Actually, alot of people don't know too much about the real KC-X plan...batch 1 is 179 tankers, then they are supposed to decide on the KC-Y, another batch of about 179 (give or take a hundred!). KC-Y could just be more KC-46's (the new official name of the KC-X Boeing 767 tanker), an improved B/C model of same tanker, or a whole new tanker completely. So, with modern equipment, 360 tankers should be able to replace 415 half century+ old ones...IMHO, the KC-Y is gonna happen alot faster than we think but it will actually be a KC-10 replacement since we are beating the snot out of those airframes and they currently have a worse dispatch rate than the -135's. They may stick with the original nomenclature and just call that the KC-Z plan and keep the KC-Y moniker for batch 2 of the -135 replacement. Clear as mud now?