The I-12 had a central nacell with a pusher and a tractor engines, and very slender
twin tail booms. It was armed with two recoilless 76mm cannons, incorporated in the hollow tail booms! I-12 was
proposed and designed by Victor Nikolaevich Chernyshov, working at the
AGOS section of the TsAGI
Aircraft took of at the end of 1931, but refinements lasted until
1933. Aircraft failed to pass factory tests due to
poor flight characteristics. Tall fixed landing gear, poor aerodynamics of engine cowling, metal corrugated ('gofre')
wing skin produced huge drag. Plus a common mess of tandem engines - pusher propeller efficiency drops in air flow disturbed
by the tractor propeller.
But the worst was that there were no way for pilot to bail out. Pusher propeller had no emergency stop/drop system,
and the cockpit was not equipped with catapult.
On May 19, 1932 first attempt to fire cannons. One
APK-4 exploded, damaging tail boom. Test pilot I.F.kozlov landed
crippled aircraft safely.
Only one prototype was built. Second ANT-23bis, equipped with emergency systems was not finished.
Sources , Vol.1 p.439-440;