Vought XSO2U The Vought XSO2U was an American observation floatplane developed by Vought - Sikorsky for the United States Navy during the late 1930s . Intended to replace the Curtiss SOC Seagull in service as a scout aboard cruisers , it proved superior to the Curtiss SO3C in evaluation , but failed to win a production contract due to Vought ' s lack of manufacturing capacity . Design and development . In the late 1930s the United States Navy developed a set of specifications for a new scout - observation aircraft to operate from its cruiser s in the reconnaissance and gunnery spotting roles . Intended to replace the Curtiss SOC biplane , the requirements included that the aircraft should have folding wing s , have a superior range and speed to that of the SOC , and that the new type should be powered by the Ranger V - 770 inline engine . Designs were submitted in response to the Navy ' s specifications by Vought - Sikorsky and Curtiss - Wright . The Vought design , designated Model 403 by the company , was very similar to the company ' s OS2U Kingfisher , which was then under development to replace the SOC aboard U . S . Navy battleship s , but had its monoplane wing moved higher on the fuselage than that of the Kingfisher , and differed in the attachment method used by its single - float landing gear . In addition , the radial engine of the OS2U was replaced by the V - 770 in a squared - off cowling . Capable of being operated with either the float as a seaplane or with a conventional taildragger undercarriage as a landplane , the XSO2U utilised all - metal construction , with the exception of its control surfaces which were fabric - covered . The wings folded to the rear , in a manner similar to that of the TBF Avenger torpedo - bomber , for storage . The aircraft was capable of performing dive bombing , and could be fitted with a single bomb or depth charge on a hardpoint under each wing for the mission , or for anti - submarine warfare . Gun armament consisted of two M2 Browning machine gun s , one mounted in a fixed position firing forwards through the propeller using synchronizer gear , while the other was in a flexible position in the observer ' s cockpit for rear defense . Operational history . Assigned the serial number 1440 , the XSO2U - 1 flew for the first time , as a landplane , in July 1939 ; its first flight as a seaplane took place that December . Flight testing of the SO2U showed that the aircraft lacked directional stability ; the addition of a large ventral fin , connecting the rear of the float to the tail , helped to cure the problem . The aircraft also suffered from engine problems , however , that were not so easily cured ; the Ranger engine was well known for unreliability , and was particularly prone to overheating problems that were never satisfactoriarly solved . The aircraft ' s original XV - 770 - 4 engine was replaced by a XV - 770 - 6 , with a repositioned oil cooler , during flight testing ; despite this , the problems continued . Despite the engine issues , the SO2U - 1 was considered overall to be superior to the competing Curtiss XSO3C - 1 ; however , Vought ' s production capacity was already taken up by manufacture of the OS2U Kingfisher scout and F4U Corsair fighter . As a result , the XSO3C was declared the winner of the contract , and was ordered into production . Named Seagull by the U . S . Navy , and Seamew by the Royal Navy , the SO3C developed a disastrous reputation in service , and was retired before the SOC biplane which it was intended to replace . Following the end of the flyoff competition , the XSO2U - 1 was used as a general utility aircraft and hack by the Navy , before being supplied to the Ranger Engine Corporation in July 1942 for use in tests of the V - 770 engine . These tests were intended to assist in debugging the engine for the Bell XP - 77 lightweight fighter and Edo XOSE floatplane , but the V - 770 remained troublesome , and after two years of testing the XSO2U was returned to the Navy . Having no further use for the aircraft , the XSO2U - 1 was removed from the Navy ' s rolls on 6 July 1944 , being subsequently scrapped .