MiG-1
What an interesting aircraft!
Mikoyan-Gurevich MiG-1"The I-200 prototypes were used to evaluate a number of proposals. ... The third prototype was generally used for armament trials, experimenting with 82 mm (3.2 in)
RS-82 rockets among other weapons. For another trial it was equipped with the experimental 23 mm (0.91 in) MP-3 autocannon carried underneath the wings in external pods and redesignated as the IP-201. The 12.7 mm UBS gun was removed for the these tests and the space freed up was used to install an extra fuel tank. Initially the cannon had the low rate of fire of only 300 rounds per minute, but this was soon doubled and the gun was renamed as the MP-6. Installation of the guns was difficult, despite the aircraft's metal outer wing panels, and the wings deformed when the cannon were first mounted. It made its first, and only, flight on 1 December 1940 carrying two MP-6s and two 12.7 mm AP-12.7 machine guns, but a blocked fuel line caused a forced landing before the guns could be fired. But testing on a variety of other aircraft revealed very unsatisfactory performance by the guns and their development was canceled.
The designers were arrested on 15 May 1941 and executed on 28 October 1941."