“December 6, 1941
“On the American Continent in October the Army began training barrage balloon troops at Camp Davis, [Onslow County], North Carolina. Not only have they ordered four or five hundred balloons, but it is understood they are considering the use of these balloons in the defense of Hawaii and Panama…. Though investigations have been made in the neighborhood of Pearl Harbor, they have not set up mooring equipment, nor have they selected the troops to man them….There are no signs of barrage balloon equipment….
“Because they must control the air over the water and land runways of the airports in the vicinity of Pearl Harbor, Hickam, Ford and Ewa, there are limits to the balloon defense of Pearl Harbor. In all probability there is considerable opportunity left for a surprise attack against these places.”
— Cable from the Japanese consul general, intercepted Dec. 6 but not translated by U.S. naval intelligence until Dec. 8. (Barrage balloons, tethered by metal cables, were positioned to interfere with low-flying enemy aircraft.)