Daff,
As far as I can tell, no Rata's had cannon.
However, quite a few Ishak's did have cannon.
Fester is asking for an Ishak, not a Rata.
Polikarpov I-16 Type 24 "Ishak"
Powerplant:one Shvetsov M-62 nine-cylinder radial air-cooled engine rated at 1,000hp
Performance: maximum speed 273mph at sea level; 304mph at 10,000ft; range of 373 miles, 600 miles with external fuel tanks
Armament: four 7.62mm Shpital 'ny-komaritsky ShKAS machine-guns (two synchronised in fuselage and two unsynchronised in wings) with 650rpg, or two fuselage mounted ShKAS and two wing mounted 20mm Shpital 'ny-Vladimirov ShVAK cannon with 180rpg; a single 12.7mm Berezin UB machine-gun with 300 rounds could be added to the fuselage mounted armament and with which the wing-mounted armament was usually deleted