Straits of Power

keystone was to do the last thing the Axis expected. This was why Jeffrey was fighting the outgoing tide.

Most of the Mediterranean Sea had very little tidal range; from low to high was only a foot — almost nothing. But the Strait of Gibraltar was different. The tides through the narrow gap ran very strong.

The wind-driven prevailing surface current flowed into the Med from the Atlantic. The surface current was offset by another one underneath. This balancing countercurrent flowed steadily outward, from the Med toward the Atlantic.

When the tide flowed into the Med, it intensified the inward prevailing surface current’s speed. This is what any sailor would expect; it’s common sense.

But when the tide flowed out of the Med, peculiar things happened. At shallower depth, the outflow would be strong along both shorelines of the Strait. Yet in the middle of the Strait, contradicting the outgoing tide, the water down to about 150 feet still flowed inward. All these different currents and tides could run as powerfully as four knots.

When water at one temperature and with one salinity level flowed one way, and adjacent water at a different temperature and salinity flowed the opposite way, extremely chaotic eddies and gyres resulted. This badly garbled local sound propagation. And the outward tide ran at a different speed from the deep, outgoing current; where they touched, one sliding over the other, fluid shear and friction made acoustic conditions even worse.

The sonar speakers confirmed what Jeffrey knew. The gurgling, swishing sounds picked up from all around were uneven, jagged, unsettling. They were much louder than Challenger’s or Ohio’s flow noise would ever be at this speed.

Jeffrey’s task group was using this. Instead of riding an incoming tide — with the ship’s propulsion very slow for total quieting, an old submariner trick—Challenger and Ohio followed a route through the maximum turbulence ever available here. They hugged the southern boundary between the outgoing tide and the incoming shallow current, at the depth where the outgoing deep countercurrent began. Water to port ran westward. Water to starboard ran east. Colder, saltier water beneath the keel ran westward too, but not as fast.

Jeffrey was depending on this turbulence for acoustic concealment. It gave him and Parcelli a fighting chance to be missed by Axis hydrophones of many different varieties, on guard for movement through the Strait by Allied subs.

And staying relatively shallow, but not too shallow, provides several other benefits — though the effect on our odds of survival is rather mixed.

Both subs were below the keels of all but the deepest-draft surface ships; laden supertankers could reach down over 100 feet. Supertankers inbound here should be empty except for ballast, and riding high. It was the outbound ones full of oil, heading from the Middle East to neutral countries like Sweden or Finland, that were accidental submarine killers. By keeping to the south in the Strait, Jeffrey intentionally stayed at the edge of the inbound lane of the shipping traffic-separation scheme. But merchant mariners were notorious for sloppy navigation and for ignoring the rules of the road. Anything could happen.

Then there was the problem of mines. There weren’t supposed to be any in the Strait itself, and the surface traffic in front of the task group served willy-nilly as minesweepers. But a moored mine somewhere in the Med — or protecting the Axis fortress at Gibraltar — might have broken loose and drifted into their path, without being set off for them by some unfortunate merchie. Challenger and Ohio had off-board probes designed to hunt for mines, but these couldn’t be deployed. They were too slow to keep up with their parent subs at thirteen knots, and their active sonars wouldn’t work well in such acoustic turbulence — while any pings from them could betray the task group’s presence.

It occurred to Jeffrey that the Axis had probes and military ocean rovers too. Ohio or Challenger might crash into one and suffer serious damage. The noise of the crash could be loud enough to get noticed. The loss of signals from their probe would surely alert the enemy to investigate more closely — that was the whole point of using rovers for ASW patrols, and of cultivating an ASW commander’s mind-set of vigilant paranoia.

And while cruising at only 150 feet with their sonars underperforming, an enemy helo with dipping LIDAR might see Challenger’s or Ohio’s hull before they had any chance to react and defend themselves.

Milgrom announced another surface contact on the bow sphere. Since this new contact was ahead of them, it was slow: Challenger was overtaking.

Jeffrey watched the contact icon pop onto the tactical plot. The icon indicated an unknown vessel type and nationality. Jeffrey didn’t like this.

Milgrom’s people identified the vessel as a merchant ship.

The icon was updated. Jeffrey began to hear the ship on the speakers. Her screws swished and churned in a manner different from the current-boundary turbulence. She hissed and pounded as her hull cut through the water and met each swell. Then Jeffrey could hear mechanical growling and throbbing from the big diesel engines that modern merchants used instead of steam, and he listened to the humming of her auxiliary machinery. The sounds died abruptly in Challenger’s baffles.

The way that ship’s noise stopped so suddenly reminded Jeffrey of one of his other tactical problems. Because of the close proximity of Jeffrey’s and Parcelli’s subs, plus the bad sonar conditions and the vicious eddies and gyres, only Ohio, aft of Challenger, trailed a towed array. To avoid leaving the area of highest water disturbance — and thus become more exposed — neither sub would circle to do a baffles check in the Strait.

Challenger was blind to her stern, with Ohio acting as Jeffrey’s seeing-eye dog. They would learn soon the hard way if he’d made a wrong decision on this. Ohio’s towed array wouldn’t work well in such troubled waters, and might even snap or be cut at its root by her screw as Ohio dipped and bucked. Plus, when she did make a detection, she needed to send Jeffrey a report via the acoustic link — which could go out at any time.

Long minutes passed. A German destroyer went by from behind, heading inward, then another, presumably returning from the engagement with Dreadnought and Texas. Their hull-mounted active sonars pinged, setting Jeffrey’s every nerve on fire. The Germans acted as if they didn’t notice him, but that might be a trick, to lure his task group farther in to be bottled up and clobbered. Military aircraft overflights were detected faintly; no incoming weapons materialized, at least not yet.

“Enemy’s Gibraltar base off our port bow,” Sessions announced. “Closest point of approach in ten minutes.”

Jeffrey and his crew hunkered down. Gibraltar sat on the north side at the inner end of the Strait, its famous Rock on a long peninsula enclosing the massively defended harbor within a bay. Parcelli’s weapons officer would have his giant battery of Tomahawks pretargeted at Gibraltar now. In an emergency, the task group might wreak enough havoc to battle their way back to the Atlantic — or go down in a blaze of useless glory. The air in the control room kept getting stuffier and stuffier.

Chapter 27

Fresh from a full meal and a catnap, Egon Schneider exercised his privilege as captain of Grand Admiral Doenitz and took a long, hot shower. So far, he was satisfied with the performance of his new ship and his crew.

He dressed in a black jumpsuit and seaboots, and strode into his control room. A junior officer had the conn. Schneider’s einzvo, Manfred Knipp, kept an eye on things. Schneider read different displays, to update himself on the overall situation.

“I have the conn,” he announced. Acknowledgments were duly made, the junior officer vacated his seat, and Schneider sat down at the command console. The control-room lighting was red; it was nighttime on the surface.

Schneider’s trip through the whole South Atlantic Ocean at sixty knots had gone well. Doenitz’s sonar men performed repeated self-noise checks using the arrays mounted