in service in the USSR", it was more stable and had better flight characteristics. Subsequently, the GKO authorised production at Factory N° 153 in place of the Yak-7A, from April 1942 and 261 machines were built until July. After 20 May, the aircraft were equipped with a tank behind the pilot's seat, but the pilots that used the Yak-7 on Stalingrad and on the Kuban removed it as it was not protected and affected the flight characteristics. Generally, the Yak-7B pleased its pilots. They reported that it was easy to fly at all altitudes, stable and easy to maintain and although it did not climb as quickly as a Messerschmitt Bf 109, it was as manoeuvrable and fast, except in the vertical plane. But defects were also noted: there was too much drag from the radiators, the canopy glass was of bad quality; the pilot was not protected enough, taking-off and landing distances were too long and, above all, it was underpowered. Yakovlev suggested to Klimov, the engine builder, some modifications that resulted in the M-105PF which was more powerful. With this modified engine, the Yak-7B top speed was of , it climbed much faster up to and it was more manoeuvrable both in the horizontal and the vertical planes. But because the rear tank was removed, its range was reduced and the center of gravity was moved too far forward, while M-105 defects (glycol and oil overheating, oil leaks etc.) persisted. Among the engine and armament options was the Yak-7-37 fitted with a MPSh-37 cannon, (MPSh - motornaya pushka Shpital'novo - engine mounted Shpital'nyy cannon), mounted between the engine cylinder blocks, firing through the propeller spinner. Operational history The Yak-7 proved to be an effective close support fighter although the first two-seaters were considered nose-heavy, consequently, the factory introduced a rear cockpit fuel tank. Pilots complained about the fuel tank's vulnerability since it was unarmored, and it was usually removed in the field. There were constant changes to the design based on combat observations including a definitive single-seat variant, the Yak-7B, which was produced in large numbers. After the war, some Yak-7V trainers were provided to the Poles and a single Yak-7V was delivered to the Hungarians for familiarization with the Yak-9 fighter. After trials in April–May 1942, a small batch of 22 Yak-7-37s was authorised, all of which were issued to the 42nd Fighter Aviation Regiment (IAP) at