panel on the underside of the nose to improve his downward visibility, and he was protected by armor up to thick at the front, rear, sides and underside of his seat. The fuel capacity was in two protected tanks behind the pilot, and another four in the wings. The DIS was intended to be armed with a VYa cannon with 200 rounds in a pod beneath the nose, but the VVS preferred the Taubin MP-6 cannon. The DIS was to carry two of them with 120 rounds per gun, but they proved to be a failure and the aircraft reverted to the original VYa cannon. Each wing root was to have a synchronized Berezin UBS machine gun with 300 rounds mounted below a pair of ShKAS machine guns with 1000 rounds per gun. The gun pod could be removed and bombs up to or a torpedo could be carried instead. Flight testing The first prototype, with the internal designation of T, made its first flight on 11 June 1941. Its initial flight tests, conducted by the manufacturer between 1 July and 5 October, were a disappointment as it could reach only a speed of at , slower than estimated. The three-bladed AV-5L-114 propellers were exchanged for four-bladed AV-9B-L-149 propellers and the engine installation was redesigned, after wind tunnel tests by TsAGI (Central Aero and Hydrodynamics Institute), which revealed that the poorly designed engine accessories were the major cause of the excess drag. After modifications, the aircraft reached at an altitude of . Its time to was 5.5 minutes. Even with the improvements the LII (Lyotno-Issledovatel'skiy Institoot—Flight Research Institute) did not recommend production, but recommended that development and testing should continue. The German advance on Moscow in October 1941 forced the Institute and the DIS to evacuate to Kazan while the OKO and its factory went to Kuibyshev. The failure of the AM-37 to enter production doomed the project, albeit temporarily. The OKO, along with all other aircraft designers, had been directed to use the Shvetsov ASh-82 radial engine as a backup engine for their products in May 1941, but the evacuation disrupted the production of this version, known internally as the IT and it was not built until the autumn of 1942. Aside from the engines, it differed from the T in small respects. Its tailcone was split vertically to use as an air brake and the armament was revised