The use of flaps with a boundary layer blowing system in the MiG-21PFM required the introduction of another combat trainer aircraft to facilitate mastering this system. Between 1966 and 1970, such an aircraft was produced, named MiG-21US (Type 68). It was equipped with avionics similar to the PF/PFM versions, new KM-1 ejection seats, an improved engine, and an increased fuel capacity. In NATO code, the MiG-21US was designated Mongol B.
Poland purchased 12 aircraft delivered between 1969 and 1970. The specimen with serial number 01685144, side number 4401, was built in 1969. Between 1969 and 1989, it was operated by the 11th Fighter Aviation Regiment (Wroclaw-Strachowice) and the 62nd Fighter Aviation Regiment (Poznan-Krzesiny). After decommissioning in 1990, it was transferred to the Polish Aviation Museum in Krakow.
| Wingspan | 7.15 m |
| Length | 12.18 m |
| Takeoff weight | 8000 kg |
| Maximum speed | 2175 km/h |
| Ceiling | 17700 m |
| Range | 1460 km |
| Armament | 2 R-3 guided missiles |
| Engine | R-11F2S-300 turbojet with 6175 kG thrust |
