The so-called Mark X is not a pilot's watch. The IWC W.W.W. is one of 12
brands selected by the MoD to supply the British Army in 1945. These 12
watches are referred by collectors as the The Dirty Dozen after a 1967 film
starring Lee Marvin. The IWC W.W.W. shows up in the secondary market
occasionally with several dials: the original dial, the MoD dial, the NATO
dial, and the IWC replacement dial.
If it's a milpilot's watch you are looking for, then the Mark 11 is your goal.
The RAF, the RAAF, the RNZAF, the SAAF and the BOAC, all acquired the Mark 11
for their pilots, and navigators for celestial navigation. There are dial and
case back engravings variations in all these Mark 11. There is also the
civilian Mak 11, Ref 2612
CAVEAT EMPTOR, there are many Frankenstein IWC W.W.W. and Mark 11 out there.
Research is essential.
If you are looking for one the Marks IWC has issued since the Mark XII, then
you have plenty of choices.