The Submarine’s Patrol

The submarine surfaced at half past six in the evening, and Kapitänleutnant Walther Schwieger climbed through the conning tower hatch into the last light of 4 May 1915. The North Sea lay behind him. Ahead, the Atlantic opened toward the southern coast of Ireland, where his orders sent him. The war diary entry for that hour recorded the position: fifty-three degrees north, six degrees east. The diesel engines thrummed. The crew of thirty-four men went about their work in the confined space below. Schwieger had cleared the minefields and the patrols. He had brought U-20 through the most dangerous passage in the world. Now he faced a choice.

The submarine carried seven torpedoes. She had left Emden on 30 April with a full complement of weapons and fuel, but the transit through the North Sea had consumed days and reserves. The weather had been poor. Visibility had been limited. The patrol ahead would last perhaps a week, perhaps less, depending on what the sea yielded and what the British yielded. Schwieger’s orders from the Admiralty Staff in Berlin were explicit in their scope and implicit in their expectations: operate in the war zone off the southern Irish coast, attack enemy shipping, return before supplies ran low. The zone had been declared in February. The rules had been loosened in April. The passengers on the RMS Lusitania, then leaving New York, did not know that a submarine had just broken into the open sea to meet them.

Schwieger made his calculation. He ordered the helmsman to steer west-southwest, toward the shipping lanes that converged off the Old Head of Kinsale. The diesel engines pushed the submarine forward at twelve knots. The sea stretched flat and grey in every direction. The war diary noted the course and the speed. It did not note the commander’s reasoning. It never did.

U-20 was a Type U-19 class vessel, commissioned in 1913 and assigned to Schwieger in December 1914. She displaced 650 tons on the surface and 837 tons submerged. Her twin diesel engines produced 1, 700 horsepower, giving her a surface speed of fifteen knots. Her electric motors allowed her to creep beneath the waves at nine knots, though in practice she rarely exceeded five. She could dive to fifty meters, though her hull was rated for less. She carried a radio, a gyrocompass, and a periscope that could be raised to scan the horizon or lowered to hide her presence. She was a weapon, but she was also a vessel of constraints. Her range was limited. Her torpedoes were limited. Her ability to remain submerged was limited by the air her crew consumed and the batteries her motors drained. Every decision Schwieger made would be shaped by these limits.

The crew worked in a space that smelled of diesel oil, battery acid, and unwashed men. The forward torpedo room contained four tubes and the reloads that would be winched into place if the first shots failed. The central compartment held the control stations, the periscope housing, and the ladder to the conning tower. The engine room aft contained the diesels and the electric motors, along with the fuel tanks that fed them. The men slept where they could, in bunks wedged between machinery, in the passageways, on the deck plates. Hot food came from a galley no larger than a closet. Water was rationed. The air grew stale within hours of diving. The submarine was a cylinder of steel that compressed human life into its smallest possible dimensions.

Schwieger had been born in Berlin in 1885. He had joined the Imperial German Navy in 1903, served with the torpedo boat service, and transferred to the U-boat arm in 1911. He took command of U-14 in 1912 and moved to U-20 after the war began. He was thirty years old. His superiors considered him capable, though not exceptional. His war diary entries were terse and professional. They recorded positions, sightings, attacks, and results. They did not record doubt. As a submarine captain, Schwieger had been noted for his cavalier approach to attacking without being sure about the identity or nationality of his target, sometimes in breach of orders to the contrary.

The patrol had begun five days earlier, when U-20 left the anchorage at Borkum and entered the North Sea. The passage west required navigating the British minefields and the patrol lines that guarded the approaches to the German Bight. Schwieger ran on the surface at night, diving during daylight to avoid detection. The weather cooperated at first, then turned. By 2 May, the sea had grown rough. The submarine pitched and rolled in the swells, making the periscope difficult to use and the torpedoes difficult to aim. The war diary noted the conditions without complaint.

On 2 May, Schwieger sighted his first target. A Danish steamer, flying neutral colors, crossed his path. He inspected her through the periscope, noted her flag, and let her pass. The rules of engagement required identification. A neutral vessel could not be attacked without warning. A British vessel could be sunk without warning, but only if the submarine could get close enough to hit her. The Danish ship disappeared over the horizon. The war diary recorded the sighting and the decision.

The same day brought another contact. A small fishing boat, British-registered, chugged across the submarine’s course. Schwieger surfaced and ordered the crew to abandon ship. The fishermen took to their boat. The submarine’s gun crew fired rounds into the hull until the vessel sank. The war diary noted the time, the position, and the result. A small victory, and a bloodless one: the fishermen survived, and the submarine moved on.

Three hundred miles to the west, the British Admiralty was tracking U-20. The tracking came from Room 40, the cryptographic unit that had been decoding German wireless traffic since the beginning of the war. The unit’s analysts had broken the German naval codes. They read the orders sent to U-boats. They knew when the submarines left port, where they were sent, and when they were expected to return. The information was precise, but it was also incomplete. Room 40 knew the patrol zones. Exact positions remained beyond reach. The wireless intercepts gave approximate locations, but the submarines maintained radio silence while operating. The tracking was a matter of inference and estimation. As the liner steamed across the ocean, Room 40 had tracked U-20’s departure from Borkum on 30 April, her route around the north of Scotland and Ireland, and her progress along the western and southern coasts of Ireland.

On 30 April, Room 40 had recorded U-20’s departure from Borkum. The analysts knew she was heading toward the Irish coast. They knew her mission was to attack British shipping in the war zone. They passed the information to the Admiralty’s operational staff, who had to decide what to do with it. The Royal Navy could divert warships to escort merchant vessels. It could reroute shipping away from the patrol zones. It could warn captains of the specific threat. Each option carried costs. Escorts required destroyers that were needed elsewhere. Rerouting added time and fuel to already-stretched voyages. Warnings might reveal that the British were reading German codes.

The Admiralty chose limited action. General warnings went out to shipping. Specific intelligence about U-20’s position or course was withheld. The traffic that converged on Liverpool and the Bristol Channel continued on its established routes. No destroyers were assigned to escort the liners that carried passengers and munitions across the Atlantic. The reasons were strategic and practical. The Royal Navy was stretched thin. The U-boat threat was growing, but it had not yet reached the level that would justify a full reorganization of convoy routes. The passenger liners, with their speed and their prestige, were assumed to be safe. They had crossed the Atlantic for years without incident. The assumption was not tested against the new reality.

That new reality had been declared on 4 February 1915, when the German government announced that the waters around Great Britain and Ireland would henceforth be considered a war zone. Any enemy merchant vessel found in that zone would be destroyed. Neutral vessels would be at risk if they entered the zone. The declaration was a response to the British blockade of Germany, which had been in place since the war began. The British had mined the North Sea and intercepted neutral ships bound for German ports. The Germans, unable to match the British surface fleet, turned to the submarine as a weapon of economic warfare. The declaration of 4 February was the formal articulation of that strategy. It warned that Allied ships in the area would be sunk without warning beginning on 18 February.

The British government protested. The American government protested. The neutral powers protested. The Germans held firm. The war zone would take effect on 18 February. Any ship that entered after that date would do so at its own risk. The German embassy in Washington placed advertisements in American newspapers warning passengers not to travel on Allied ships. The warning appeared in the New York Times on 1 May, alongside the advertisement for the Lusitania’s departure. Readers saw the two notices side by side. They booked passage anyway.

The implementation of the war zone declaration was uneven. The German U-boat fleet was small. The submarines were mechanically unreliable. The torpedoes were prone to failure. The rules of engagement were debated within the German naval command and between the naval command and the civilian government. The admirals wanted unrestricted warfare. The politicians feared the diplomatic consequences, especially with the United States. The compromise was a policy that allowed attacks on enemy merchant vessels but required some effort to spare the lives of passengers and crew. The effort might be a warning shot. It might be allowing time to abandon ship. It might be surfacing and inspecting the target before firing. The policy was vague. The commanders in the field were left to interpret it as they saw fit.

Schwieger interpreted it according to his orders and his circumstances. He was not a pirate. He was an officer acting under the authority of his government. His mission was to sink enemy shipping. His constraints were the fuel in his tanks, the torpedoes in his tubes, and the risks he was willing to take. He did not question the policy. He executed it.

By 4 May, U-20 had reached the western edge of the North Sea. The war diary recorded the position and the time. Schwieger had brought his submarine through the most dangerous passage. The British patrols had not found him. The minefields had not caught him. The sea now opened before him. He ordered the course set for the waters off the southern tip of Ireland. The shipping lanes converged there. The liners and freighters that fed Britain’s war economy passed within sight of that coast. Schwieger would place his submarine in their path.

The submarine’s engines drove her westward. The sea remained calm. The visibility improved. The war diary noted the conditions. The crew maintained their watches. The hours passed in the routine of a vessel at sea: the change of shifts, the trimming of ballast, the checking of systems. The war, for the moment, was distant. The submarine was alone on the water, a grey shape moving beneath a grey sky.

Room 40’s analysts continued to track U-20’s progress. They read the wireless traffic that passed between the submarine and the German naval stations. The traffic was sparse. Schwieger maintained radio discipline. But the occasional transmissions allowed the analysts to estimate his position. They placed him in the eastern Atlantic, approaching the Irish coast. The estimate was accurate enough. The Admiralty knew that a U-boat was operating in the area. Exact coordinates remained unknown. Which submarine remained unconfirmed. Schwieger’s specific orders remained unread.

The distinction mattered. Room 40’s intelligence was valuable, but it was not complete. The analysts could read the codes. They could not read the minds of the German commanders. They could not predict where a submarine would choose to patrol, or what targets it would choose to attack. The intelligence was a tool. It required interpretation. The interpretation required judgment. The judgment required resources. The resources were limited.

A warning went out to shipping on 4 May. The message mentioned submarine activity off the Irish coast and advised caution, but it did not name U-20 or give specific coordinates, and no orders followed for ships to take a particular route. Captains had learned to live with warnings of this kind.

The RMS Lusitania, then three days out of New York, received the warning by wireless. Captain William Turner acknowledged the message. His course remained unchanged. His speed remained steady. The extraordinary precautions that might have been warranted by more specific intelligence were not taken. He was following his orders. He was following the standard procedures of a peacetime captain in wartime conditions. The ship steamed eastward at twenty-one knots. The passengers went about their business. The sea lay calm between the liner and the coast of Ireland.

Schwieger’s war diary for 5 May recorded another day of searching. The submarine had reached the patrol zone. The shipping lanes were within reach. The sea stretched empty in every direction. The war diary noted the visibility: good. It noted the sea state: calm. It noted the contacts: none. The submarine ran on the surface, conserving fuel, scanning the horizon through the periscope and from the conning tower. The hours passed without incident.

The monotony of the search was the reality of U-boat warfare. The submarines spent most of their time looking for targets. The targets were not always there. The Atlantic was vast. The shipping lanes were broad. A submarine could patrol for days without sighting a worthwhile target. The war diary entries for those days were brief. Position. Course. Speed. Weather. No sightings. No attacks. The war was a matter of patience.

Schwieger had patience. He had been trained to wait. The U-boat service attracted men who could endure the confinement and the boredom. The crew passed the time with cards, with books, with conversation. The food was monotonous but adequate. The air was stale but breathable. The submarine moved through the water like a predator stalking prey that might never appear.

On 5 May, the predator found nothing. The war diary recorded the negative result. The submarine continued its patrol. Schwieger adjusted his position, moving closer to the shipping lanes that approached the Irish coast. The British had established a recognition point near the Old Head of Kinsale. Ships would pass within sight of it, then turn toward their destinations. Schwieger placed his submarine in the path of that traffic.

The Admiralty’s intelligence picture remained incomplete. Room 40 knew that U-20 was operating off Ireland. The analysts estimated her position based on the last intercepted transmissions. Real-time tracking was beyond their capabilities. That Schwieger had moved closer to the coast was unknown. That he was waiting in the path of the approaching liners was unknown. The intelligence was a snapshot, not a moving picture.

The Admiralty’s operational decisions reflected the limitations of the intelligence. The warnings to shipping were general. The naval patrols were sporadic. The destroyers that might have escorted the Lusitania were occupied elsewhere. The Admiralty had decided, months earlier, that the passenger liners did not require escorts. Their speed was considered sufficient protection. Their prestige was considered a deterrent. The assumption had not been revisited.

The war diary for 6 May recorded a contact. At half past six in the morning, the lookouts sighted a steamer to the north. Schwieger submerged and approached. The target was a small vessel, British-registered, flying no flags. Schwieger fired a torpedo. The torpedo missed. The steamer changed course and disappeared into the morning haze. The war diary noted the attack and the result: no hit.

The failure was not unusual. The torpedoes of the era were unreliable. They ran deeper or shallower than set. They failed to detonate on impact. They missed their targets entirely. The commanders fired from close range, but even close range was no guarantee of a hit. The war diaries of the U-boat fleet were filled with accounts of missed shots and escaped targets.

Schwieger’s second contact came later that morning. A schooner, sailing under British colors, crossed his path. He surfaced and ordered the crew to abandon ship. The crew took to their boat. The submarine’s gun crew fired into the hull until the schooner sank. The war diary noted the time, the position, and the result — his second vessel of the patrol, after the fishing boat on 2 May. The score was small; the patrol was halfway done.

The fuel gauge fell. The torpedo count fell. The submarine had been at sea for six days. The transit to the patrol zone had consumed fuel. The return transit would consume more. The patrol could continue for perhaps four more days. Schwieger calculated his reserves. Five torpedoes remained. Enough fuel to reach home remained if he turned back soon. He chose to continue. The shipping lanes were ahead. The targets would come.

Room 40’s records for 6 May show continued tracking of U-20. Analysts estimated her position from wireless traffic and placed her off the southern coast of Ireland — correctly, as it happened. Another warning went out to shipping that day, mentioning submarine activity in slightly more specific terms than before; still U-20 was not named, and still no ship was ordered to change course.

The RMS Lusitania, now four days out of New York, received the warning. Captain Turner acknowledged the message. The ship continued on its course. The passengers continued their routines. The liner steamed eastward at twenty-one knots, carrying nearly two thousand souls and tons of munitions across waters that had been declared a war zone.

The two vessels were converging. The liner approached from the west. The submarine waited to the east. The distance between them shrank with each passing hour. The sea lay between them, calm and grey, empty of all other traffic. The war zone was a line on a map. The map was silent. The intelligence that might have made it speak was locked in the files of Room 40, unseen by the captain who needed it most.

Schwieger’s war diary for 6 May ended with a note on the weather. The sea was calm. The visibility was good. The wind was light from the southwest. The conditions were favorable for a surfaced approach. The conditions were also favorable for a submerged attack. The submarine could run on the surface, using its diesel engines and its higher speed, then dive to fire. The tactic was standard. The question was whether the targets would appear.

The night of 6 May passed without contact. The submarine ran on the surface, the diesels thrumming, the lookouts scanning the darkness for lights. The liners that crossed the Atlantic at night showed navigation lights. They were supposed to. The wartime regulations had ordered ships to darken their lights, but the regulations were inconsistently followed. Some captains doused their lights. Others kept them burning, trusting that speed and visibility would protect them. The Lusitania’s lights were burning. Schwieger did not see them. They were too far to the west.

The morning of 7 May began like the mornings before. The submarine surfaced at dawn. The lookouts climbed to the conning tower. The sea stretched flat and grey under a clear sky. The visibility was excellent. The war diary noted the conditions. The position was now approximately twelve miles south of the Old Head of Kinsale. The shipping lane was within reach. Schwieger ordered the submarine to run on the surface, conserving fuel, waiting for the traffic that must come.

The traffic came. At half past eleven, the lookouts sighted smoke on the horizon. A vessel was approaching from the west. Schwieger submerged and began his approach. The target was a steamer, British-registered, moderate size. He maneuvered into position. He raised the periscope. He sighted the target. He fired. The torpedo ran true. It struck the vessel amidships. The explosion was visible from the submarine. The vessel began to sink. The war diary noted the time: 11:30. The result: hit. The vessel was the Candidate, a British freighter. She went down within an hour.

The first success of the patrol was recorded without emotion. The war diary entry was factual. Position. Time. Target. Result. The crew of the Candidate was picked up by a passing vessel. Schwieger did not linger. He moved away from the area, reloaded his torpedo tubes, and resumed his patrol.

The second success came in the early afternoon. At half past one, the lookouts sighted another steamer. Schwieger submerged and approached. The target was larger than the first. He fired. The torpedo missed. He fired again. The second torpedo hit. The vessel was the Centurion, another British freighter. She did not sink immediately. She was damaged and drifting. Schwieger recorded the result and moved on.

The patrol was now a success. Two vessels sunk, one damaged. The torpedo count was lower. The fuel gauge was lower. The time remaining was measured in hours. Schwieger had orders to return before his supplies ran out. He could turn back now, with his victories, and be safe. Or he could remain, and wait for the traffic that continued to pass.

He chose to remain.

The decision was not recorded in the war diary. The diary recorded positions and actions. It did not record the reasoning behind them. But the reasoning can be inferred. Schwieger was a commander on patrol. His mission was to attack enemy shipping. The shipping lane was producing targets. The conditions were favorable. The risk was acceptable. He remained.

The afternoon wore on. The submarine ran on the surface, moving slowly, conserving fuel. The lookouts scanned the horizon. The sea was calm. The sky was clear. The visibility extended for miles. The war diary noted the position: approximately eleven miles off the Old Head of Kinsale. The time was approaching two o’clock.

The RMS Lusitania was approaching from the west, approximately forty miles away, steaming at twenty-one knots. She would reach the Old Head of Kinsale within two hours. The submarine was between her and her destination. The two vessels were on converging courses. The distance was closing.

Room 40’s intelligence picture for 7 May showed continued tracking of U-20. The analysts knew the submarine was operating off Ireland. They knew she had been at sea for a week. They estimated that she would return soon. Her exact position remained unknown. That she had just sunk two vessels remained unknown. That she remained on station remained unknown.

No new warnings went out that morning. The warnings that had been issued were general. They had been received by the Lusitania. They had been acknowledged. They had not changed the ship’s course or speed.

The silent map was taking shape. On one side, the German naval command, which had sent U-20 to patrol the shipping lanes. On the other side, the British Admiralty, which knew the submarine was there but chose not to share that knowledge in full. In the middle, the captain of the RMS Lusitania, who steamed toward a danger he could not see.

Schwieger’s war diary for 7 May would record what happened next. The entry would be terse. The position would be precise. The time would be noted. The result would be entered in the log. The consequences would unfold far beyond the diary’s pages.

The submarine waited. The sea was calm. The visibility was good. The afternoon sun cast long shadows on the water. The lookouts scanned the horizon. The diesels thrummed. The crew went about their work. The war diary lay open on the captain’s table, waiting for its next entry.

The Old Head of Kinsale rose in the distance, a dark line against the sky. The shipping lane passed within sight of it. The liners and freighters that fed Britain’s war economy rounded that headland and turned toward Liverpool. The RMS Lusitania would round it within hours. The submarine was positioned to intercept her. The intelligence that might have warned the liner was locked in the files of Room 40, three hundred miles away. The captain who needed it most did not know it existed.

The afternoon sun climbed higher. The sea remained calm. The submarine ran on the surface, a grey shape on a grey sea. The lookouts scanned the horizon. The hours passed. The distance shrank. The war diary waited for its next entry.