The illustration shows a wrecking plant of the "Lake" design as it appears when operating on a sunken steamship. The case taken for illustration is that of a vessel that had been sunk for some time and where it had been considered advisable to blow away the decks in order to enable the operating compartment of the tube to be lowered right down into the cargo hold. The ship's hold is lighted up electrically, and the work of removing the material follows. A light down-haul line leads from the lower block of each set of derrick falls, and is led through a block secured conveniently to the diver's station. This line is handled by an electric winch in the operating compartment. Its purpose is to return the hoisting line with its sling to the divers after each load has been discharged upon the surface craft. As the divers operate only a few feet from the working chamber, they are protected from the surge of the surface boat, with its attendant pull on air-hose and life-line, and also from possible aggravation by currents; and, as the handling of all lines is done by mechanical power, work of recovery may be carried on in a very expeditious manner with a minimum of stress upon the operator. [Illustration: THE "CAVIAR MAP" OF SHIPPING'S GREATEST GRAVE-YARD (The little circles represent wrecks.) Reproduction of a chart published by the German Hydrographic Office, giving a list of wrecks which have occurred in the locality pictured during a period of only fifteen years. This great loss of shipping was one of the principal causes leading up to the construction of the Kiel canal.] In many waters the divers would be engaged in plain view of their tenders in the operating compartment, who would handle the down-pull lines and transmit signals by bell or telephone to the control station on the boat above. Work is thus carried on continuously by relays of divers who are thoroughly conversant with the progress of the undertaking and the circumstances affecting performance. Through the medium of the equalizing room the divers, who leave their helmets, shoes, and weights in the operating chamber, are able to undergo slowly and comfortably either decompression or compression after or before each shift. They can remain in the equalizing room as long as necessary to effect this in the way most conducive to their physical well-being. This compartment is well lighted, is fitted with seats, and provides every reasonable convenience for the diver during this intermediate stage.