Stratoforts Lambast Cong In 6 SweepsSAIGON (UPI) - U.S. B52 Stratofortresses bombed enemytargets down the length of South Vietnam last night and this morning in six raids representing some of the most concentrated attacks of the war by the giant warplanes, military spokesmen said.The B52 raids, all within 1ft hours, hit targets in some hard-to-reach Vietcong ground positions and in support of ground operations.U.S. authorities, meanwhile, revealed today that North Vietnamese shore batteries opened fire on two American destroyers and damaged one Friday as the ships sought vainly to rescue a Navy pilot whose plane was shot down during an air raid. The unidentified pilot later was rescued by a U.S. helicopter.THE DESTROYERS Stoddard and Ingersoll had to abandon the rescue attempt because the shooting was so fierce, the spokesmen said. One shell ripped a hole in the Stoddard’s starboard side just above the waterline. There was no report of U.S. casualties.In other air action. U S Air Force pilots flying out of Thai-