"Classified reports from Vietnam were giving the AR-15 high marks and providing a surprise. Reports from the field claimed that when a bullet fired from the AR-15 struck a man, it inflicted devastating injuries. The causes were apparently twofold. First, the metal jacket of early AR-15 bullets tended to shatter on impact, sending fragmentation slicing through victims. (In the army, this was variously seen as attractive and worrisome. In classified correspondence, some officers were thrilled by the perceived wounding characteristics, which one prominent army doctor described as "explosive effects." Others wondered whether the .223 round might be illegal under international convention.) Second, the bullets often turned sideways inside a victim, a phenomenon known as yaw. In one respect, the effects of yaw somewhat resemble what could be seen on the surface of a lake when a speedboat turned sharply. In this case, the energy delivery manifested itself as a shock wave within a human body, which could create stretching or rupturing injury to tissue not directly in a bullet's path. By turning, the bullet also crushed and cut more tissue as it passed through a victim, creating a larger wound channel."