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Tolbert. It was the random icebergs scattered throughout the Marginal Ice Zone. Over three thousand icebergs were produced each year in the Barents Sea, breaking off glaciers on Svalbard, Franz Josef Land, and Novaja Zemlja, accompanied by the calving of glaciers on the east coast of Greenland. Most of the icebergs were small, but the larger ones descended several hundred feet, occasionally deep enough to ground on the bottom of the shallow Barents Sea.
    Tolbert called to his Weapons Officer, Lieutenant Mark Livingston. “Officer of the Deck, set the Arctic Routine.”
    Livingston repeated back the order and issued commands to his watch section. After settling in behind Yury Dolgoruky, Tolbert had returned North Dakota to a normal watch section rotation, with each watch augmented with a Section Tracking Party comprised of an additional fire control technician to monitor the plots, a Contact Manager, and a Junior Officer of the Deck. By setting the Arctic Routine, Tolbert had ordered additional sonar consoles manned and the Deck and Conn split, with Tolbert and the XO alternating as the Conning Officer.
    After a briefing from the Weps, Tolbert relieved him of the Conn, announcing to watchstanders in Control, “The Captain has the Conn, Lieutenant Livingston retains the Deck.”
    The Quartermaster acknowledged and continued preparations for entering the Marginal Ice Zone. He energized the submarine’s topsounder and fathometer. The topsounder would send sonar pings up from one of four hydrophones mounted on top of North Dakota ’s hull: two on the sail and one each on the bow and stern. The topsounder would detect ice above and provide warning if an ice keel descended toward them. To help avoid the occasional small iceberg, North Dakota would run deep, closer to the bottom than usual, using the fathometer to ensure they didn’t run aground.
    One of the sonar watchstanders shifted consoles, preparing to energize North Dakota ’s High Frequency Array, the forward-looking under-ice sonar mounted in the front of the sail, which would detect ice formations ahead. The sonar technician entered the requisite commands, bringing the console on-line, then cast furtive glances toward the ship’s Captain.
    Tolbert knew what he was thinking. North Dakota ’s topsounder and fathometer weren’t detectable, emitting narrow high-frequency beams that bounced back to North Dakota after reflecting off the ocean’s surface or bottom. That was not the case with the High Frequency Array, which sent pulses out in front of the submarine. Having set the Arctic Routine, Tolbert had to make the decision he’d been putting off—whether to energize the under-ice sonar and risk being detected.
    Commander Tolbert announced his decision. “Attention in Control. We will not use our under-ice sonar. We’ll let the Russians pick a path through the Marginal Ice Zone, and follow directly behind. Carry on.”
    Tolbert added, “Pilot, come to course three-five-five.”
    The Pilot entered the new course and North Dakota turned slightly left. Tolbert had been trailing the Russian submarine with an offset to starboard, but needed to trail directly behind while in the Marginal Ice Zone.
    After North Dakota eased into position behind the Russian submarine, Tolbert turned back to the north. Moments later, the Quartermaster looked up from the electronic chart and announced, “Entering the Marginal Ice Zone.”

 
    7
    MARGINAL ICE ZONE
    YURY DOLGORUKY
    Yury Dolgoruky continued her steady trek north at ten knots. Thus far, the topsounder had detected only sporadic chunks of sea ice floating above them, while the bottomsounder reported the smooth, shallow bottom of the Barents Sea, averaging only 230 meters in depth. However, Stepanov was focused on Dolgoruky ’s Ice-Detection Sonar display, which displayed objects in front of them as a colored blotch. Different colors represented the intensity of the sonar return, with red indicating a large, deep, or dense