The submarine warfare was one of the most crucial aspects of World War II, especially intense in the North Atlantic, where German submarines attacked Allied convoys crossing from North America to Europe. Under these harsh conditions, many Allied convoy ships made stops at the ports of Ponta Delgada and Horta to disembark shipwreck survivors, resupply, undergo repairs, or seek shelter from storms.

German submarines, known as U-Boats (short for Unterseeboot) followed by a number identifying each vessel, were highly effective in the Battle of the Atlantic, particularly until 1943. It is estimated that from September 1939 to May 1945, German Kriegsmarine submarines sank over two thousand Allied ships, causing thousands of deaths. However, the German fleet also suffered heavy losses, losing 785 of its 1,162 submarines during the war.

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The U-581

One of these submarines was the U-581, commissioned on July 31, 1941. After a training period, it began operational activity in December 1941 under the command of Werner Pfeifer.

On January 10, 1942, U-581 departed from its base in Saint-Nazaire on the French coast for its second mission, tasked with reinforcing the "wolfpack" tactics used to attack Allied convoys crossing the Atlantic.

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Attack Near the Azores

On January 16, north of the Azores, the Allied convoy WS15 was attacked by German submarines. The British troopship Llangibby Castle, carrying war material, was torpedoed by U-402 and suffered serious operational damage. Due to a counterattack by Allied escort ships, the German submarines lost contact with the target.

The Llangibby Castle was a very tempting target for the Germans. Although U-581 had completed its mission and was returning to base, it received orders to locate the Llangibby Castle near the Strait of Gibraltar.

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The Encounter with HMS Rosemode

On January 19, about 200 miles west of Gibraltar, U-581 encountered the British auxiliary corvette HMS Rosemode. The U-boat attacked and torpedoed the ship, triggering the explosion of its depth charges. The Rosemode sank quickly, with all 25 crew lost.

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Move to Faial Island

The next day, U-581 was instructed to proceed to Faial Island to locate the Llangibby Castle, which was undergoing repairs there.

On the night of January 31, the submarine approached Faial from the south. According to international conventions, the Llangibby Castle should have been anchored somewhere on the island, as the allowed stay in the neutral port of Horta had expired. Since the ship was not seen in any of the island's bays, U-581 concluded it was anchored inside Horta’s inner harbor.

The submarine then entered the harbor submerged and, using its periscope, Commander Werner Pfeifer spotted the Llangibby Castle anchored ahead. However, seeing vehicles and civilians moving along the Horta waterfront, Pfeifer decided not to attack, fearing civilian casualties and damage to residential buildings caused by the explosion of the ship and its ammunition. Instead, he left the harbor and took a position about 12 miles south to wait for U-402 so they could attack the Llangibby Castle together once it left Horta for Gibraltar.

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Allied Response and Final Battle

When U-402 arrived, both submarines coordinated their positions to prepare for an attack. However, British destroyers HMS Wescott, HMS Croome, and HMS Exmoor had also arrived to escort the Llangibby Castle.

In the early hours of February 1, after repairs were complete, preparations for departure began. The destroyers conducted Asdic sweeps — a sonar system used to detect submarines.

The U-581 was detected in the Faial Channel, and the destroyers headed toward it, with HMS Wescott leading and dropping depth charges on the submarine’s position.

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Damage and Sinking of U-581

U-581 submerged to 80 meters and performed evasive maneuvers, but a nearby depth charge explosion caused structural cracks that limited the submarine's capabilities. It began taking on water and became vulnerable to further attacks. The situation became critical due to flooding, lack of air, and the risk of deadly gas release from the batteries.

The battle lasted several hours. Facing this dire situation, Commander Werner Pfeifer decided to approach Pico Island and surface, allowing all crew members to abandon the submarine safely. The U-581 was then deliberately scuttled.

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Aftermath

The British destroyers rescued 41 of the 46 crew members; four had died. One German officer, Walter Sittek, managed to evade capture by swimming to the Mirateca area of Pico Island. He was rescued and treated first at Candelária and then in Horta by the doctor of the Portuguese destroyer NRP Douro.

Walter Sittek eventually returned to Germany, where he commanded other submarine units, survived the war, and years later returned to visit the Pico Island site where he had been rescued.

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Discovery of the Wreck

The wreck of U-581 was discovered on September 13, 2016, at a depth of about 870 meters south of Pico Island. The find was made by researchers from the Rebikoff-Niggeler Foundation, a non-profit marine research organization based in Horta, Faial Island.

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"The submarine warfare was a decisive front in WWII, with U-boats like the U-581 playing a critical role in the Atlantic conflict until their ultimate demise."
— Historical Analysis of Atlantic Naval Warfare

"Commander Pfeifer’s decision to avoid civilian casualties by sparing the Llangibby Castle in harbor reflects a rare instance of wartime restraint."
— Naval Command Studies

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