But the Royal Navy was used to operating in shallow water. Many of its ships carried special high-frequency sonars that could provide almost picture-quality images of whatever lay on the bottom.
The German submarine was relying on three things to safeguard her from such sonars. First, her small size — barely one thousand tons surfaced — and minimal sonar cross section. Second, her anechoic coating and special hull design should help absorb and scatter enemy sonar pulses. Last, and most important of all, U-32 lay close beside the old wreck, almost hull-to-hull — hiding in the sonar and magnetic shadow cast by the larger vessel.
Ritter and his crew resigned themselves to a long stay on the bottom, breathing air that would grow fouler as the hours passed. Like a spider in its web, the U-32 lay in wait for her prey.
HMS Brecon led the outbound convoy heading for Gdansk. Built with a glass-reinforced plastic hull, and equipped with a pair of unmanned submersibles and a high-frequency sonar, the Hunt-class minehunter had proven her worth after the Falklands war by sweeping Argentine minefields laid off Port Stanley.
Now she plodded down the estuary at a sedate ten knots, sweeping back and forth. Behind her came two Type 22-class frigates, HMS Chatham and HMS London.
Three merchant ships followed the warships. A third frigate, HMS Argyll, a Type 23, brought up the rear.
Every warship was at action stations, expecting trouble. The three merchant ships, one bulk freighter and two container ships, held the better part of a British armored regiment, along with spare parts and ammunition.
U-32’s crew, lazing at their own duty stations, sat up as the first chirp of the enemy’s sonar beams came over the attack center speaker.
Ritter cocked his head toward the ceiling, listening as the British ships steaming overhead came closer.
The high-frequency chirping swelled, backed by the low, dull thrum of the minehunter’s engines. New sounds over the speaker signaled another British ship moving in behind the first.
Chatham’s active sonar made a deeper, duller noise than Brecon’s set.
More crewmen tensed as the sounds grew steadily louder. In theory, they were reasonably safe from detection. But theory seemed a poor substitute for certainty when the sonar pulses lashing the U-32 could be heard pinging through the hull itself.
Aboard Brecon, the senior petty officer manning the high-frequency sonar watched his screen carefully. He knew these waters well. The wreck, a coastal freighter sunk by Stukas in 1940, was a familiar landmark on his charts. He glanced at the digital clock above his display. They were right on time.
The wreck appeared, crawling down the screen as Brecon steamed toward it. He studied the bottom area around the sunken freighter closely. Nothing. Just the usual jumble of green-white shapes. Anything shaped like a submarine should have stood out clearly.
U-32’s sensitive sonar gear picked up machinery sounds emanating from the oncoming convoy and fed them to her fire control computers. By comparing the noises against prerecorded data sets, the computers were able to rapidly classify each ship. As always, information obtained during peacetime exercises was proving useful in war.
Ritter hovered over the computer display, watching the results of this automated search appear. Moving blips indicated seven ships sailing east in line, centered in the channel. His fingers drummed against the console. The three warships were tempting targets, but his instructions were clear. The merchantmen were his first priority.
“Prepare for an attack,” he ordered. “Two torpedoes at the lead merchant, three each at the other two.”
Every man in the boat held his breath as the ships drew nearer. The swishing roar of the enemy minehunter’s screws passed overhead and began to fade.
Ritter kept his eyes on the display, watching the six ships behind Brecon.
Bearing, still steady. Range, decreasing. He looked up at his diving officer. “Lift off.”
Valves opened, and a shot of compressed air entered U-32’s ballast tanks, changing her buoyancy from slightly negative to slightly positive. She lifted smoothly off the bottom. At the same time, her silent propellers spun up slowly, giving the submarine bare steerageway.
Once depth and speed were stabilized, the diving officer nodded silently to Ritter. They were in position.
The captain turned to the fire control officer. “Ready?”
“Solutions checked and valid.”
Ritter wrapped one hand around an overhead support and took a deep breath. Now. “Shoot!”
One after another, eight Seal 3 torpedoes, pushed out of their tubes by a pulse of water, came to life and sped toward their targets. Dual-core wires connected each torpedo to the U-32 and her fire control computer. These wires carried guidance commands from the sub to its weapons. They also allowed the sub to see everything its torpedoes saw.
With so many propellers thrashing the water, the British warships had failed to hear the German submarine as she vented her tanks and came off the bottom. But the high-pitched screw noises made by eight torpedoes screaming in at thirty-five knots were unmistakable.
In seconds, sonar plots aboard all three frigates showed their bearing and probable origin point. But it was too late.
The first torpedoes were already reaching their targets.
Van Dyck, a bulk freighter of twenty thousand tons deadweight, took one torpedo in the bow and another in the engine room. Although each Seal 3 carried a quarter ton of PBX, the vessel was only crippled, not destroyed. Within seconds she was practically dead in the water, listing to starboard. She would have to be towed back for repairs in Great Britain’s already overtaxed shipyards.
Three torpedoes slammed into Falmount Bay, a container ship of the same size. Without decoys, at slow speed, the large ship was an easy target. Three plumes of yellow-stained water and smoke fountained high into the air. Falmount Bay broke in half and sank.
Behind her, only two of three incoming Seals plowed into the container ship St. Louis.
The third missed and ran up the estuary until it ran out of fuel and drifted harmlessly into the mud. But she was smaller than the others and carried a flammable cargo. Internal explosions tore her apart in minutes — sending a huge plume of smoke high into the atmosphere.
Chatham and London raced for the old wreck, sonars blasting, pounding the estuary in a frenzied search. Argyll, in the rear, turned to assist the stricken Van Dyck. She also launched one of her two Westland Lynx helicopters to assist in the hunt.
Ritter didn’t waste time patting backs. Celebrating could come later — once he and his crew were safely back in port. “All ahead flank!”
U-32 was not silent now. Her only hope of escape lay in speed, and she had a lot of it in reserve — twenty-three knots submerged. She darted out from the wreck, right under Chatham as it charged in. That meant risking an over-the-side shot by the British ship’s triple torpedo mounts, but the closing speeds were so high that the frigate didn’t get a solid fix on her until it was too late.
The German sub skipper divided his attention between the sonar display and the plot. Every minute spent at full speed cost him five hours’ worth of battery charge. Like all conventional submarine captains, he had to constantly weigh the advantages of speed with the risks of running out of power.