Maritime History: U-Boats

The word "U-boat" comes from the German word "Unterseeboot," which translates to "undersea boat." Though the term has applied to many different submarines, it often evokes images of war vessels used during World War I and World War II. U-boats were used for many different tasks, including fighting, spying, commerce raiding, and enforcing blockades. The U-boat was a highly versatile ship and could be found around major port cities, cruise destinations, inland seaways, and the open sea.

Early U-Boats (1850-1914)

Germany first started testing submarines in 1851. The three-man Brandtaucher sank in the harbor of Kiel, which would become one of Germany's major cruise departure ports. It wouldn't be until 1903 that the first fully functional German submarine was created, the Forelle. This would be followed by the SM U-1, the first submarine to be commissioned by the German government; only one of these would be built before this model was quickly replaced by the SM-2 in 1908, doubling the number of torpedo tubes. Improvements continued with the SM U-19, which would be built in 1912 with a more powerful diesel engine.

The Brandtaucher: The Brandtaucher was located in 1887 and raised, and it can be seen on display today.
The Forelle: The Forelle was sold to Russia and used in the Russo-Japanese War.
The SM U-19: This U-boat changed the engine design for submarines.

World War I (1914-18)

At the start of World War I, the German navy had 48 submarines, but by the end of the war, this number would grow to 375. On Sept. 5, 1914, the HMS Pathfinder became the first ship to be sunk by a submarine using a self-propelled torpedo. It was sunk by U-21. U-17 would sink the first merchant vessel of the war on Oct. 20, 1914. German subs would sink more than 5,000 ships over the course of the war and lose 178 submarines to enemy actions. Allied forces lost more than 12,850,000 tons of goods due to the U-boat campaign. The sinking of the RMS Lusitania and the SS Sussex caused public perception of the German war effort to change, especially in America, where these ships had been seen as civilian vessels used for discount cruises and not military targets.

The Pour le Mérite: Twenty-nine U-boat commanders were given medals for their success in the U-boat campaign.
The U-Boat Campaign That Almost Broke Britain: U-boats strengthened blockades against Great Britain.
Lothar von Arnauld de la Perière The most successful U-boat commander sunk 189 merchant vessels and two gunboats. He commanded U-35 and U-139.
How U-Boats Launched the Age of Unrestricted Warfare: U-boats were as effective against enemy morale as they were at sinking ships. They caused fear because no one knew when they would strike.
The Surrender of German U-Boats: The U-boat fleet was surrendered on Oct. 24, 1918, to the Allies under the terms of the armistice.

Interwar Years (1919-39)

After the Treaty of Versailles in 1919, the German navy was limited in how many ships they could have in total, and they were not allowed to have any submarines at all. However, Germany did maintain a submarine design office in the Netherlands and a torpedo research center in Sweden. During the leadup to World War II, Germany started building ships for research purposes and in secret. By the start of the war, Germany already had 65 new U-boats.

Continued U-Boat Research: Germany still studied U-boat technology even though they were not allowed to build any new submarines after World War I.
U-2: In the 1930s, the Germans worked to rebuild their U-boat fleet.
The Anglo-German Naval Agreement: Signed in 1935, this agreement was an attempt to limit the German navy in the hopes of avoiding another conflict.

World War II (1939-45)

At the start of World War II, German U-boat attacks were very effective. Led by the workhorse Type VII and the larger Type IX U-boats, the German navy experienced great success for the first year and a half of the war. However, as the war went on, technological advancements in radar and sonar led to U-boat techniques changing. Soon, wolf packs of U-boats would work together to quickly destroy targets. During World War II 1,156 U-boats were built. They would sink more than 3,500 ships in the Atlantic, but the German navy lost 784 ships.

Admiral Karl Dönitz: The commander of the U-boat fleet targeted supply ships in an effort to cut off the Allies from weapons and other needed materials.
Torpedos of Germany: Torpedoes were the main weapon of the U-boats.
The Battle That Had to Be Won: Technological advancements helped turn the tables on U-boats and caused them to be less and less effective as the war went on.
U-Boat Casualties in World War II: By the end of the war, U-boats had lost nearly 75% of their forces.

Post-World War II and Cold War (After 1945)

After World War II, harsh sanctions were placed on Germany, and they would not have a navy again until 1955. The first U-boats in the new navy were two sunken Type XXIIIs and a Type XXI that had been raised. Later, in the 1960s, Germany would build the Type 201 and then the Type 205. They brought back the U designation but started fresh with the U-1. The U designation is still being used, with the newest ship being U-36, a Type 212 commissioned in 2016.

The Type 205: After the war, Germany would go on to create new submarines, which it would also designate as U-boats.
Submarines and the Future of Undersea Warfare: The world of naval warfare is ever-changing, and the U-boat has to constantly improve to stay relevant.

U-Boat Technological Developments

The U-boat has seen many different changes over the past 150 years. From very humble origins to becoming one of the most useful and feared ships on the ocean, these vessels have had to be adaptable. The modern U-boat uses an air-independent propulsion system that is safer than diesel, cheaper than nuclear subs, and quieter than both.

The Air-Independent Propulsion System: This style of propulsion was tested in World War II on the Type XVII but would not be perfected until years later.
Sonar Decoys: Learning new ways to trick sonar was very important to the U-boat's success.
The Type XXI Elektroboot U-Boat: The Elektroboot was the first attempt at a truly submersible U-boat.
Acoustic- and Electro-Absorbent Coatings: Using newly developed coatings, the U-boat was able to dodge sonar and radar.
Uncompleted U-Boat Projects: The XXVI: Many U-boat projects were never finished due to the end of World War II.

U-Boats, Submarines, and Naval Ships

U-Boats in the German Navy: Find out about some of the most important U-boats used by the German navy.
Wreck of U-3523 Discovered: One of the most infamous U-boats may have been sunk while attempting to smuggle Nazis to Argentina.
Lost U-Boats: Many U-boats were lost in World War II, and the losses were mapped to help show the scope of the war.
Reinhard Hardegen, the Last U-Boat Captain: The last captain of a World War II U-boat died in 2018.
Eyewitness Account of a U-Boat Attack: U-boat attacks caused fear during World War I, which is conveyed through eyewitness reports from the time.
Surviving U-Boats You Can Actually Visit: Many different U-boats are now in museums.
Secrets of Kent's German U-Boat: U-boats that were sunk during World War I are still being studied to determine information on their final voyages.
A Timeline of Submarine History: Learn about the past and present of submarines' development and use.
Germans Unleash U-Boats: The German U-boats in World War I ground shipping nearly to a halt.
Engima and the U-Boat War: Code books found on U-boats made capturing these ships very useful in World War II.
Lost U-Boats Still Out There: Some lost U-boats may never be found.
Sunken U-Boats a Significant Find for Historians: A sunken U-boat off the coast of North Carolina is a reminder of how far the German U-boats patrolled.
The I-Boat: The Japanese submarines used during World War II, I-boats never became as famous as their German counterparts, but they were still very useful ships.
A Coast Guard Ship That Trapped Nazi Subs: Heavily armed decoys helped to hunt and trap U-boats.