The Mikoyan-Gurevich OKB had been working on a series of interceptors during the second half of the 1950s: the I-1, I-3U, I-7U, I-75, Ye-150, Ye-150A, Ye-152, Ye-152A, Ye-152P, and Ye-152M. The Ye-150 was noteworthy because it was built specifically to test the Tumansky R-15 engine, two of which would later be used for the MiG-25. This led to Ye-152, alternatively known as Ye-166, which set several world records. The Ye-152M (converted from one of the two Ye-152 aircraft) was intended to be the definite heavy interceptor design. But before it was finished, the PVO had selected the Tupolev Tu-128. As the work on the MiG-25 was well under way, the single-engine Ye-152M was abandoned.