Based on (or converted from) the airframe of the Il-76M military freighter, this aerial refueling tanker aircraft entered service in 1987 to replace the elderly and incapable Myasishchev M-4 "Bison".
Fitted with three Severin/UPAZ PAE external refueling units, one under each wing (which are reportedly sometimes removed on missions involving only a single receiver aircraft) and one mounted on the port side of the rear fuselage, the Il-78 is a three (or sometimes two) point air-to-air probe and drogue tanker aircraft capable of delivering fuel at a rate of 900 to 2,200 liters/min.
Internally the Il-78 has a pair of enormous cylindrical, pallet-mounted fuel tanks in the cargo hold, together containing 35 tonnes of the aircraft's 100-tonne total transferable fuel load. The refueling process is monitored by an observer occupying the former tail gunner's position and controlled from the flight engineer's station in the cockpit. Receiver/tanker rendezvous is facilitated by a simple homing radar housed behind a broad flat aft-facing radome located forward of the standard rear loading ramp.