An early Soviet monoplane with fixes landing gear and 76mm recoilless APK-4 cannon. The slogan on the side reads, “For the USSR!”
AG-1 - recoilless cannon

History:
In late 1929 Grigorovich was sent to Central Construction Bureau 7, which was really Hangar 7 at Factory 39, an OGPU secure prison for designers. Here he led the design of the Z, a secret monoplane to be armed with two 76mm APK-4 recoilless cannon designed by L. V. Kurchevsky. To speed construction the powerplant group and forward fuselage of the first prototype were the same as the Polikarpov I-5, which was also built in Hangar 7. At this time monoplanes were still structurally weak, and the wing, though of torch-welded stainless (Enerzh-6) lattice construction, still needed underwing bracing to the fixed landing gear. Apart from the semi-monocoque rear fuselage, the covering of the whole aircraft was fabric. The prototype had a Bristol Jupiter, in a helmeted cowling, while the first batch of 21 had the same 480hp engine built under license as the M-22 and cowled in a Townend ring. The second batch of 72, from Kharkov, had the 700hp M-25 (Wright Cyclone). The main landing gear variously had spatted wheels, plain wheels, or skis. The recoiled APK-4 cannons were suspended from both main spars outboard of the struts (just inboard on the first prototype), and were fed at a slow rate from a seven-round magazine in the wing. A .30 cal PV-1 machine gun was fitted to the right just ahead of the windscreen to assist aiming using the optical sight. The tailplane was mounted high to avoid the rear blast from the APK-4s.