In the opening weeks of the Korean War, elements of the US 1st Cavalry Division's 5th Cavalry Regiment held defensive positions along the Nakdong River near Waegwan, South Korea, as part of the Pusan Perimeter defense. On August 15, 1950, KPA forces crossed the Nakdong and surrounded G Company and a supporting mortar platoon of H Company on Hill 303, a strategically important terrain feature overlooking Waegwan and key river crossings. Some US troops escaped, but the mortar platoon, misidentifying advancing KPA troops as expected South Korean reinforcements, was surrounded and surrendered without a fight under orders from its platoon leader, Lieutenant Jack Hudspeth. Estimates of the number of Americans captured range from 31 to 42; they were taken by the KPA's 4th Company, 2nd Battalion, 206th Mechanized Infantry Regiment, 105th Armored Division.
Over the following two days, the prisoners were held with limited food and water, moved between locations under KPA guard, and were unable to be evacuated across the Nakdong due to US artillery fire on crossing points. During this period, two American officers—Lieutenant Hudspeth and Lieutenant Cecil Newman—attempted to escape at night but were recaptured and executed. By August 17, additional captured Americans had been added to the group, bringing the total held in a gully on Hill 303 to 45.
On the afternoon of August 17, as UN forces launched an air strike and ground assault to retake Hill 303, a KPA officer determined the unit could not continue holding the prisoners while retreating and ordered them shot. KPA guards fired into the group of prisoners in the gully; accounts vary as to whether all or most of roughly 50 guards participated or whether a smaller group of about 14 guards under noncommissioned officers carried out the shooting. Guards returned afterward to shoot survivors of the initial gunfire. Only four or five men survived by hiding beneath the bodies of the dead. In total, 41 US prisoners were killed, including 26 from the mortar platoon. US forces retook the hill later that day and discovered the bodies, with hands still bound.
The massacre prompted UN commander General Douglas MacArthur to broadcast warnings to North Korean commanders on August 20, 1950, threatening to hold senior KPA leaders criminally accountable for war crimes. Captured KPA documents from around the same period show internal concern among North Korean commanders about troops' treatment of prisoners. The event was investigated by the US Senate in the early 1950s as part of a broader review of alleged Korean War atrocities. The site on Hill 303, near the later US Army installation Camp Carroll, has since been marked with memorials, with a larger monument installed in 2010 ahead of the massacre's 60th anniversary.