A difficult and emotive situation, whichever way it's handled.
It might be worth writing a polite letter to the editor of the newspaper, informing him of the facts in a non-emotive way. It may well be that whoever wrote the obituary genuinely thought, or believed, that the deceased aviator had performed this deed, and equally it might be that said aviator had indeed performed a similar deed on a different target which, over the years, has been confused with your father's action. On the other hand, it could be an 'embellishment' by either the aviator, or his family or friends, which, having 'grown' over the years, has finally come to rest, and possible exposure, as a falsity.
Before doing anything though, take advice as to any legal implications in the USA, which could be, and probably are, different to the UK, and also consider the implications and impact any actions might have on the surviving family and friends.