At least 347 and up to 504 civilians, almost all women, children, and elderly men, were murdered by U.S. Army soldiers

Some of the women were gang-raped and their bodies mutilated, and some soldiers mutilated and raped children as young as 12. The incident was the largest massacre of civilians by U.S. forces in the 20th century.

The killing began while the troops were searching the village for guerillas, and continued after they realized that no guerillas seemed to be present. Villagers were gathered together, held in the open, then murdered with automatic weapons, bayonets, and hand grenades; one large group of villagers was shot in an irrigation ditch. Soldiers also burned down homes and killed livestock.

The massacre was originally reported as a battle against Viet Cong troops, and was covered up in initial investigations by the U.S. Army.

Twenty-six soldiers were charged with criminal offenses, but only Lieutenant William Calley Jr., the leader of 1st Platoon in C Company, was convicted. He was found guilty of murdering 22 villagers and originally given a life sentence, but served three-and-a-half years under house arrest after his sentence was commuted.

https://en.wikipedia.org/wiki/My_Lai_massacre

Oh my fucking god.