The fog grew dense, so much so that at 7:15 A.M. Schwieger ordered a dive to U-20’s customary cruising depth, 72 feet. The depth was great enough to ensure that U-20 would pass underneath vessels of even the deepest draft. This was prudent practice, for U-boats, despite their fearsome reputation, were fragile vessels, complex and primitive at the same time.
Men served as ballast. In order to quickly level or “dress” his boat, or speed a dive, Schwieger would order crewmen to run to the bow or the stern. The chaos might at first seem funny, like something from one of the new Keystone Cops films, except for the fact that these maneuvers were executed typically at moments of peril. U-boats were so sensitive to changes in load that the mere launch of a torpedo required men to shift location to compensate for the sudden loss of weight.
The boats were prone to accident. They were packed with complicated mechanical systems for steering, diving, ascending, and regulating pressure. Amid all this were wedged torpedoes, grenades, and artillery shells. Along the bottom of the hull lay the boat’s array of batteries, filled with sulfuric acid, which upon contact with seawater produced deadly chlorine gas. In this environment, simple errors could, and did, lead to catastrophe.
One boat, U-3, sank on its maiden voyage. When it was about two miles from the naval yard, its captain ordered a trial dive. Everything seemed fine, until the deck of the U-boat passed below the surface and water began pouring into the boat through a pipe used for ventilation.
The boat sank by the stern. The captain ordered all the crew, twenty-nine men, into the bow; he and two other men stayed in the conning tower. As the crew squeezed forward, water filled the boat behind them, causing air pressure to build to painful levels. All this occurred in absolute darkness.
The batteries began generating chlorine gas, which rose in a greenish mist. Some gas entered the bow compartment, but the boat’s air purification system kept it from reaching deadly concentrations. The air supply dwindled.
On shore, naval officials did not learn of the crisis for two hours and then dispatched two floating cranes and a salvage ship, the Vulcan. The rescuers devised a plan to raise the bow to the surface so that the men within could climb out through the two forward torpedo tubes.
It took eleven hours for divers to place the necessary cables around the bow. The cranes began lifting the boat. The bow became visible.
The cables broke.
The boat fell backward into the sea. The divers tried again. This attempt took fourteen more hours. By then the twenty-nine crewmen had been sitting crammed into the bow in nearly airless darkness for more than twenty-seven hours. But this attempt worked. The men emerged through the tubes, tired and gasping for air, but alive.
The conning tower containing the captain and the two other men remained underwater. Five more hours passed before the Vulcan at last managed to bring the entire boat to the surface. When the rescuers opened the conning-tower hatch, they found its interior to be nearly dry, but the three men within were dead. Chlorine gas had seeped upward into the tower through speaking tubes designed to allow officers to communicate with the control room below.
A subsequent investigation found that the indicator governing the ventilation valve through which the water entered the boat had been installed incorrectly. It showed the valve was closed when in fact it was open.
This outcome, though, was still better than what befell a training U-boat that sank with all aboard and could not be raised for four months. Divers who participated in an early, failed attempt at rescue heard tapping from within. When the boat was finally raised, the cause of the disaster was obvious. It had struck a mine. As to what had occurred within, a seaman present when the hatch was forced open found vivid evidence of the kind of death submariners most feared. He wrote, “The scratches on the steel walls, the corpses’ torn finger-nails, the blood-stains on their clothes and on the walls, bore all too dreadful witness.”
THE FOG remained dense until about eleven o’clock Saturday morning, when Schwieger gauged visibility to be good enough to allow him to surface and continue under diesel power. It was always important to recharge the batteries, in case of a chance encounter with a destroyer or the sudden appearance of a choice target.
Soon after surfacing, Schwieger’s wireless man attempted to communicate with the Ancona, back at U-20’s base in Germany. There was no response. The wireless man reported, however, that he had picked up “strong enemy wireless activity” nearby, at 500 meters. Schwieger told him to stop signaling, to avoid revealing the boat’s presence.