Project Blue Book Case #358. On April 24, 1949, a balloon tracking crew from the White Sands Proving Ground, stationed near the small community of Arrey, New Mexico, observed and tracked an unidentified object using a theodolite — a precision optical instrument designed for measuring angles in horizontal and vertical planes. The crew was engaged in tracking a weather balloon when they noticed a whitish, elliptical object at a much higher altitude, moving rapidly against the wind.
The object was tracked through the theodolite, providing precise angular measurements of its position and movement over time. The crew — experienced in tracking missiles and balloons — estimated the object was traveling at extremely high speed and altitude, far beyond the capabilities of any known aircraft. The elliptical shape and high-speed trajectory were inconsistent with any balloon or missile test being conducted at White Sands.
The Arrey case was considered one of Blue Book's most technically significant early cases because of the instrumented tracking data. Unlike purely visual sightings, the theodolite measurements provided quantifiable data about the object's angular velocity and apparent trajectory. The crew's professional competence in tracking fast-moving objects — their literal daily job involved tracking V-2 rockets and other missiles — made their observations exceptionally credible.
Project Grudge investigators could not explain the object. The case was classified "Unknown" and is frequently cited as one of the strongest early Blue Book cases due to the trained observers and instrumented tracking data.