There was a case in the UK recently where a Royal Air Force doctor refused an order to travel to Iraq, citing that the war was illegal. He was court martialled for refusing a direct order, stripped of his commission and drummed out of the forces.

During my time in the Royal Air Force, I knew that I had joined the armed forces, whose job it is to go to war when called upon. I didn't see my job as an easy way to make money or something that could be simply abandoned when war broke out.

War, legal or not, is never moral. It's ultimate aim is to kill as many of the opposing forces as possible until they surrender. Everyone joining the forces should think about whether they are willing to deal with that. If not, don't join up.