Roland,
A fine suggestion but how many ex-servicemen are there currently in the House of Commons? Maybe half a dozen? Previous generations served in the world wars so that most had a period of military service behind them but these days very few of the population even know someone who's served let alone been in themselves.
Encouraging ex-servicemen to stand for election would mean overcoming their feelings of revulsion at having to associate with the type of person that normally does that kind of thing.