Out of 40,000 men who served aboard German U-boats during the Second World War, more than 30,000 never returned. They sank over 2,700 Allied vessels, disrupted shipping routes, killed thousands of sailors, and turned the Atlantic into a hunting ground. This is the story behind one of the most terrifying assignments any soldier could ever be given.
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| U-Boat |
From First Dive to First Blood
Germany's journey toward undersea warfare began with a lot of trial and error. In 1850, an inventor named Wilhelm Bauer drafted plans for their first sort of submarine. It was tested, and it sank almost immediately. Somehow, Bauer and his two crew members survived, and interest in submarines continued, though slowly.
It wasn't until the early 20th century that Germany started taking the concept seriously. Unable to match Britain's battleship fleet, German strategists turned to a different kind of weapon. Instead of fighting head-on, they would target commercial shipping. If you couldn't outgun the Royal Navy, you could still starve Britain of resources.
By the time World War I erupted, Germany had 28 U-boats ready for combat. Just weeks into the war, U-9 torpedoed and sank three British cruisers in under an hour, killing more than 1,400 sailors. The rules of naval warfare had changed forever.
These early submarines weren't really submarines in the modern sense. They sailed mostly on the surface and only submerged to attack or avoid detection. Diesel engines powered them above water and charged batteries that ran electric motors underwater, but only for short periods. They had to resurface frequently, which was their most vulnerable moment.
At first, U-boats followed prize rules, stopping merchant ships and giving crews a chance to abandon ship. That fell apart once the British introduced Q-ships, merchant vessels disguised with hidden weapons. Several U-boats were destroyed this way, and commanders quickly abandoned any pretense of fairness. What followed was unrestricted submarine warfare, where any ship became a target without warning.
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| British Q-Ship |
By the end of World War I, U-boats had sunk over 5,000 ships. Nearly 5,000 German submariners were killed and 178 U-boats lost. And this was just the beginning.
The Wolfpack
After World War I, the Treaty of Versailles banned Germany from having submarines. That didn't stop them. German planners opened submarine design bureaus in neutral countries and developed boats for foreign navies. Officially, they weren't building U-boats. Unofficially, they were refining every element of the next generation.
By 1935, Hitler rejected Versailles and Germany rearmed openly. Admiral Karl Donitz pushed hardest for submarine warfare with a new strategy. Instead of sending U-boats out alone, he envisioned groups hunting together, coordinating attacks to overwhelm convoys. This became the Wolfpack.
The backbone of the fleet was the Type VII U-boat, about 220 feet long, capable of sailing nearly 9,000 nautical miles without refueling. It could dive to 750 feet in emergencies, though most operations stayed between 300 and 500 feet. Even then, hulls groaned under pressure and leaks were common.
Their mission was simple in concept. Sink every ship carrying fuel, food, weapons, or troops bound for Britain. Cut off supply lines, crush the economy, and bring the country to its knees without an invasion. On the very first day of Britain's entry into the war, U-30 fired on the SS Athenia, a civilian ocean liner. Over 100 passengers were killed. Civilians were targets too, and no one crossing the Atlantic could count on being spared.
U-boats usually carried up to 14 torpedoes, but only four to six could be loaded at a time. The G7A models were steam-powered, fast but easy to spot from the wake they left. The G7E ran on electricity, slower but silent and wake-free. Early versions were notoriously unreliable and could even circle back and hit the U-boat that fired them. Every shot had to count. When attacks succeeded, survivors often drifted for days on rafts in freezing water, hoping another convoy might spot them. |
| G7E Torpedo |
By 1941, over 6 million tons of merchant shipping had been sent to the bottom in a single year.
The Hunters Become the Hunted
The Allies fought back with an escalating series of countermeasures. Convoys were bundled into heavily guarded formations. Specialized hunter-killer groups tracked and eliminated U-boats. The main early weapon was the depth charge, a drum-shaped explosive set to detonate at a specific depth. Later came the Hedgehog, a forward-firing mortar launching two dozen charges that only exploded on contact, giving far greater precision.
Aircraft became equally deadly. Long-range patrol bombers equipped with radar, spotlights, and depth charges could catch U-boats on the surface before they had time to dive.
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| B-24 Liberator bombing the U-Boats |
By early 1943, everything caught up at once. That May became known within the German Navy as Black May. In just four weeks, 43 U-boats were sunk, a loss rate of 41%. With crews of around 50 men per boat, the human cost was staggering. The once terrifying undersea fleet was being pushed into a corner. Submarines that surfaced risked being spotted from the air. Those that stayed under faced sonar-equipped escorts and increasingly accurate attacks.
Life Inside the Boat
What made U-boat service truly brutal wasn't just the danger outside. It was what happened inside.
Patrols could last up to 12 weeks. About 50 men were packed into less than 50 cubic meters of living area. There weren't enough bunks for everyone, so crews hot-bunked in shifts. Only the captain had a private space barely larger than a closet.
Air quality deteriorated fast. Early U-boats had no effective air filtration. Within 24 hours of submersion, oxygen levels dropped and headaches became constant. Fresh food didn't last long. Within weeks, meals were reduced to dry biscuits and canned meat. Water was rationed to about two gallons per man per day for everything. Bathing didn't happen. Heat, sweat, and lack of hygiene led to skin conditions so common they had a name: U-boat rot. One common joke among Allied crews was that you could smell a U-boat before you ever saw one. |
| U-Boat Crew Member |
But what really wore men down was the constant awareness that death could come at any moment and in ways no one wanted to think about.
The Ways You Could Die
A depth charge exploding close enough could dent the hull, damage internal systems, or force the boat to the surface. At close range, it could crush a submarine completely.
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| A Crushed U-Boat |
If a U-boat descended too deep from damage or mechanical failure, the crew faced what they called a death dive. The hull would creak under pressure and the steel would begin to bend. Everyone on board knew what came next. If the ballast tanks couldn't be blown, or if the dive was already too steep, there was nothing to do but wait.
Some U-boats didn't go deep enough to implode. Instead, they hit the ocean floor in shallow water. Crews waited in the dark without power and no way out. In some cases, oxygen simply ran out. In others, cold water leaked in, rising inch by inch. That was the real fear. Not being blown apart, but being trapped alive in a steel coffin with nothing to do but wait.
Fires were another constant threat. Inside a U-boat, you were surrounded by fuel, batteries, and high-explosive torpedoes. Compartments were sealed with pressure doors to prevent flooding or flames from spreading. But those doors worked both ways. If a fire broke out in one section and the doors had to be shut, anyone left inside was trapped. If batteries were damaged, they could release toxic gases that turned lethal in minutes.
Three out of four U-boat crewmen didn't survive the war. And for most of them, the end came in one of these ways, deep beneath the surface, inside the weapon they were supposed to be operating.
40,000 men served on German U-boats. More than 30,000 never came home. They sank 2,700 ships and nearly won the Battle of the Atlantic. But the ocean didn't care which side you were on, and for three out of every four U-boat sailors, the same water they hunted in became their grave.
Written by Andreja Rakočević, a military history writer and co-creator of the RogerRoger YouTube channel.