the Yankee moved away, the tone lowered. If the tone changed quickly, it meant the Yankee was making a swift course change.
The one place Lapon couldn't follow from was directly behind. Unlike other Soviet submarines that offered an easy-to-follow din from their propellers, the Yankee was quiet enough from behind that she was rendered effectively invisible. Indeed, the Yankee might have been able to slip away entirely, even with Lapon's extra sonar gadget, if not for what must have been a structural flaw. To the left, the Yankee's machinery was making more noise than any other portion of the boat.
From now on, Lapon was going to follow that machinery noise. If it got louder, Mack would know that the Yankee had made a left turn. If the Yankee seemed to vanish, she probably had turned right.
Ultimately the best vantage point turned out to be a little off to the side of the Yankee's stern, in either direction-with the left side being a little louder. From there the new sonar device picked up strong tones, and standard sonar registered steam noises coming from the Yankee's turbines and the clicks made by the Yankee's propeller each time it made a revolution. Counting those clicks and logging turn counts was how Mack and his crew determined the Yankee's speed.
All this took four or five days to figure out-longer than the entire length of most trailings attempted so far against the noisy Soviet Hotel, Echo, and November subs, the HENs. But Mack wasn't going to break off. Instead, he was going to keep following, and he would figure out the mechanics as he went along. The process of trial and error spanned several watch stations, leaving it up to Mack and his engineer officer to teach each succeeding team what had been discovered over the past twelve hours.
Mack was determined not to lose the Yankee again, especially when he realized that she was headed on a track toward the U.S. Atlantic coast. He again began to forgo sleep, although he slipped in 15-minute catnaps at the helm, a trick he picked up in college from an article in Reader's Digest.
Days later, Lapon was still tracking the Yankee. Mack began to map out the Yankee's operating area, one of the most crucial pieces of intelligence he could carry home. The Soviets had settled into a holding pattern that covered about 200,000 square miles. They moved back and forth, staying between 1,500 and 2,000 miles off the United States.
Up until now, the Navy had been convinced that the Soviet Union would send its Yankees as close as 700 miles from U.S. shores. But Mack's discovery would help Naval Intelligence determine that the Yankee's new SS-N-6 missiles actually had a range of 1,200-1,300 miles.
If Lapon had not followed the Yankee this far, it would have been difficult for the United States to keep track of the new Soviet nuclear threat, even though the Yankee plowed through what appeared to be a well-defined box. The United States would have been searching 800 miles too close to shore.
Now Mack mapped the Yankee's exact course. Choosing one area, she meandered at about 6 knots before racing to another area at 12–16 knots. Then she slowed again. Every 90 minutes, almost to the second, the Yankee changed course. Sometimes by 60 degrees, sometimes by far more.