The Polikarpov ITP was a promising design for a cannon-armed fighter that was delayed by problems with the different engines used to power it and that never entered production.
The ITP was designed around two unproven water-cooled inline engines - the Klimov M-107 and the Mikulin AM-37. Two prototypes were built, the M-1 powered by the M-107 and the M-2 powered by the AM-37, but both engines proved to be unreliable.
The ITP was a low-wing monoplane, with a wooden monocoque fuselage and metal wings. The wing was made up of a centre section and two outer panels (the same configuration as on the Polikarpov I-16), and was fitted with flaps and automatic slats. The centre section contained honeycomb radiators, with the air intakes in the wing leading edge and the exhausts towards the back of the upper wing surface. The exhaust outlets could be used to provide some extra thrust.
The prototype M-1 was armed with one engine mounted SkK 37mm cannon and wing mounted 20mm cannon, justifying its name - Istrebitel Tyazhely Pushechny or Fighter, Heavy Gun. Later it was rearmed with a 20mm cannon in the nose. The aircraft could also carry four 100kg bombs or eight RS-82 rockets under the wings.
The M-1 prototype made its maiden flight on 23 February 1942 at Novosibirsk. The unreliable M-107 engine repeatedly disrupted the test programme, and towards the end of the year was replaced with the M-107A. The modified aircraft was then used for static tests and structural testing, so never flew again. The aircraft had an estimated top speed of 382mph or 400mph with the extra boost from the exhaust.
The M-2 prototype was built around the AM-37 engine, and was armed with three 20mm cannon. This engine was if anything less reliable than the M-107, and had to be replaced with a 1,600hp AM-39 engine before the aircraft made its maiden flight. This came on 23 November 1943, but the flight test programme didn't begin until the summer of 1944. In tests the modified M-2 prototype had a top speed of 403mph, a service ceiling of 37,700ft but a disappointing rate of climb.
The modified M-2 was on a par with the best Soviet single seat fighters, but it offered little if any advantage over the aircraft already in production, while Polikarpov's designs were no longer in favour. As a result the ITP never entered production.