If you want to be even more conservative split the WIA in two..
50% can't go back into combat, but 50% can return in a week or two..

That would be
US: 7000 + 10.000
Total : 17.000

UK: 14.000 + 21.000
Total: 35.000


US: 17.000 / 200.000 = 8,5%
UK: 35.000 / 200.000 = 17,5%
Average : 26.000 / 200.000 = 13%