The VG 39 commenced its flight test program on 3 May 1940, unfortunately too late to change the flow of the events. The prototype differed from the VG 33 primarily in having a 1200hp Hispano-Suiza Type 89ter 12-cylinder liquid-cooled engine with an elongated propeller shaft, a revised wing structure which retained the profile and contours of the earlier wing, and a wing-mounted armament of six 7.5mm MAC 1934 M39 machine guns. During flight testing the prototype VG 39 attained a maximum speed of 625km/h at an altitude of 5750m.