The first submarines operated as little more than manned torpedoes. By the 1900s however, European and American companies developed a number of improved submarine designs, bringing war to a new frontier: the Deep. Early submarines lacked the speed needed to hunt surface vessels. However, in 1912 the Krupp firm introduced a diesel engine to its design, creating the dreaded German U-boat of WWI. From then on, submarines used diesel engines for surface faring and electric engines, ran on batteries, for undersea hunting. Subsequent designs added larger engines and many ingenious inventions, helping the submarines to operate underwater for longer periods of time, hide from sonar, and increase their lethality and survivability, but a hundred years later, the basic design and battlefield role were still the same: to silently hunt down unsuspecting and poorly armed cargo ships, or large, cumbersome and valuable targets, like aircraft carriers.