On June 14^th, 1972, more than two thousand people including teachers and students of the School of Physicians and the School of Pedagogy 7+3, teachers of the town, and labourers of Đông Sơn Village gathered together to embank the right bank of Mã River to prevent flood. Suddenly, the American aircrafts appeared and released repeated boms on the working site, which caused hundreds of casualties.

According to the statistics of the Thanh Hóa Provincial Committee of War Crimes Investigation, there were 64 dead or missing people, 100 seriously injured persons, and 187 people were under pressure of the bombing.

 Most of those who died were still very young. This event was a historical evidence that denounced the crimes of the US imperialism caused to the innocent people in Thanh Hóa.