E-151 – variant E-150 – an experimental one with a movable rifle mount in two planes (the chief designer of the Fonakov), consisting of two TKB-495 30 mm guns and located on the structure built into the head part of the fuselage (in front of the cabin). The final draft design of the E-150, approved in 1957, was slightly modified. The first version of the armament consisted of two K-6b, K-7b or homing K-8 missiles, in the second, the TKB-495 guns in the DB-66 mobile rifle mount were replaced by the TKB-539 of the same caliber. The aircraft was planned to use an upgraded R15-300M engine and an AP-39 autopilot. A unique DB-66 system was specially developed for the aircraft. Its main element was a ring rotating around the axis of the air intake. On the ring on two movable washers mounted 30-mm guns TKB-495 (or TKB-539). The ring could rotate 360°, and the axes of the guns relative to the diameter of the ring by 30°, as a result, with a small frontal resistance, a firing cone of 60° was provided relative to the construction axis of the aircraft. The ammunition was originally located inside the ring in the sleeves, and the links were collected in the same sleeves. Due to the location shooting of the installation of the forward fuselage E-151 was longer than the E-150, but the size of the duct remained in the same dimensions as per the design process unit of ammunition with ribbons supply of ammunition was moved behind the cockpit. The internal aerodynamics of the elongated inlet channel, as confirmed by the purges, turned out to be more favorable for the operation of the turbojet engine. Therefore, this scheme was preserved on all subsequent aircraft of this family (starting with the E-152A).
After a dummy head portion of the fuselage E-151 with elements of armament in the test phase, the work of the movable gun mount it was found that at small angles of guns, the axis of rotation which is perpendicular to the axis of the support ring, there were some moments that could destabilize the flight on all three axes (depending on the position of the plane of swing of guns) and prevented a headshot. For this reason, the prototype of the E-151 interceptor, which according to the Resolution of the Council of Ministers was to become the second prototype of the E-150 aircraft, was not built. In the process of designing and building the layout, the E-151-2 variant was also considered, on which it was supposed to place movable guns and an annular support behind the pilot’s cabin closer to the center of mass of the aircraft.