Free Dead Wake by Erik Larson

nicknamed the North Sea “Bright Hans,” but today the sea and sky were gray, as was the flat terrain that surrounded the harbor. Submarines stood side by side at their moorage, roped to one another, their conning towers like distant castles. The wind came onshore at 4 knots.
    U-20 moved seaward along the Ems River, in silence, and left almost no wake. Atop its conning tower stood Kptlt. Walther Schwieger, the boat’s captain, in his peaked cap and waterproof leathers. The tower was a squat chamber jutting up from the boat’s midsection that housed an array of controls and two periscopes, one his primary battle periscope, the other an auxiliary. During underwater attacks, Schwieger would station himself here within the tower’s thick carbon-steel walls and use the main periscope to direct his crew in launching torpedoes. When surfaced, the small deck on top of the tower gave him a promontory from which to scan the seascape around him but provided little shelter from the weather. The morning was cold; the scent of coffee rose through the hatch below.
    Schwieger guided the submarine along the river and on into the shallows outside the harbor. The boat moved due west and by about 9:30 A . M . passed the lighthouse and wireless station on Borkum, a small barrier island that served as an important landmark for departing and returning submarines.
    Schwieger had just turned thirty-two years old but already was considered one of the German navy’s most knowledgeable commanders, so much so that he was consulted on submarine matters by his superiors, and his boat was used to try out new submarine tactics. He was one of the few captains who had been in the submarine service before the war began. He was tall and slender, with broad shoulders. “A particularly fine-looking fellow,” one of his crew members said. His eyes were pale blue and conveyed coolness and good humor.
    Around noon, Schwieger’s boat entered the deep waters beyond Borkum, in a portion of the North Sea known variously as the German Bight or Heligoland Bight. Here the sea bottom fell away and on bright days the water turned a deep cobalt. In his War Log, kept for every patrol, Schwieger noted that the sea was running a three-foot swell from the west and that visibility was good.
    Although he was free to submerge the vessel if he wished, he kept it on the surface, where he could travel farther and faster. His twin diesel engines could generate up to 15 knots, enough to overtake most conventional merchant ships.At routine cruising speeds, say 8 knots, he could travel up to 5,200 nautical miles. Once submerged, however, Schwieger had to switch to two battery-powered engines, lest the diesels consume all the oxygen in the boat. These engines could deliver 9 knots at best, and only for a brief period. Even at half that pace, a submerged U-boat could travel only about 80 nautical miles. These speeds were so slow that sometimes U-boats trying to make their way against the fast currents of the Strait of Dover, between England and France, were unable to advance. U-boats in fact traveled underwater as little as possible, typically only in extreme weather or when attacking ships or dodging destroyers.
    For much of his first day at sea, Schwieger was able to maintainwireless contact with the station on Borkum Island and with a naval vessel in Emden Harbor, the
Ancona
, which was equipped with wireless apparatus that could communicate over long distances.Schwieger noted in his log that his ability to trade messages with the Borkum transmitter ceased when his U-boat was 45 sea miles out but that he maintained a good connection with the
Ancona
. Along the way his wireless operator repeatedly sent test signals, something U-boat wireless operators often did, as if to postpone the inevitable moment when the boat would be out of range of all friendly sources and utterly on its own.
    This isolation made the U-boat distinct among Germany’s naval forces. Surface ships usually