Project Blue Book Case #139. On April 5, 1948, an unidentified object was observed at Holloman Air Force Base, New Mexico — the second Blue Book unknown from this missile and aerospace research installation (the first being Case #2150 from October 1952, which despite a higher number occurred later). Holloman was among the Air Force's primary centers for guided missile testing and high-altitude research.
As Case #139, this was one of the earliest entries in the Blue Book archive, predating the formal establishment of Project Sign by just three months. The Tularosa Basin — bounded by the San Andres and Sacramento mountain ranges — provided a natural outdoor laboratory for missile testing, with White Sands Proving Ground immediately to the west.
April 1948 was a critical period for the Air Force's nascent UFO investigation. The program was just getting organized, and early cases from sensitive weapons testing facilities received careful attention. The case was classified "Unknown."