S3:

Intelligence was the war fighting function with the most impact on the North Korean push to the Pusan Perimeter in the summer of 1950.  The US forces stationed in Korea were woefully ill-informed about the capabilities of their Anti-Armor weapon systems on the North Korean T-34 tanks.  This lack of effects on North Korean armored formations combined with well disciplined maneuver practices (which were also unknown to US Forces) on the part of the North Korean army contributed greatly to the rapid push south by Communist forces.  US intelligence has little knowledge of the tactics, doctrine, and TTPs of the North Korean forces.  In short the US went into the fight largely blind in the Summer of 1950 and the results were quite evident.