g (44.1 m/s2). One MiG-25 withstood an inadvertent 11.5 g (112.8 m/s2) pull during low-altitude dogfight training, but the resulting deformation damaged the airframe beyond repair. Combat radius was , and maximum range on internal fuel (at subsonic speeds) was only at low altitude, less than . The airspeed indicator was redlined at Mach 2.8, with typical intercept speeds near Mach 2.5 in order to extend the service life of the engines. A MiG-25 was tracked flying over the Sinai Peninsula at Mach 3.2 in the early 1970s, but the flight led to the engines being damaged beyond repair. The majority of the on-board avionics were based on vacuum-tube technology, more specifically nuvistors, not solid-state electronics. Although they represented aging technology, vacuum tubes were more tolerant of temperature extremes, thereby removing the need for environmental controls in the avionics bays. With the use of vacuum tubes, the MiG-25P's original Smerch-A (Tornado, NATO reporting name "Foxfire") radar had enormous power, about 600 kilowatts. As with most Soviet aircraft, the MiG-25 was designed to be as robust as possible. The use of vacuum tubes also made the aircraft's systems resistant to an electromagnetic pulse, for example, after a nuclear blast. They were also presumably used to provide radiation hardening for the avionics. Later versions As the result of Belenko's defection and the compromise of the MiG-25P's radar and missile systems, beginning in 1976, the Soviets started to develop an advanced version, the MiG-25PD ("Foxbat-E"). Plans for a new aircraft to develop the MiG-25's potential to go faster than the in-service limit of Mach 2.8 were designed as a flying prototype. Unofficially designated MiG-25M, it had new powerful engines R15BF2-300, improved radar, and missiles. This work never resulted in a machine for series production, as the coming MiG-31 showed more promise. Operational history Soviet Union The unarmed 'B' version had greater impact than the interceptor when the USSR sent two MiG-25R and two MiG-25RB to Egypt in March 1971, which stayed until July 1972. They were operated by the Soviet 63rd Independent Air Detachment (Det 63), which was established for this mission. Det 63 flew over Israeli-held territory in Sinai on reconnaissance missions roughly 20 times. The flights were in pairs at maximum speed and high altitude, between . On 6 November 1971, a Soviet MiG-25 operating out of Egypt flying at Mach 2.5 was met by Israeli F-4Es and fired upon unsuccessfully.