Sorry, vasco. - the figure I had in mind was for the Victor K1 (replying to RetiredBA/BY) was 39T and the Voyager can theoretically carry 285% of this figure. I now note that the Victor K2 had a max. fuel figure of 58T, so don't doubt your figures. But is the Voyager fuel burn significantly higher than a Victor K2s? I do know that the Voyager's burn rate is considerably lower than the VC10/VC10K average burn rate, but I can't recall the exact figure I had for the Victor at present.
The rationale behind the VC10K rather than KC-10A purchase was no doubt down to cost. But when we asked why the VC10K wasn't configured as a tanker-transport, the answer was that the RAF would have had to lose some single role VC10 C Mk 1s if the VC10K had been given any official transport role.
Worthy papers were written when the VC10K Mk 4 was being converted, suggesting that it should be fitted with rather more passenger seats than planned, given that it didn't have any fuselage tanks. But They had made up Their minds and such logic was defeated.
I seem to recall that the RAF could have had 5 x 'white tail' DC-10s for the same price that was actually paid for the 3 x PanAm TriStars......??