Vought’s versatile Kingfisher served as a gun spotter, patrol plane, anti-submarine scout, utility transport and trainer, but downed aircrews remembered it best as an “angel on floats”
Legendary World War I ace Eddie Rickenbacker owed his life to a Vought OS2U Kingfisher. After the B-17 in which he was flying ditched in the Pacific in 1942, Rickenbacker and other survivors spent more than three weeks in life rafts. With all hope seemingly lost, Kingfisher pilot Lieutenant William F. Ealie spotted Rickenbacker’s raft on November 12 and picked up the starving, dehydrated men. It was but one of many instances when airmen were plucked from the sea and returned to safety—sometimes after water taxiing for long distances—by Kingfishers during the war. And it was a far cry from the role originally envisioned for the rugged floatplane.
In 1919 U.S. Navy experiments had established that the accuracy of battleship gunfire beyond 10 miles increased by 200 percent if aircraft were used to pinpoint targets. By 1925 aerial gun spotting was an essential element of fleet battle doctrine, and all 18 of the Navy’s battleships had been fitted with catapults to launch float-equipped observation planes. Floatplanes also became standard equipment aboard Navy cruisers during the 1920s, used chiefly as long-range scouts rather than gun spotters.
Battleships and cruisers had originally carried the same types of two-seat floatplanes, Vought UOs and O2Us. As newer hangar-equipped heavy cruisers reached service during the early 1930s, however, the Naval Bureau of Aeronautics (BuAer) began issuing distinct requirements for two types of floatplanes: observation-scout (OS) for battleships and scout-observation (SO) for cruisers. Requirements for a new SO type circulated by BuAer in 1933 resulted in the selection of the Curtiss SOC-1 as the fleet’s standard cruiser floatplane in 1935.
With SOC-1 production underway, BuAer finally turned to the problem of finding a modern replacement for the aging fleet of Vought O3U-1s and -3s then serving aboard battleships. In addition, more floatplanes would soon be needed to equip two new battleships. The first OS requirement, announced in early 1936, called for a two-seat aircraft, convertible to either wheels or floats, with a loaded weight not exceeding 5,550 pounds, a wingspan of no more than 36 feet, a maximum range of 1,000 miles and the ability to fly off a P-6 catapult at about 60 mph. Folding wings were not specified.
BuAer awarded development contracts in May 1936 to the Chance Vought Division of United Aircraft and to the Naval Aircraft Factory (NAF), both of which were to build a single biplane prototype. Although the Navy was then in the process of acquiring monoplane torpedo- and scout-bombers to reequip carrier squadrons (Douglas TBD-1s and Vought SB2U-1s), BuAer officials remained skeptical that a monoplane could achieve the low takeoff speeds necessary for catapult operations.
Vought’s XOSU-1 prototype, an O3U-3 incorporating a flap system that allowed slightly higher takeoff weights, appeared in late 1936. Following brief trials conducted at NAS Anacostia, Md., officials determined that the XOSU-1 did not offer a sufficient improvement in performance over existing O3Us to merit further development.
The XOSN-1 was ready to fly from NAF’s Philadelphia plant in early 1937. Though it was a biplane, it was also the first floatplane to be skinned entirely in aluminum. Large automatic slats incorporated into the upper wing’s leading edges were designed to lower catapult takeoff speeds, and an I-strut system eliminated the need for interplane bracing wires. While the XOSN-1 showed a 40-percent improvement in range over the O3U-3 during early testing, its general performance was marginally less than that of an SOC-1 with the same 550-hp Pratt & Whitney R-1340 power plant.
In the spring of 1937, aiming for an OS design with better development potential, BuAer authorized construction of two more prototypes, a monoplane proposed by Vought as the XOS2U-1 and a biplane from Boeing’s Stearman Division, the XOSS-1. But this didn’t solve the immediate problem: Even if a decision between the two competing prototypes could be made by late 1938 or early 1939, production aircraft would not enter service aboard battleships until sometime in 1940. As a stopgap measure, BuAer ordered 83 SOC-3s from Curtiss in May 1937. When they were delivered in 1938 and 1939, 40 aircraft were earmarked for duty within the four battleships divisions.
The engineering team at Vought, led by designer Rex Beisel, worked nonstop on its XOS2U-1, progressing from a detailed design to a completed prototype in less than a year. Rolling out of Vought’s Stratford, Conn., plant, the XOS2U-1 made its first flight with wheels on March 1, 1938, then completed factory testing with floats by the end of May. That same month Stearman’s XOSS-1 prototype underwent initial flight-testing from the company’s plant in Wichita, Kan. Powered by an R-1340, the XOSS-1 emerged as an all-metal biplane, very similar in general layout to the XOSN-1. Required takeoff speeds were achieved via Junkers-type trailing-edge flaps that ran the full span of the upper wing.
All three of the OS prototypes arrived at NAS Anacostia during the summer of 1938 and commenced competitive trials in September. Whereas the XOSN-1 and XOSS-1 biplanes both demonstrated incremental improvements over the O3U series, the XOS2U-1 established a new state of the art in floatplane design. To save weight and simultaneously reduce fuel consumption, Beisel had decided early in the project to power his prototype with a 450-hp Pratt & Whitney R-985 Wasp Junior instead of the bigger R-1340 Wasp used by his competitors. With 30 percent less wing area, 22 percent less horsepower and 15 percent less gross weight, Beisel’s pioneering concept outperformed the competition in every flight category— speed, ceiling and range—while posting a comparable takeoff speed (55.6 mph).
The XOS2U-1’s wide operating speeds were made possible by utilizing a broadchord wing design that incorporated large full-span trailing-edge flaps for slow flight, with spoilers on the upper wing surfaces to provide roll control. It was also the first American military aircraft of any type to employ spot-welding in its primary airframe components, a structural technique that would be seen again in the design of Beisel’s V-166B project, the legendary XF4U-1 Corsair prototype. During the course of operational trials, the only changes made to the XOS2U-1 airframe were the addition of a third strut to the main float afterbody and a small step incorporated into the bottoms of the wingtip floats.
The OS competition officially ended in May 1939, when Vought was declared the winner and awarded a production contract for 54 OS2U-1s. Deliveries of all production models to the Navy were completed between May and November 1940. Departing from the tradition of naming its floatplanes Corsairs, Vought dubbed the new type Kingfisher. The OS2U-1’s first operational deployment commenced aboard USS Colorado in August 1940. Production versions, in addition to being armed—with one fixed .30-caliber machine gun synchronized to fire through the propeller, a flexible .30-caliber mounted in the rear cockpit and provision to carry two 116-pound bombs—also came with R-985-48 engines and a radio DF loop.
In December 1939, before the first OS2U-1s had been delivered, BuAer awarded Vought a second contract to manufacture 158 more aircraft as the OS2U-2, which differed from the -1 in having armor protection, self-sealing fuel tanks, an R-985-50 and fittings to carry two 325-pound depth charges. New combat requirements for virtually all American-made military aircraft, especially in terms of protection and firepower, had been prompted by intelligence reports of air combat in Europe and the Far East. U.S. naval planners were also becoming increasingly concerned about the potential threat to American shipping lanes posed by hostile submarines, with the result that 113 of the OS2U-2s delivered from November 1940 onward were completed as landplanes, to equip the newly created Inshore Patrol Squadrons on both coasts of the continental U.S. Even so, the -2 landplanes were accompanied by 70 extra sets of Edo floats, in case they were needed for shipboard duties.
In October 1940, as part of the Two-Ocean Naval Expansion Act, Vought received a contract to produce 1,006 more Kingfishers as the OS2U-3. The new version included better armor protection, increased fuel capacity and R-985-AN2 or -AN8 engines, depending on the production batch. Delivery of production OS2U-3s began in July 1941, with the final example coming off the assembly line in September 1942. All Navy battleships were reequipped with OS2Us during 1941, and by the end of the year some 446 OS2U-1s, -2s and -3s were active in Navy ship and shore squadrons, with another 90 awaiting assignment to the fleet.
Even before the U.S. entered World War II, BuAer had been facing a dilemma: Vought’s capacity to produce additional OS2U-3s for the future needs of the fleet would largely be negated by plans to place the new F4U-1 in large-scale production (585 Corsairs were initially ordered). Thus in January 1941 BuAer gave the Naval Aircraft Factory a contract to produce the OS2U-3 under license as the OS2N-1. Three hundred of these were built between April and October 1942. An improved variant of the Kingfisher, the OS2U-4, with higher-aspect-ratio wings and an R-1340 engine, was tested in 1942 but never placed in production.
During 1942 100 of the OS2U-3s built under the Navy contract were lend-leased to Great Britain and several other foreign nations. In all, 1,519 OS2U/OS2N variants had been delivered by the time production ceased in late 1942.
As a consequence of the Imperial Japanese Navy’s devastating air attack on Pearl Harbor, the battle line, centerpiece of the U.S. Navy’s tactical doctrine in the Pacific, ceased to exist as an effective fighting force. With it disappeared the OS2U’s primary role as a gunspotter. Once the Navy had regrouped to the extent of launching offensive operations against Japan, major sea engagements between ships, such as the battles of the Coral Sea and Midway, were fought principally by aircraft carriers that were out of sight of one another. In a strategic reversal, battleships functioned mainly in a support role. Ironically, when the only true action between American and Japanese battleships did take place, in the Battle of Surigao Strait in October 1944, radar-controlled gun directors largely supplanted aerial gun spotting.
Despite the demise of the battle line, the Kingfisher saw wide use in a variety of operational roles throughout WWII. During 1942 and much of 1943, Naval Aviation was chronically short of new aircraft. While OS2Us and OS2Ns were comparatively slow, they possessed excellent range and could carry up to 650 pounds of bombs or depth charges— and most important, they were available.
Inshore Patrol Squadron Kingfishers flew hundreds of hours of anti-submarine patrol sorties off American coasts. With a full load of fuel and one depth charge, OS2Us and OS2Ns could typically cover an offshore patrol radius of about 350 miles. On July 15, 1942, near Cape Hatteras, N.C.—supported by gunfire from USS Unicoi—two OS2Us attached to scouting squadron VS-9D4 depth-charged and sank the German submarine U-576. Within the same time frame, 18 OS2N-1s equipped Marine squadron VMS-3 to fly armed anti-submarine patrols close to the U.S. Virgin Islands. In the western Aleutian Islands, bomb-armed Navy Kingfishers attacked Japanese-occupied shore installations. An OS2U-3 even scored an air to-air kill in February 1945, when its pilot shot down a Mitsubishi A6M5 Zero near Iwo Jima.
In addition to serving on battleships, float-equipped OS2Us were used in scout and utility roles aboard the carriers Saratoga, Wasp and Hornet during 1942, and were attached throughout the war to all eight of the Navy’s heavy seaplane tenders and several Barnegat-class small seaplane tenders. Due to a trainer shortage, many OS2Us and OS2Ns went directly to NAS Pensacola and NAS Jacksonville, where they served as a
step-up from primary to intermediate flight training in spite of not being equipped with dual controls—testimony to the plane’s docile handling. From beginning to end, Kingfishers remained the main type of float-equipped aircraft used to transition new Navy pilots in catapult launch and recovery operations.
In mid-1942, when service trials unexpectedly revealed that the new Curtiss SO3C-1 cruiser floatplane was too underpowered for normal catapult operations, OS2Us and OS2Ns were assigned to heavy and light cruisers to make up the shortfall. And to increase the scouting radius of convoys operating without the benefit of cruiser protection, five Fletcher-class Navy destroyers commissioned in 1942 and 1943 were equipped with catapults so they could carry Kingfishers. Two of those ships, with their floatplanes aboard, subsequently deployed to the Pacific for escort duties and served until late 1943, when the scheme was deemed impractical and all five destroyers were converted back to a standard configuration. In combat operations, the presence of a large unprotected aviation fuel tank above the main deck proved to be too great a hazard.
Between 1942 and 1944, the Navy transferred 53 float-equipped OS2U-2s and -3s to the U.S. Coast Guard. During the war’s first year, Coast Guard Kingfishers augmented the Inshore Patrol Squadrons by flying armed anti-submarine patrols along the coasts, but from 1943 onward they were dedicated primarily to maritime search and rescue. Fifty-two of the lend-leased OS2U-3s joined the Royal Navy as the Kingfisher I and saw extensive wartime service as floatplane scouts, attached to catapult-equipped merchant cruisers and light cruisers. Another 18 went to the Royal Australian Air Force, where they were used for offshore patrol, plus 15 to Chile, six each to Mexico and Uruguay, and three to the Dominican Republic.
In addition to their new wartime duties, Kingfishers retained their status as the Navy’s standard battleship floatplane. The four new South Dakota–class battleships commissioned during 1942 and the four Iowa-class battleships that joined the fleet in 1943 and 1944 were equipped with Kingfishers, and they also formed the initial floatplane complement aboard the two battlecruisers commissioned in mid-1944, Alaska and Guam.
The OS2U’s gun-spotting prowess achieved renewed significance when Kingfishers were called upon to direct gunfire during the shore bombardments that preceded the amphibious assaults of the Pacific island-hopping campaign. In the midst of these operations, float-equipped Kingfishers launched from battleships also flew countless sorties to rescue downed aircrews. On April 30, 1944, while piloting an OS2U-3 from the battleship North Carolina near Truk Lagoon, Navy Lieutenant John A. Burns saved 10 airmen in one day by loading them onto the wings and taxiing over to the submarine Tang.
Late in 1944 battleships and cruisers began replacing their Kingfishers with single-seat Curtiss SC-1 Seahawks, the fleet’s new floatplane scout. But some ships carried their old OS2Us or OS2Ns right up to the war’s end. Once released from frontline duties, many Kingfishers were used as utility hacks and target tugs, and to retrieve practice torpedoes. All had been removed from active service by the end of 1946.
No examples of the OS2U or OS2N are known to be flight-worthy today, although at least eight survive on static exhibit. The OS2U-3 on display at the National Museum of Naval Aviation in Pensacola was restored after being acquired from the Uruguayan navy in 1971. An OS2U-3 salvaged from the Canadian wilderness in 1963, after being rebuilt by volunteers from Vought Aeronautics, now resides on a catapult aboard the battleship North Carolina in Wilmington. In Mobile’s Battle Memorial Park, an exMexican navy Kingfisher can be seen in the aircraft pavilion near Alabama. The National Air and Space Museum’s Udvar-Hazy Center currently displays an OS2U-3 obtained from Navy storage in 1960. Another OS2U is reportedly undergoing restoration at the Yanks Air Museum in Chino, Calif. Three facilities outside the U.S. are said to have a Kingfisher on exhibit: Whale World in Albany, West Australia; the Museo Nacional Aeronáutico y del Espacio in Santiago, Chile; and the Museo de la Revolución in Havana, Cuba.
U.S. Navy veteran E.R. Johnson is a pilot, aviation author and major in the Arkansas Wing of the Civil Air Patrol. His latest book is United States Naval Aviation, 1919-1941: Aircraft, Airships and Ships Between the Wars, which he recommends for further reading, along with William T. Larkins’ Battleship and Cruiser Aircraft of the United States Navy 1910-1949.
Click here to build your own OS2U Kingfisher.
Originally published in the November 2011 issue of Aviation History. To subscribe, click here.