The Tupolev bureau, knowing the complexion of the task assigned to them, estimated that it would be two decades before the program could produce a working prototype. They assumed that the first operational nuclear-assisted airplane could take to the air in the late 1970s or early 1980s. The program was design to operate in development phases. The first phase was designing and testing a small nuclear reactor, which properly began in late 1955. On March 1956, the Tupolev bureau was assigned by the Council of Ministers of the USSR the task of producing a flying test-bed plane as soon as possible. The Tupolev engineers decided to take an existing Tu-95M bomber and use it as a nuclear flying laboratory, the plane eventual designation were to be Tu-95LAL. By 1958, the ground phase of the program, the rig used to install the nuclear reactor on the aircraft, was ready for testing. Some time during the summer of 1958, the nuclear power plant was turned on and testing commenced. Immediately, the required level of reactor power was achieved, thus opening the path for the flight test phase. Between May and August 1961, the Tu-95LAL completed 34 research flights. Much of them made with the reactor shut down. The main purpose of the flight phase was examining the effectiveness of the radiation shielding which was one of the main concerns for the engineers. The massive amount of liquid sodium, beryllium oxide, cadmium, paraffin wax and steel plates; were the sole source of protection for the crew against the deadly radiation emerging from the core. The results were once again promising. Radiation levels were low on the crew cabin, paving the way for the bureau to design a new airframe. The next phase in the program was to produce a test aircraft designed from the beginning to use nuclear power as its main propulsion force. This was to be the Aircraft 119. This aircraft was based on the Tu-95 design. The major distinction was that two of its four engines, inboard, were to be the new NK14a turboprops with heat exchangers. The NK14a operates very similar to the direct cycle engines, the main difference is that the air, after passing through the compressor, does not go to the reactor, it goes directly to the heat exchange system. At the same time, the heat generated by the reactor, carried in the form of fluid; go to the heat exchange system. The combination of these two forces would enable the turbojet to produce the require amount of thrust. The other two outboard engines would remain NK12Ms. The NK Kuznetsov Design Bureau commenced work on the engines at the same time that the schematics of Aircraft 119 were drawn. As in the Tu-95LAL, the internal bomb bay would house the reactor. The connections leading from the reactor to the engines would run thru the main fuselage, up to the wings and then directly to the heat exchangers attached to the two inboard engines. Tupolev estimated that the first 119 were to be available for runway trials by late 1965. After trials, the 119 engines were to be replaced by a four NK14a engine configuration based on the Tu-114 commercial liner. However, the 119 never made it out of the drawing board. Budgetary constraints and the development of new conventional aircrafts designs were cited as the main reason for the cancellation of the program in August 1966. The cancellation of Aircraft 119 did not mean that the Soviet Union terminated its research into a nuclear powered aircraft. Several attempts were made in designing a nuclear-powered, supersonic bomber. Around the same time that Tupolev began working on the 119, there was a parallel program code named Aircraft 120. Vast amounts of research hours were invested on this project. Most of them on the design of a new turbojet engine and the layout of a new nuclear reactor system that would have been able to offer more protection to the crew and the aircraft sensitive avionics systems. Aircraft 120 was to be fitted with two turbojet engines on development by Kuznetsov. The reactor was to be installed near the rear part of the plane, as far from the cabin as possible. The crew consisted of the pilot, co-pilot, and navigator; enclosed in a heavy lead radiation shielding cabin. The 120 would have a conventional aerodynamics configuration with a high mounted 45 degrees swept wing, a swept empennage and a tricycle landing gear. Tupolev’s goal of reaching the testing phase for the 120 in the late 1970s never materialized, as with the 119, the 120 existence was only on the drawing board. Termination of the program was mainly for the same reasons as for the 119’s.