To familiarize the crews with the new aircraft, the series OS2U-2 was produced in 1940. It had non-retractable wheel landing gear. There were 158 of these logical successors to the OS2U-1, but there was virtually no difference apart from the absence of floats. Most of them were sent to the Pensacola and Jacksonville naval bases.
The OS2U-3, the last model of the Kingfisher and the one produced in the largest numbers, went into production from the summer of 1941. It differed from its predecessors mainly in having a different engine, the Pratt & Whitney R-985-AN-2 “Wasp Junior”, of the same nominal power, but enabling production to be standardized at external subcontracting firms. This enabled the Naval Aircraft Factory company to produce a further 300 aircraft under license under the designation OS2N-1, but exactly the same as the basic model. Apart from the engine, the other distinctive features of the new series included the fitting of protected tanks, a Fairchild photo-camera machine gun and armor plating for the pilot and observer’s cabin. All these innovations somewhat increased the takeoff weight and decreased the range of the aircraft.
Altogether, including the NAF OS2N-1 aircraft, 1306 examples of the OS2U-3 were produced. In spite of the large scale production for aircraft of this kind, the re-equipment of ships went quite slowly. By the end of the year, there were still cruisers equipped with the SOC-3. This was primarily because the Kingfisher was in great demand by the coastal air service. It was used in the patrol and anti-submarine roles, for rescue work, as a communications aircraft, for reconnaissance, artillery spotting and even in direct support of landing operations. Because it was so slow, the sailors jokingly expanded its designation letters OSU to “Old, Slow and Ugly”.