User blog comment:Ben 1,000,911/CAPTAIN AMERICA WHAT (warning: spoilers)/@comment-4548390-20160526023344/@comment-24812000-20160526041757

Interesting. That would explain a lot, and actually sounds like the answer here! Maybe even before he became Cap he gave up on Hydra, though. But yeah I agree it would have to have been in WW2 at some point.