One of the most instructive accidents that ever happened to an undersea boat was the loss and rescue of the German _U-3_. She sank to the bottom of Kiel Harbor on January 17, 1911. A small spherical buoy was released and rose to the surface, where it was picked up and a telephone attached to the end of the thin wire cable. “Hello!” “Hello! This is the captain of the _U-3_ speaking. We cannot rise, but we are resting easy and have air enough to last forty-eight hours.” “Good. The steam salvage-dock _Vulcan_ has been sent for and will be here before then, Herr Kapitan.” But before the _Vulcan_ arrived, it occurred to some one in authority to attempt to raise the _U-3_ with a large floating crane then available. The strong steel chain ready coiled at the lower end of the buoy-line was drawn up and made fast to the crane, which could not lift the 300-ton submarine bodily, but succeeded in hauling up its bow sufficiently for the twenty-seven petty officers and seamen on board the _U-3_ to be shot up through the torpedo tube to the surface. The captain and his two lieutenants chose to remain. Shortly afterwards the chain slipped and broke off one of the boat’s ventilators, letting water into the hull and drowning all three officers. Then the sea-going, steam salvage-dock _Vulcan_ reached the scene and brought the _U-3_ to the surface in three hours. “The _Vulcan_ is a double-hulled vessel, 230 feet in length with a lifting capacity of 500 tons. The width between the two hulls is sufficient to admit with good clearance the largest submarines. At a suitable height a shelf is formed along each wall of the interior opening, and upon this rests the removable floor of the dock. The two hulls of the ship are each built with water-tight compartments of large capacity, similar to those which are found in the side walls of the ordinary floating dock. When a sunken submarine is to be raised, the _Vulcan_ steams to the wreck and is moored securely in position above it. Spanning the well between the two hulls are two massive gantry cranes, each provided with heavy lifting tackle driven by electric motors. The first operation is to fill the compartments until the vessel has sunk to the required depth. The floor of the dock is then moved clear of the well. The lifting tackles are now lowered and made fast, either to chains which have been slung around the body of the submarine, or to two massive eyebolts which are permanently riveted into the submarine’s hull. At the order to hoist away, the submarine is lifted free from the mud and drawn up within the well, until its bottom is clear of the supporting shelves on the inner faces of the two hulls, above referred to. The dock floor is then placed in position on the shelves, the water is pumped out of the two hulls, and the _Vulcan_ rises, lifting the submarine and the dock floor clear of the water.”[18] [Illustration: Courtesy of the Scientific American. The _Vulcan_ salvaging the _U-3_.]