Did Marines, Army share lessons learned in Vietnam?

My cousin Nicky was an Army helicopter pilot who went to Vietnam in the summer of 1969 and was dead in 11 days.

He was cut down July 10 while undergoing a week of orientation with the Americal Division at Chu Lai. He and about 40 other new arrivals attended a lecture on grenade safety at LZ Bayonet, just off the base.

The instructor, an Army sergeant, used an M26 fragmentation grenade he thought he had disarmed. He threw it onto the classroom floor to see how the replacements would react, and it detonated.

One soldier, Spec. 5 Timothy T. Williams of Toledo, Ohio, died instantly and dozens were hurt.

My cousin, Warrant Officer Nicholas L. Venditti of Malvern, Pa., and Warrant Officer Wilbur J. Vachon III of Portland, Maine, died of their wounds at Chu Lai’s 312th Evacuation Hospital within the week. Both had been with the 16th Combat Aviation Group.

The Army classified their deaths as an accident.

Two years earlier, on March 28, 1967, a similar training accident involved Marines based outside Da Nang. A Marine instructor using an M16 mine he thought he had rendered inert accidentally killed 13 Marines of the 7th Engineer Battalion, 1st Marine Division.

According to an investigation report, a lesson learned from the mine explosion was that live ordnance must never be used in training.

The Americal Division, activated in Vietnam about six months after the Marine deaths, came under the authority of the 3rd Marine Amphibious Force, which was in charge of I Corps, the northernmost military zone in South Vietnam.

At the time of my cousin’s death, the 3rd MAF’s commander was Lt. Gen. Herman Nickerson Jr. He had been commander of the 1st Marine Division when the fatal mine blast happened, and he saw the investigation report.

After the grenade accident at Chu Lai, the Americal Division commander, Maj. Gen. Lloyd B. Ramsey, called Nickerson to report it.

So, there was chain-of-command contact between the Army and Marines in I Corps.

Here’s what I don’t get: The Marines had learned not to use live ordnance in classes. And yet two years after the Marine tragedy, the Army repeated the mistake, wasting the lives of my 20-year-old cousin and two other young men.

Didn’t the Army and Marines talk to each other? To what extent did the services communicate and disseminate lessons learned? Can anyone tell me about information-sharing in Vietnam?