U.S. Navy efforts to develop a boat-hulled amphibian in the early 1930s yielded several unusual prototypes, but ultimately came to naught.
During the mid-1920s, the U.S. Navy initiated a cruiser construction program that resulted in the commissioning of 18 new ships by the end of 1939. Unlike older cruiser designs, the new vessels were capable of carrying seaplanes for scouting. Radio-equipped seaplanes were becoming vital to cruiser operations, enabling the ships to canvass vast areas without separating from the main body of the fleet. But experience gained from the 10 Omaha-class light cruisers, which had been retrofitted with catapults, showed that it was difficult to maintain aircraft aboard cruisers, especially in rough weather. Thus starting with the Northampton heavy cruiser class (CA-26 through -31) in 1928, two seaplane hangars were incorporated into the above-deck superstructure. Cruisers and battleships had previously used the same aircraft, Vought O2Us; now a new seaplane was needed that would fit inside the hangars.
The Naval Bureau of Aeronautics issued a new seaplane scout requirement in June 1931 (BuAer Design No. 106), calling for a twoseat, single-engine amphibian powered by a 400-hp Pratt & Whitney R-985 Wasp Junior. The idea of catapult-launched amphibians aboard ships was not new: Loening OLs had been on U.S. Navy battleships since 1926, and the Royal Navy had been operating boathulled Supermarine Seagulls from its warships even longer. A scout with amphibious capability would possess much greater shipto-shore versatility than a conventional floatplane, which had to be beached and rigged with wheels for shore operations.
Yet to serve aboard the new American cruisers, the aircraft would have to be smaller and lighter (i.e., a catapult weight of approximately 4,500 pounds) and, to fit within the hangar, fold to a width of 14½ feet. On top of that, it was expected to have a scouting radius of 300 miles or better, a top speed of 136 mph and the ability, with arresting gear, to land and take off from an aircraft carrier. A tall order.
Three companies responded with design proposals: Great Lakes Aircraft Corporation in Cleveland, Ohio; Loening Aeronautical Division of Keystone Aircraft Corporation in East River, N.Y.; and Sikorsky Division of United Aircraft Corporation in Bridgeport, Conn. Loening and Sikorsky were both pioneers in American amphibian development, having designed and produced several successful examples of the type for military and commercial applications. Great Lakes had gone as far as developing a twin-engine civil amphibian in 1929, of which three examples were ultimately built, but the company had never designed a seaplane to a naval specification. When BuAer issued detailed requirements for new aircraft, the process typically resulted in prototypes that were very similar in layout, but in this instance the three companies took noticeably different approaches to the same problem.
Great Lakes and Loening delivered their prototypes for testing and evaluation in November 1932. Both were single-engine, one bay biplanes with a Grumman-type manual gear retraction system—but beyond that, any similarity ended.
The Great Lakes entry, designated the XSG-1, featured a curious two-story layout. Its wings rested on a main pontoon that extended aft to support the tail group.A separate nacelle between the upper and lower wing housed the engine and the pilot’s cockpit. The gunner-observer’s station was located down in the pontoon, behind the wings. Acceptance trials revealed that the XSG-1 came up 12 mph short of the required airspeed, and visibility from the observer’s position was practically nonexistent. In late 1933, after 86 hours of testing, the aircraft was declared unsuitable for service and stricken from the inventory.
Loening’s XS2L-1 prototype, though more conventional in layout, was even less successful. Its general configuration shared much in common with the company’s K-84 Commuter, a six-place civil amphibian flown for the first time in 1929. But instead of resembling the K-84 in terms of its lowprofile cockpit and passenger cabin, the XS2L-1’s two-man crew accommodation was built up from flat glazed panels arranged around cabane struts that also supported the engine and wing center section. Although early testing indicated slightly better performance than the XSG-1, the general flying characteristics of Loening’s prototype were rated as unacceptable. The XS2L-1 test program was terminated in late 1933 after a total flight time of only 60 hours.
Sikorsky’s XSS-1 monoplane was definitely the most innovative of the three, featuring a streamlined, two-step hull mated to semi-cantilevered wings that gulled upward above the sea spray. The engine, enclosed by a NACA cowl, was strut-mounted in a nacelle between the V of the wings, and the observer-gunner’s position was sited well aft, to offer good downward visibility.
Since the XSG-1 and XS2L-1 had both proved to be underpowered for their weight, BuAer directed Sikorsky to substitute a 550- hp Pratt & Whitney R-1340D Wasp engine. The second prototype, the XSS-2, finally arrived at Anacostia in May 1933, but the acceptance trials were disappointing. Although 50 mph faster than its rivals, the XSS-2 failed its catapult testing and sustained damage to its hull in the process. The aircraft was returned to Sikorsky for repairs and the installation of flaps (to lower takeoff speeds). Acceptance trials never resumed, however, and the XSS-2 was canceled in late 1933, having logged just 40 hours of flying time.
In June 1933, amid serious doubts about the future of the amphibian program, BuAer had issued a completely new set of requirements for a folding-wing floatplane that could operate from the new cruisers. Development contracts were awarded to Curtiss, Douglas and Vought to deliver prototypes the following year. Trials conducted from mid-1934 to early 1935 yielded Curtiss a production contract for its XO3C-1, which began entering service with the fleet in late 1935 as the SOC-1 Seagull.
More than 500 Seagulls were ultimately built in four major variants, serving aboard Navy cruisers through the end of WWII. At practically the same time the British Admiralty ordered the Supermarine Walrus into production. A versatile boat-hulled amphibian, it served in significant numbers on Royal Navy battleships and cruisers from 1936 to 1945—providing an ironic coda to the failed U.S. efforts to develop a similar aircraft.
Originally published in the May 2011 issue of Aviation History. To subscribe, click here.