As the antishipping missile transformed war at sea, the advent of the laser-guided bomb revolutionized precision land attack, for it could function with an average circular error of less than twenty feet from the aim point. With this kind of accuracy, the need to operate mass flights of aircraft against a single aim point at last disappeared; it was as revolutionary a development in military air power terms as, say, the jet engine or aerial refueling. Even more significantly, an aircraft dropping a laser-guided bomb could drop it from outside the majority of an enemy's air defenses, thus further reducing the likelihood of incurring losses to enemy defenses. The modern precision weapon era may be said to have begun in May 1972, when laser-guided-bomb-armed F-4 Phantoms perfunctorily took down the Paul Doumer and Thanh Hóa bridges in North Vietnam, as part of a larger campaign that shattered North Vietnam's invasion of South Vietnam in the spring of that year.