Conway, New HampshireApril 1958

On April 19, 1958, the crew of a B-47 bomber flying near Syracuse, New York, spotted a round, silver object in the sky above them. The pilots and crew were at an altitude of 32,000 feet in excellent visibility. The object remained clearly visible for 20 minutes as the aircraft flew between Syracuse and a point about 20 miles southwest of Plattsburgh Air Force Base in New York. At first, the crew thought it might be a weather balloon, but the object's behavior was puzzling. It moved alongside the B-47 for roughly 12 minutes before the bomber pulled away, with the object disappearing from view only when the aircraft had traveled about 20 miles beyond Plattsburgh.

The investigation began quickly. An enlargement of the photograph taken by the crew showed a perfectly round, transparent object that resembled plastic balloons. Weather Bureau and Navy charts indicated that a high-altitude balloon was in the area at the time. Additional details emerged during follow-up interviews. A flight of fighter aircraft from Syracuse, flying at 20,000 feet at roughly the same time, also reported seeing an object that was high, stationary, and bright.

The Air Force investigators checked with balloon-tracking agencies. The Weather Bureau reported releasing only a small 100-gram pilot balloon from Niagara Falls at about 1:30 p.m., which likely broke within an hour. However, a detailed study of upper-atmosphere balloon trajectories determined that a high-altitude balloon designated S-393 had been released from Vernalis Air Force Base on April 15 and was being tracked across the United States by both the Air Force and civilian authorities at the time of the sighting. The balloon, over 130 feet in diameter, was moving slowly from west to east across the region and matched the object's description in size, shape, color, and behavior.

The Air Force concluded that the object was most likely balloon S-393. However, the file notes that the object's visibility over such an extended period and the crew's professional assessment that it did not behave like a typical balloon left some doubt. No definitive explanation appears in the case record. The full case file, comprising 44 pages as held by the National Archives, is reproduced below.