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[[image]][[/image]] THREE-ENGINED monoplane flying boat was 1931 Martin XP2M-1, using Wright Cyclones; speed was 140 mph, weight was 20,100 lbs. [[image]][[/image]] MARTIN P3M'S were production versions of XPY-1. The P3M-2 shown above had 525-hp P&W Hornets in place of Wasps in the -1 models. [[image]][[/image]] BUAER DESIGN for VP amphibian served as basis for experimental tandem engined Sikorsky XP2S-1 of 1932. Engines were P&W Wasps. [[image]][[/image]] LIQUID-COOLED Curtiss Conquerors of 600-hp powered four-engined Hall Aluminum XP2H-1 prototype which took off at 32,000 pounds. [[image]][[/image]] DOUGLAS P2D-1'S were twin-float torpedo or bombing planes originally designed T2D-2's. T2D-1's, P2D's served in VP squadrons. [[image]][[/image]] CONSOLIDATED P2Y-2, with 700-hp Cyclones, was typical of P2Y series which gradually replaced many of the old biplanes from 1933 on. The Fleet redeveloped the mission of patrol planes after WW I, operating them as long range scouts and bombers, and utilizing advancements in radio and other equipment to increase their effectiveness. Meanwhile, new technical advancements were also being investigated. Metal structure wings were built for testing on the HS's. A much larger flying boat based on the NC was designed. Construction of the Giant Boat was begun at the NAF while a prototype of the three power eggs (three coupled Liberties driving a single prop) was built and tested. However, the project was cancelled before completion. Improved versions of the F5L, with succeeding numbers, were also designed and tested. The F7L became the PN-7 to initiate the PN series which became the main effort in flying boat development for the remainder of the biplane period. None of the PN's went into production——from one to four of each were built——but they were used n fleet operations. New engines, first the larger liquid-cooled Wright and Packards. later the air-cooled engines, were incorporated in succeeding designs. Metal construction, including all metal hulls, replaced the wood of the earlier boats. And constant efforts were made to find the best hydrodynamic design. One area that seems to have been avoided was aerodynamic streamlining! In addition to the PN's, Boeing built the PB-1 in 1925 with tandem Packards. The last of the PN series, the -11 and -12, were ordered in 1927. They incorporated all the learning of the earlier models, plus the new aircooled engines. Increased emphasis on fleet patrol operations also resulted in production orders for Douglas PD-1's, similar to the last PN's. Over the next few years, other prototype and production biplanes were built, gradually incorporating improvements such as enclosed cabins and some streamlining into the basic biplane formula. Also in 1927, BuAer studies of a monoplane patrol plane design resulted in award of a contract to Consolidated 28 NAVAL AVIATION NEWS