design and its intended purpose (tracking and targeting high- and fast-flying US bombers and reconnaissance aircraft)—lacked look-down/shoot-down capability, which limited its effectiveness against low-flying targets. (This is one of the reasons why it was replaced with the Mikoyan-Gurevich MiG-31, whose Zaslon radar has that capability.) By the time the MiG-25 entered service in 1969, this was a serious shortcoming, as strategic bombing doctrine was shifting towards low-level penetration of enemy territory. After Belenko's defection to Japan exposed this flaw to the West, a government decree issued on 4 November 1976 called for urgent development of a more advanced radar. This resulted in the pulse-Doppler radar Sapphire-25 system fitted to the MiG-25PD variant. As an interceptor, typical armament includes four R-40 long-range air-to-air missiles, each fitted with either an infrared seeker (R-40T/TD) or a semi-active radar homing seeker (R-40R/RD) and a maximum range of against a high-flying target on a collision course. A fuel tank could be suspended under the fuselage. The aircraft could carry unguided gravity bombs to fulfill a rudimentary strike role. As the bombs would weigh no more and incur no more drag than its regular load of R-40 missiles, its performance was not impaired, leading to some impressive bombing feats; when released at an altitude of and a speed above Mach 2, a bomb would have a range of several tens of kilometres. The MiG-25 was theoretically capable of a maximum speed exceeding Mach 3 and a ceiling of . Its high speed was problematic: although sufficient thrust was available to reach Mach 3.2, a limit of Mach 2.83 had to be imposed as the engines tended to overspeed and overheat at higher air speeds, possibly damaging them beyond repair. The design cruising speed is Mach 2.35 (2,500 km/h) with partial afterburner in operation. The maximum speed of Mach 2.83 (3,000 km/h) is allowed to maintain no more than 5 minutes due to the danger of overheating of the airframe and fuel in the tanks. When the airframe temperature reaches , the warning lamp lights up, and the pilot must reduce airspeed. The use of a partial afterburner and a cruising flight altitude makes it possible to have a range only less than when flying Mach 0.9 at altitudes . The maximum altitude of flight without an afterburner in operation is . The poor fuel consumption in the subsonic regime, and hence range, is due to the