This is the third prototype of the La-150. Armament was two 23mm Nudelman-Suranov NS-23 cannon in the lower fuselage.

History:
The Lavochkin La-150 (also known as the Izdeliye 150 - Aircraft 150) was designed by the Lavochkin design bureau (OKB) in response to a 1945 or to build a single-seat jet fighter using a single German turbojet. By this time both the Americans and British, as well as the Germans, had already flown jet fighters and the single Soviet jet engine under development (the Lyulka TR-1) was not yet ready for production. The design was completed quickly, but the construction of the five flying prototypes was protracted by the factory’s inexperience in building metal aircraft. The aircraft made its first flight in September 1946, but proved to require extensive modifications to meet the Soviet Air Forces’ requirements. These took so long to make and test that the aircraft was essentially obsolete by the time that they were completed. Even one varient with a much more powerful engine was inferior to other aircraft that the OKB had under development and all work was terminated in 1947. - Wikipedia