That it was a "sneak" attack. Most people are not well versed in military science. Surprise/Sneak attacks are one of the basic elements of warfare. However, prior to the atomic age...total wars were the only types of wars that were fought (Limited Wars-limited to non-atomic weapons DIDN'T EXIST). And total wars were traditionally accompanied by a "Declaration of War." Not having a formal "Declaration of War" meant "dirty fighting" to the minds of US citizens, and most people in general during those times.