Such a radar incident occurred at one of our defense installations in Alaska early in the morning of January 22, 1952[VIII-2]. Shortly after midnight a bright target appeared on the radarscope, moving down from the northeast, fairly high, and apparently traveling at about 1500 miles an hour. Unidentified targets require particularly prompt investigation in this sensitive area so close to Siberia. Within minutes an F-94 jet was moving in from a fighter base 100 miles to the south; two other jets were scrambled at intervals and vectored in toward the unknown target by ground radar. When radar switched to short range, however, it always lost both the target and the pursuit plane, even though both were close to the radar site. The first jet could find nothing in the air, and no echoes appeared on its radar. The second jet saw nothing in the air, but its radar recorded a brief, weak echo to the right at about 28,000 feet. The echo faded immediately, returned briefly, and then disappeared as the jet closed in. The third jet, after cruising the area for ten minutes without detecting anything visually or on radar, suddenly got a strong radar return from an apparently stationary target just as it passed over the ground radar site. The pilot made three direct runs on the unknown. Each time he broke off the intercept when he got within 200 yards of the target position as shown on his radar, for fear of collision. At no time did he see anything at the supposed location of the target. (This experience is somewhat analogous to that of our man who used echoing sound waves to locate a solid structure only to find, on reaching the indicated spot, that the structure was not there.) Captain Roy James, chief of the radar section of ATIC, examined all the data and the scanty weather reports then available for this Alaskan area, and concluded that the targets were ghost returns probably from the ground, caused by peculiar atmospheric conditions--the same conditions that had interfered with normal operation of the ground radar. Although ground structures are scarce in that part of Alaska, they do exist, and so do mountains. The analysis was undoubtedly correct, even though knowledge of the location and movement of the temperature inversion was too imprecise for the analyst to plot and locate the true target that produced the reflections[VIII-3, p. 167]. Some of the nation’s most brilliant physicists have carried out fundamental research into the behavior of microwaves under varying conditions. The technical nature of these investigations makes them difficult to describe in ordinary language, but they provide vital information for the expert.