From what I call of the original plan, the KC-X, Y, and Z. The KC-Y was supposed to be a second buy of the X to completely phase out the remaining KC-135s. And the KC-Z was supposed to be a larger KC-10 replacement.
But, we can see that ship has sailed since now the KC-46 is replacing the KC-10...so instead of using 1 KC-10 for a coronet we will need 3x -46s. Oh yea, and there will be less KC-46s at Travis and McGuire then there are KC-10's.
I'm sure this will all work out great, though.