The U-boats against which the Maritime Commission hoped Lifeboat would warn Americans were simply German submarines. The term came from the German Unterseeboot, or "undersea boat," which the Germans and later English-speaking peoples shortened to U-boat. They played a major part in both world wars and were as deadly as the film suggests.

German scientists first experimented with underwater travel in 1850, but it was not until 1903 that they built a fully functional submarine, which they promptly sold to Russia for use during the Russo-Japanese War of 1904-5. This first U-boat ran on kerosene, but before World War I, engineers had developed a diesel-fueled model. By the war's start, Germany had 29 U-boats, largely used to disrupt commercial shipping and blockade strategic ports. Armed with torpedoes, they could be deadly. In the first ten weeks of the war, U-boats took out five British ships. It was a U-boat that sank the RMS Lusitania, a non-military target, killing 1,198 people, 128 of them Americans. The event helped spur the U.S.'s entry into the war. At the war's end, the Treaty of Versailles prohibited Germany from making any more submarines, but by the start of World War II, the country had a fleet of 65, the largest in the world. They often hunted in "wolfpacks," groups of varying numbers that often ganged up to sink a single Allied ship. They patrolled throughout the Atlantic, as far South as South America and Africa and as far North as the Arctic.

The first U-boats used in World War II were primarily surface vessels capable of submerging briefly to attack. At first this was not a problem, as surface travel could not be detected by sonar. As the Allies developed more sophisticated radar systems, however, the Germans began work on a U-boat that could remain submerged for long periods of time. In 1943, they started producing the Type XXI U-boat, also known as the Elektroboote because it carried a large battery to power the ship underwater for two to three days at a time (the diesel engines required air intake). The new boats were also more streamlined to allow them to move more quickly underwater. In fact, their design would be used by the U.S. after the war as it developed new nuclear submarines.

By Frank Miller