SIGINT Against the Chinese Intervention in the Korean War

When the North Korean People’s Army (NKPA) invaded South Korea in June 1950, the U.S. reaction was swift– air, ground, and naval forces were deployed to help repel the invaders.

Although the North Koreans conquered all of South Korea except a pocket centered on the city of Pusan, an amphibious landing at the port of Inch’on – sometimes called the greatest feat of American arms in this century–coupled with a breakout from the “Pusan Perimeter,” smashed the North Korean army. Under General Douglas MacArthur, American and South Korean forces began advancing northward toward the Yalu River, where the Korean peninsula borders China.

After the Inch’on landing, SIGINT reflected the efforts of fleeing North Korean units to regroup. The collapse of the NKPA was illustrated vividly in SIGINT, as its communications dwindled to a single active network. Many North Korean messages described defense lines, including official encouragement to “fight to the death!”