In 1965, the United States launched Operation Rolling Thunder, a sustained bombing campaign designed to stop the flow of men and supplies down the Ho Chi Minh Trail and break the will of the North Vietnamese. Originally scheduled to last only eight weeks, these nearly continuous air raids would continue for more than three years. But the bombings were largely ineffective and did little to stop the flow of weapons and fighters into North Vietnam. It has been estimated that, during Operation Rolling Thunder, the U.S. dropped almost a million tons of bombs on North Vietnam -- more bombs than it had dropped in all of World War II.