Ultimately, 57 of them were court-martialed and just 23 convicted, the records show.
He served seven months of a 20-year term, the records show.
Many substantiated cases were closed with a letter of reprimand, a fine or, in more than half the cases, no action at all.
There was little interest in prosecuting Vietnam war crimes, says Steven Chucala, who in the early 1970s was legal advisor to the commanding officer of the Army's Criminal Investigation Division. He says he disagreed with the attitude but understood it.
"Everyone wanted Vietnam to go away," says Chucala, now a civilian attorney for the Army at Ft. Belvoir in Virginia.
In many cases, suspects had left the service. The Army did not attempt to pursue them, despite a written opinion in 1969 by Robert E. Jordan III, then the Army's general counsel, that ex-soldiers could be prosecuted through courts-martial, military commissions or tribunals.
"I don't remember why it didn't go anywhere," says Jordan, now a lawyer in Washington.
Top Army brass should have demanded a tougher response, says retired Lt. Gen. Robert G. Gard, who oversaw the task force as a brigadier general at the Pentagon in the early 1970s.
"We could have court-martialed them but didn't," Gard says of soldiers accused of war crimes. "The whole thing is terribly disturbing."
In March 1968, members of the 23rd Infantry Division slaughtered about 500 Vietnamese civilians in the hamlet of My Lai. Reporter Seymour Hersh exposed the massacre the following year.
By then, Gen. William C. Westmoreland, commander of U.S. forces in Vietnam at the time of My Lai, had become Army chief of staff. A task force was assembled from members of his staff to monitor war crimes allegations and serve as an early-warning system.
Over the next few years, members of the Vietnam War Crimes Working Group reviewed Army investigations and wrote reports and summaries for military brass and the White House.
The records were declassified in 1994, after 20 years as required by law, and moved to the National Archives in College Park, Md., where they went largely unnoticed.
The Times examined most of the files and obtained copies of about 3,000 pages — about a third of the total — before government officials removed them from the public shelves, saying they contained personal information that was exempt from the Freedom of Information Act.
In addition to the 320 substantiated incidents, the records contain material related to more than 500 alleged atrocities that Army investigators could not prove or that they discounted.
Johns says many war crimes did not make it into the archive. Some were prosecuted without being identified as war crimes, as required by military regulations. Others were never reported.
In a letter to Westmoreland in 1970, an anonymous sergeant described widespread, unreported killings of civilians by members of the 9th Infantry Division in the Mekong Delta — and blamed pressure from superiors to generate high body counts.