The I-16 was a Soviet single-engine monoplane fighter designed in the 1930s by the Polikarpov Design Bureau. As early as 1939 few remained unconvinced that the era of the I-16 was ending. Even the installation of the more powerful M-62 and M-63 engines did not allow serial examples to exceed 500 km/h.In the summer of 1939 a prototype with upper wing surfaces covered with 2.5mm thick plywood was tested; at the same time, an I-16 Type 24 with plywood surfaces was submitted for state trials. While the plywood surface was recommended for production, it was in fact never used on serial production aircraft. Further flight testing of the I-16 in 1939 proved that subsequent modifications were not cost-effective. The I-16 was also highly sensitive to angle of attack changes of the elevator.