Vietnam hero: Hugh Clowers Thompson Jr.

Wikipedia:

Hugh Clowers Thompson Jr. (April 15, 1943 – January 6, 2006) was a United States Army officer, serving as a warrant officer in the 123rd Aviation Battalion of the 23rd Infantry Division. 

He is credited with ending the Mỹ Lai Massacre of the South Vietnamese village known as Sơn Mỹ on March 16, 1968, alongside Glenn Andreotta and Lawrence Colburn.

During the massacre, Thompson and his Hiller OH-23 Raven crew, Andreotta and Colburn, stopped a number of killings by threatening and blocking American officers and enlisted soldiers of Company C, 1st Battalion, 20th Infantry Regiment, 11th Brigade, 23rd Infantry Division. 

Additionally, Thompson and his crew saved a number of Vietnamese civilians by personally escorting them away from advancing United States Army ground units and assuring their evacuation by air. Thompson reported the atrocities by radio several times while at Sơn Mỹ. 

Although these reports reached Task Force Barker operational headquarters, nothing was done to stop the massacre. 

After evacuating a child to a Quảng Ngãi hospital, Thompson angrily reported to his superiors at Task Force Barker headquarters that a massacre was occurring at Sơn Mỹ. 

Immediately following Thompson's report, Lieutenant Colonel Frank A. Barker ordered all ground units in Sơn Mỹ to cease search and destroy operations in the village....

See also William Calley Jr, convicted for My Lai massacre dies aged 80