from 50th Anniversary website:
Confinement of U.S. military personnel in the POW camps located in North Korea operated in three phases: July 1950 until the entry of the CCF into the war in November; the winter of 1950-1951 when several temporary camps were created that included the three "Valleys"; and the permanent camps. As mentioned, the NKPA had no POW system, just collection points. During the summer and fall of 1950, the NKPA moved POWs to the rear on foot, often by a death march. For example, during a 120-mile forced march during November 1950, approximately 130 of 700 POWs died. The First Offensive of the Chinese Communist Forces in late 1950 resulted in the capture of several thousand U.S. soldiers and Marines. Like the NKPA, the CCF at that time had no established POW system. As an expedient, the CCF set up a temporary camp called the "Valley" located 10 miles south of Pyoktong, North Korea, near the Yalu River. Primitive living conditions there resulted in the death of 500 to 700 of the 1,000 internees. American soldiers, most of them members of the 2d Infantry Division captured at Kunu-ri in November 1950, were kept at a place called "Death Valley," 30 miles southeast of Pukchin. Forty percent of the camp's 2,000 inmates died within three months. The other internment point known as "Peaceful Valley," located near Kanggye, that held about 300 U.S. POWs, had better living conditions than the other two "Valleys" and only a 10 percent death rate.
Overall, U.N. POWs died in large numbers during the first year of the war. Lack of food, shelter and medicine took its toll. During the first winter, some American POWs reported marching for days, sometimes in circles it seemed. Prisoners, weakened from battle, the cold and lack of food, who could not keep pace with their fellow prisoners were often left to die or executed by their captors. Prisoners carried and dragged one another through these marches. Some American POWs were young teenagers. One soldier captured during the Chosin Reservoir Campaign was 16 years old.
Through most of 1951, despite established camps, casualties continued to mount. Prisoners were fed what North Korean peasants lived on and medical supplies were unavailable to the doctors. Finally the death rate, sometimes approaching 40 percent, alarmed the Chinese. Soon food and medical supplies were provided and conditions improved for the rest of the war.
By 1951 the CCF decided that there was propaganda value in a POW system. The Chinese developed eight permanent POW camps that stretched over a 50-mile sector in North Korea along the Yalu River. Survivors of the "Valleys" were brought in, and Camp 5 at Pyoktong became the main camp and headquarters for the Chinese POW command. The CCF segregated the POWs according to rank, race and nationality and created interrogation and indoctrination programs. With their indoctrination program, the CCF tested each prisoner's faith in the democratic process, but the Chinese sought publicity more than converts to communism. Daily propaganda lectures and broadcasts that attacked capitalist society were conducted, and the CCF persuaded some POWs to sign peace petitions and make pro-communist statements. The term "brainwashing" obtained notoriety at this time and caused concern to American authorities. Brainwashing was defined as an intense and prolonged psychological process designed to erase an individual's past beliefs and to substitute new ones. Even though some American POWs collaborated with their captors, most of them did so for personal convenience. No confirmed cases of brainwashing came out of the Korean War.
Mistreatment of American POWs
The Chinese engaged in physical abuse of American POWs that included kicks and slaps, and there were some cases of physical torture. No cases of physical abuse resulting in the death of American POWs have been proved. However, some of the more than 2,600 men who were officially listed as having died in captivity might have perished from physical abuse. Forty percent of U.S. Army POWs died while confined, but the causes were generally attributed to unchecked disease, untended wounds, malnutrition and extreme cold. Many of these deaths occurred prior to creation of the permanent camps.
Some 670, or about 10 percent, of captured U.S. Army soldiers escaped during the Korean War. All of these escapes took place from front- line holding points or aid stations shortly after capture. There were about 50 documented escape attempts by Army POWs from the temporary and permanent camps, but none succeeded. The rough terrain, the problem of blending in with the local population, and the great distances to the UNC lines made escape very difficult.