The whole notion of "firing the first shot" is simply absurd in the modern context, where you are not losing a couple of soldiers, but entire cities if you wait too long.
The rules of "fairness" have not been sufficiently re-written since the atomic age and require change. But ultimately, we are not bound by any rules of fairness, but only by our national security.
Our criminal law allows you to shoot first if you are in a situation where your life is perceived to be in danger. "Assault" can be as simple as threatening words, which we already have from Saddam.
You know, I recall how Reagan handled that sort of thing. His rule for hot pursuit: "All the way into the hangar."
Shortly afterward, two Navy fighters had an "incident" with some hostile aircraft. Several of the hostile planes were splashed. No U.S. Navy losses.
A fair fight means our guys come home. :)