However, the aircraft's performance was slightly short of the operational requirements, and the failure to complete the Sokol-M, coupled with a need for supersonic interceptors, forced abandonment of the Yak-120M. The prototype was used as a testbed for RD-9F engines under the designation Yak-120MF. In 1955 and 1956 several Yak-25Ms were refitted as testbeds for air-to-air missile armament. A two-seat tactical reconnaissance aircraft prototype, the Yak-125, was developed in tandem with the Yak-120. In order to make room for two AKAFU automatic tilting camera mounts installed next to each other, the radar was removed and the nose extended slightly. The mounts carried AFA-33/100M, AFA-33/75M, or AFA-33/50M vertical photographic cameras. A flexible oblique camera mount with an AFA-33/75M or AFA-22/50M camera was positioned forward in order to cover the port and starboard areas. The ports were protected by hinged doors during take-off and landing; ports and cameras were controlled by the reconnaissance systems operator in the rear cockpit. The twin cannon of the Yak-120 were replaced by a single NR-23 with 80 rounds, positioned on the starboard side of the fuselage. The Yak-125's internal fuel capacity was increased to . The prototype was finished in August 1952, making its first flight on 26 August, with Volkov at its controls. It completed manufacturer flight tests in October 1953, and conducted state acceptance trials between December 1953 and February 1954. The Yak-125 outperformed the production Ilyushin Il-28R and Mikoyan-Gurevich MiG-15bisR, but the state commission recommended modifications and directed the construction of a small pre-production batch for service trials due to pilot and reconnaissance systems operator visibility limitations caused by the longer nose in the case of the former and the small ventral window for the latter. As a result of the state commission's comments, the Yak-125's forward fuselage was redesigned. The reconnaissance systems operator was moved to a compartment in the nose, in which oblique and vertical cameras were installed in front of the seat. Cameras were also located in the center fuselage, although the remainder of the aircraft was unchanged from the Yak-125. The modified aircraft was designated the Yak-25R. By a Council of Ministers directive of 10 March 1955, which was followed on the next day by an order of the Ministry of Aircraft Production, Yakovlev and Factory No. 292 in Saratov were tasked with building ten pre-production aircraft.