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Painting print of German sailors standing on the conning tower of a U-boat after torpedoing a British cargo ship.

Germany’s most successful U-Boats from WWII  

The German U-boats were so deadly and destructive during WWII that Winston Churchill famously said that they were 'the only thing that ever really frightened [him]'.


The U-boat – short for undersea boat – was one of the Third Reich’s most effective weapons during World War II. Targeting Allied warships and merchant vessels transporting food, weapons and other vital supplies, Winston Churchill famously wrote that ‘the only thing that really frightened me during the war was the U-boat peril’.

Here we’ll run through the five most successful U-boats that sailed in World War II, based on the total tonnage of ships they managed to sink.

5. U-123

Launched in 1940, U-123 was a Type IXB U-boat, a sub-type of the large IX submarines that were built specifically for long-distance excursions. She proved a formidable vessel, sinking 44 merchant ships and warships during twelve patrols, resulting in a total of 222,705 tonnages destroyed.

U-123 is perhaps most famous for her role in Operation Drumbeat. Unfolding in 1942, this was a daring Nazi offensive on Allied vessels along the North American coastline that saw thousands of merchant seamen killed. U-123 dealt the first blow of Drumbeat, sinking the British cargo ship Cyclops off the coast of Nova Scotia. The U-boat went on to destroy many more and came within sight of New York City during the operation.

Following Germany’s surrender in 1945, U-123 had a second lease of life as the French submarine Blaison. Her captain during Drumbeat, Reinhard Hardegen, became a feted figure after the war, frequently visiting the United States where he forged friendships with American war veterans. He died in 2018 at the age of 105.

4. U-124

Another Type IXB U-boat deployed during Drumbeat was U-124, which sank a total of 48 ships with a 225,637 tonnage. The U-boat was operational from 1940 to 1943 and seemed a nigh-on unstoppable force during assaults in American waters. Indeed, she managed to sink seven ships in March 1942 alone.

One target that was fatally hit by U-124 was the US merchant ship E.M. Clark, which came to a rather eerie end. Having sustained two torpedo strikes, the ship’s whistle jammed, causing it to continue to make its shrill sound as the vessel sank beneath the waves. Another ship destroyed by U-124 was the French vessel Mimosa, which was hit in June 1942 while escorting a convoy, with almost 70 men lost.

U-124 was destroyed by British forces off the coast of Portugal in April 1943. All 53 men on board perished.

3. U-103

The last IXB U-boat on this list, and the deadliest of the three, is U-103. Put out to sea in 1940, she sank 45 ships amounting to a tonnage of 237,596 during her devastating naval career. Many of her targets were destroyed off the coast of West Africa – one of these was the cargo vessel Radames, whose destruction in May 1941 was famously caught on camera.

U-103 also played a part in the attacks off the US coast and destroyed numerous merchant ships in the Caribbean. In April 1943, a British Vickers Wellington bomber attempted to destroy the U-boat with a string of depth charges, to no avail. The following month, U-103 saw off a Whitley bomber by firing at the British plane, preventing any depth charges from being released.

Having proved brilliantly hard to kill, the U-boat was decommissioned in 1944 and was scuttled the following year.

2. U-99

U-99 was a Type VIIB vessel, a sub-type of the most common, ‘workhorse’ category of U-boat. Though she was only in active service for a little less than a year, between 1940 and 1941, U-99 managed to sink 38 vessels in total, sending 244,658 tons of shipping into the ocean depths. She also had some close shaves, including an incident where she was forced to undertake a steep dive to evade a British bomber, and collided with the sea bed.

The damage was repaired, and later in that same patrol, she was able to capture the Estonian cargo ship Merisaar, with the German sailors boarding and commandeering the vessel. During a later patrol, U-99 managed to sink four British ships in three days. However, the U-boat’s luck ran out in February 1941, when she was set upon by two British destroyers in the Atlantic.

This skirmish lead to Captain Otto Kretschmer deciding to scuttle his ship and send a message to one of the British captains, imploring him to rescue his crew. Kretschmer and most of his men were indeed saved and taken in as POWs. However, three Germans went down with U-99.

1. U-48

Rounding off this list as the most famous and successful U-boat of World War II is U-48. Like U-99, this was a Type VIIB vessel, but she managed to significantly outdo her sister ship by sinking a staggering 51 targets. That amounted to a tonnage of 300,537 amassed in two years of service, making U-48 the scourge of the Atlantic Ocean.

U-48 was already out sailing by the British coast when the war began, and her first target was the British merchant ship Royal Sceptre. The U-boat’s captain, Herbert Schultze, behaved gallantly in victory, ensuring that the crew of the destroyed ship was picked up by another British vessel. However, the following year, while under the command of a different German officer, U-48 torpedoed the City of Benares, whose passengers included civilian evacuees travelling from Britain to Canada.

Dozens of women and children were killed, and there was an outcry over what the Allies called a ‘barbaric’ attack. The Germans, meanwhile, maintained it was a legitimate military target. The controversy over the City of Benares disaster has far outlived the U-boat herself. Regarded as obsolete by 1943, U-48 was eventually scuttled. Like so many other U-boats, she will rest forever on the ocean floor.