The U.S. air-force wants to prevent attacks on defense computer networks by unleashing a denial of service attack on those it perceives to attack its system.
For the unitiated, a "denial of services" attack is like ramming every M&M in a king size bag into your mouth at the same time. There is nothing wrong with M&M's per se, but all together they will clog your mouth, making it impossible to react by swallowing or chewing, and will ultimately result in choking, i.e. a system crash.
A defensive denial of service attack is doing the same thing, but only in response to an incoming attack. One problem: attackers funnel their attacks through multiple unwitting intermediaries. A defensive denial of service attack would slow down countless civilian networks on its way to the attacker -- if it ever made it. If one wants to attack from Point A to Point B, one could route an attack on the U.S. Air Force through Point B, so that both you and the entire U.S. Air Force are attacking the same spot. Make that spot outside the U.S. and you could have diplomatic fall-out.
Go back to the drawing board boys.