TOP SECRET 7. Airfields. Hitherto the Communist jet fighters have operated from the safety of Manchuria. At this range they present a negligible threat to the area of the land battle. There are a number of jet airfields in N. Korea, which so far have been kept out of action by U.N. bombing, but if the Communists succeeded in operating from them they would be able to threats the battle area more seriously. 8. Navy. North Korean defensive mining continues. Various small Communist amphibious operations are attempted and carried out with determination.