The MiG-21 was the first successful Soviet aircraft combining Fighter and Interceptor characteristics in a single aircraft. It was a lightweight fighter, achieving Mach 2 with a relatively low-powered After-burning Turbojet, and is thus comparable to the American Lockheed F-104 Starfighter Northrop F-5 Freedom Fighter and the French Mirage III. Its basic layout was used for numerous other Soviet designs; delta-winged aircraft included SU-9 Interceptor and the fast E-150 Prototype from MiG bureau while the mass-produced successful Front-line Fighter SU-7 and Mikoyan's I-75 Experimental Interceptor combined a similar fuselage shape with swept-back wings. However, the characteristic layout with the shock cone and front air intake did not see widespread use outside the USSR and finally proved to have limited development potential, mainly because of the very small space available for the radar. Like many aircraft designed as Interceptors, the MiG-21 had a short range. This was not helped by a design defect where the center of gravity shifted rearwards once two-thirds of the fuel had been used. This had the effect of making the plane uncontrollable, resulting in an endurance of only 45 minutes in clean condition. Additionally when more than half the fuel was used up, violent maneuvers prevented fuel from flowing into the engine, thereby causing the aircraft to shutdown midflight. The issue of the short endurance and low fuel capacity of the MiG-21F, PF, PFM, S/SM and M/MF variants—though each had a somewhat greater fuel capacity than its predecessor—led to the development of the MT and SMT variants. These had a range increase of 250 km (155 mi) compared to the MiG-21SM, but at the cost of worsening all other performance figures (such as a lower service ceiling and slower time to altitude). The delta wing, while excellent for a fast-climbing interceptor, meant any form of turning combat led to a rapid loss of speed. However, the light loading of the aircraft could mean that a Climb Rate of 235 m/s (46,250 ft/min) was possible with a combat-loaded MiG-21bis, not far short of the performance of the later F-16. Given a skilled pilot and capable missiles, it could give a good account of itself against contemporary fighters. Its G-limits were increased from +7Gs in initial variants to +8.5Gs in the latest variants. It was replaced by the newer variable-geometry MiG-23 and MiG-27 for ground support duties. However, not until the MiG-29 would the Soviet Union ultimately replace the MiG-21 as a maneuvering dog-fighter to counter new American air superiority types. The North Vietnamese Air Force received the first MiG-21's in 1965 and were used to such devastating effect during the early Rolling Thunder Bomber Raids that the US Navy and Air Force conducted Operation "Bolo" specifically to try and counter the MiG threat over North Vietnam. The issue of dealing with the MiG-21 led to development of what later became known as the "Top Gun" US Navy Fighter Weapons and "Red Flag" US Air Force Dissimilar Air Combat Schools (First started in 1969 to teach Navy and Air Force pilots how to deal specifically with the MiG threat over 'Nam) and affected all subsequent NATO aircraft designs for many years to come. Here I've depicted North Vietnamese MiG-21's intercepting a B-52 Bomber Stream during Operation "Linebacker" during the Vietnam War... A roll that the MiG-21 excelled at... MiG-21 PFM Fishbed F and extras by me with B-52's and added scene props from a variety of sources... Rendered in DS 2.3