North Korean troops had the advantage of planning the invasion in advance and organizing a pre-set logistics network, but they were not able to keep this logistics network running efficiently. Their largest disadvantage was the successful large-scale UN interdiction effort, as North Korean supplies and supply lines were subjected to UN bombing raids. This effort was not successful in stopping the North Korean supplies, and the North Koreans have also been praised by historians for the way in which they were able to maintain a supply network in the face of a massive bombing campaign. However, the North Koreans did suffer reduced supply because of this, and inefficiencies in transporting supplies from railroads to individual units negated the railroads' advantage. North Korean forces, though initially successful, were unable to counter UN forces with effective air defense, and were also unable to conduct successful interdiction of their own. This meant their supply network limited the combat actions that they could undertake; logistics could not keep up with units on the offensive, and North Korean units went almost completely unsupported during key engagements, reducing their ability to fight effectively. North Korean logistical inefficiency prevented them from overwhelming UN units in the Pusan Perimeter and enabled the defending UN troops to hold on long enough for a counterattack to be launched at Inchon. This landing, coming behind North Korean lines, had the effect of collapsing the North Korean front and ultimately ended the battle around Pusan in September.