U-boat

The U-boat, or unterseeboot (undersea boat), was a German submarine used to devastating effect on Allied shipping during both World Wars. Unlike modern submarines, U-boats were only able to stay underwater for limited periods of time and had to surface to be able to attack. In World War I, German U-boat attacks were partly responsible for drawing the United States into the conflict; and in World War II, they inflicted such heavy losses on British ships that Prime Minister Winston Churchill called them his greatest wartime fear.

World War I

While the first functional submersible vehicle was built in the Netherlands in the early seventeenth century, American inventor David Bushnell was the first to develop and use a submarine as a weapon during the American Revolution. Military interest in submarines continued in the nineteenth century, and by the early twentieth century, advances in technology allowed the creation of an independently powered submersible vessel.

At the beginning of World War I, submarines were not considered effective weapons for blockading an enemy country. The vessels were so cramped they could not hold a large enough crew to successfully board and hold civilian cargo ships. The average German U-boat in World War I was 214 feet long and carried thirty-five crewmen and twelve torpedoes. In 1914, the German submarine fleet consisted of twenty mostly diesel-powered vessels.

The British kept their submarine fleet close to the coastline in a more defensive role. The Germans, who were at a decided numbers disadvantage against the British navy, sent their fleet of U-boats into the North Sea to try to even the odds by attacking British warships. After a slow start to the campaign, Germany achieved its first major success when a U-boat sank the cruiser HMS Pathfinder on September 15, 1914.

When the British successfully blockaded German ports with smaller, less vulnerable ships, Germany struck back in February 1915 by declaring unrestricted war on all ships—civilian, neutral, or military—found sailing in the war zone around Britain. Instead of capturing cargo ships transporting supplies to Britain, German U-boats would just sink them. This unprecedented change in strategy frustrated the Allies and inflicted heavy losses on their merchant fleet, sinking fifty ships from February to September 1915.

In March 1915, a U-boat sank an American cargo ship, drawing a sharp response from President Woodrow Wilson, who had pledged American neutrality in the conflict. Two months later, the British liner Lusitania was torpedoed off the coast of Ireland, killing 1,198 people, including 128 Americans. The Lusitania's sinking further angered Americans and helped shift public opinion in the United States toward war. Not wishing to draw the United States into the conflict, Germany agreed to change its policy and assure the safety of passengers on unarmed vessels.

By February 1917, however, the Germans had built a large enough fleet of U-boats they believed could overwhelm the British supply routes and starve the nation into submission. Germany again declared unrestricted war in British waters, sinking more than a thousand ships by April. The act was one of the deciding factors in pushing the United States into joining the war. With the help of U.S. warships, merchant vessels began sailing with armed escorts, a tactic that drastically cut down the number of ships lost to U-boats. By 1918, the Allies secured victory over Germany on land, and World War I was over. In the four years of the war, Germany had deployed nearly 340 U-boats, losing 178 in combat. More than five thousand Allied ships were sunk.

World War II

The treaty that ended World War I forced Germany to disarm and destroy its U-boat fleet. In 1935, under the control of Adolf Hitler, the nation announced it would rearm itself and began building a new fleet of U-boats.

By the time war started in 1939, German attempts to combat the British on the surface proved unsuccessful, so it returned to the tactics it had employed in World War I and began using U-boats to wage unrestricted war on British shipping. To counter the British use of armed convoys and avoid detection by aircraft and sonar, the commander of the German U-boat fleet, Karl Dönitz, developed the wolfpack strategy. Using this tactic, U-boats would spread out in the Atlantic until one detected an incoming convoy. Rather than attack, the vessel would radio its location to other U-boats. The wolfpack would converge on the area, wait until nightfall, and attack as a group.

This strategy—aided by the fact that the Germans had broken British naval codes—proved devastating. By December 1940, U-boats sank more than a thousand Allied ships and killed more than six thousand seamen. Aided by the United States and Canada in 1941, Britain was able to cut down on its losses; in 1942, however, the Germans had ramped up U-boat production and once again gained the advantage in the Atlantic. By mid-1942, German U-boats were inflicting heavy casualties, sinking approximately 160 ships per month. In his memoirs written years later, British Prime Minister Winston Churchill said the U-boat peril was "the only thing that ever really frightened me during the war."

The tide changed for the Allies in 1943, when technological advances in long-range radar helped Allied forces zero in on U-boats with added precision, and improved depth-charge explosives took a toll on the German fleet. The new tactics were so effective that Dönitz wondered if a traitor was giving away U-boat positions. By summer and autumn of 1943, German losses had become so great that Dönitz was forced to withdraw the fleet from the Atlantic. With the sea route to Britain wide open, the United States was able to send supplies, arms, and troops, fortifying the Allies and helping hasten Germany's defeat in 1945. By the end of the war, more than thirty thousand men had been killed in U-boat attacks and more than three thousand ships sunk. On the German side, twenty-eight thousand crew members lost their lives and 738 U-boats were destroyed.

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