The Soviets' main interceptor was initially the Su-9, which was followed by the Su-15 and the MiG-25 "Foxbat". The auxiliary Tu-28, an area range interceptor, was notably the heaviest fighter aircraft ever to see service in the world. The latest and most advanced interceptor aircraft in the Soviet (now Russian) inventory is the MiG-31 "Foxhound". Improving on some of the flaws on the proceeding MiG-25, the MiG-31 has better low altitude and low speed performance, in addition to carrying an internal cannon.