Joe Louis, Rocky Marciano, Ray Robinson. Just about everyone that fought during the 40s and after up until 'Nam.
There is a great article on Dick Tiger in this weeks Boxing News in the UK.He was a lieutenant in the Biafran Armed Forces during the conflict in the late 60`s early 70`s
Tony Bellew was on SAS who dares wins, or whatever. I'm sure this counts, or not - as the saying goes.
Kassim Ouma. He taken when he was six years old and was forced to be a kid soldier in the National Resistance Army.