If Martians really did attack, althoug that's highly unlikely ("the chances of anything coming from mars is a million to one"), I reckon they may have thought long and hard about it before they did, and prepared for any uncertainty.
If they can travel over vast distances, it's likely that they can defeat anything the military could throw at them.....
As in the book:
"There lay the Martians-dead!-slain after all man's devices had failed, by the humblest things that God, in His wisdom, has put on this earth. Bacteria."