"It could also be used at short notice for emergencies and not affect the KC role of the other 5"
Question for you.
Why use a VIP aircraft for emergency's when we have a heap of other planes available for hire - which seems to be what the Gov't does when it needs one anyway. And Qantas (and probably others) have always come to the party and provided in times of need - Vietnam, Cyclone Tracy (with help fro the US Air Force) and others.
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