A submarine was first used as an offensive weapon during the American Revolutionary War. The Turtle, a one-man submersible designed by an American inventor named David Bushnell and hand operated by a screw propeller, attempted to sink a British man-of-war in New York Harbor. The plan was to attach a charge of gunpowder to the ship's bottom with screws and explode it with a time fuse. After repeated failures to force the screws through the copper sheathing of the hull of HMS Eagle, the submarine gave up and withdrew, exploding its powder a short distance from the Eagle. Although the attack was unsuccessful, it caused the British to move their blockading ships from the harbor to the outer bay. On 17 February 1864, a Confederate craft, a hand-propelled submersible, carrying a crew of eight men, sank a Federal corvette that was blockading Charleston Harbor. The hit was accomplished by a torpedo suspended ahead of the Confederate Hunley as she rammed the Union frigate Housatonic, and is the first recorded instance of a submarine sinking a warship. The submarine first became a major component in naval warfare during World War I, when Germany demonstrated its full potentialities. Wholesale sinking of Allied shipping by the German U-boats almost swung the war in favor of the Central Powers. Then, as now, the submarine's greatest advantage was that it could operate beneath the ocean surface where detection was difficult. Sinking a submarine was comparatively easy, once it was found―but finding it before it could attack was another matter. During the closing months of World War I, the Allied Submarine Devices Investigation Committee was formed to obtain from science and technology more effective underwater detection equipment. The committee developed a reasonably accurate device for locating a submerged submarine. This device was a trainable hydrophone, which was attached to the bottom of the ASW ship, and used to detect screw noises and other sounds that came from a submarine. Although the committee disbanded after World War I, the British made improvements on the locating device during the interval between then and World War II, and named it ASDIC after the committee. American scientists further improved on the device, calling it sonar, a name derived from the underlined initials of the words sound navigation and ranging. At the end of World War II, the United States improved the snorkel (a device for bringing air to the crew and engines when operating submerged on diesels) and developed the Guppy (short for greater underwater propulsion power), a conversion of the fleet-type submarine of World War II fame. The superstructure was changed by reducing the surface area, streamlining every protruding object, and enclosing the periscope shears in a streamlined metal fairing. Performance increased greatly with improved electronic equipment, additional battery capacity, and the addition of the snorkel.