On August 17, 1950, on a hill above Waegwan, South Korea. Forty-one U.S Army prisoners of war were gunned down by troops of the North Korean Korean People’s Army (KPA) during the Battle of Pusan Perimeter.
During the Battle of Taegu, elements of the US 2nd Battalion, 5th Cavalry Regiment, 1st Cavalry Division were surrounded by KPA troops crossing the Naktong River at Hill 303.

Most of the US troops escaped, but one platoon of mortar men misidentified KPA troops as Republic of Korea Army (ROK) reinforcements and was captured. KPA troops tried to move the American prisoners out of the battle, but were unable to do so because of a heavy U.S. counterattack.
US forces eventually routed the North Koreans. But during their retreat, a KPA officer ordered the 41 American prisoners to be shot so they would not slow them down.
Both sides confronted the massacre. US forces broadcast radio messages and dropped leaflets demanding the senior North Korean commanders be held responsible for the atrocity.
KPA commanders laid out stricter guidelines for handling enemy captives.
Source: Wikipedia