" the same aircraft type that isn't equipped with armour, antimissile systems and early warning kit"
I think you find that this kit has been/to be fitted to the first aircraft as seen by the various bit's added to the body of the aircraft when it landed at Boscombe Down.( look at the side of the nose and at tailend of the plane.)
Besides I think it is in AirTanker interest that these plane return to base safely.
FighterControl • Home to the Military Aviation Enthusiast • View topic - 18-4-11 Boscombe Down FSTA/MRTT Arrival