4 0 CURRENT TOPICS. [J. 1 r. I.

Navy's Drydock Plants Grow Apace With Fleet.--The Navy Department announced recently that its construction of dry-docks, many of which are designed for building as well as repair of great capital ships, is keeping pace of the two-ocean Navy program. In fact the needs of the fleet have been anticipated in the dry dock construction program, and the docks are ready to service the grow- ing Navy as needed. This particular job is under the cognizance of the Bureau of Yards and Docks of which Rear Admiral Ben Moreel, U. S. Navy, is Chief. At Philadelphia, finishing touches are being placed on one of two giant docks, capable of docking any of the nation's battleships built or building. These like other of the major dry docks are being equipped with batteries of great cranes capable of picking up any unit of installation on a battleship. Operations adopted were designed to cut off a year and a half from the time it ordinarily takes to build such docks. Effort is now being made to cut this time even further. The major part of the great job was done under water through what is known as the "Tremie Method," whereby concrete is poured into its position, leveled by underwater drags except for refinement carried out after the job is freed of water. The hundreds of workmen involved do not see their handiwork until weeks or months after it has been done.. Divers working down under water's surface guide those above sur- face. Hydrostatic pressure--the pressure pushing up from under- neath the surface of any pumped-out area--is generally a major problem to be overcome in construction of dry-docks. It is for this reason primarily that the underwater process of laying concrete floors and submerged portions of sidewalls was developed and im- proved, for by this method the pressure from underneath is neu- tralized by the weight of the water pressing down from above. At Long Beach, California, where the Navy is building a major dry- dock the earth structure was such that the entire excavation could be carried out in "the dry" simply by sinking some 30 wells down through the foundation area and keeping pumps going. In this way hydrostatic pressure was prevented from building up. Marine railways are also a part of the drydock system. One at Key West is already being used. It will handle destroyers and other craft up to around 3,000 tons.

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