A live military "incendiary device" dating from the Vietnam era was found in the mail at O'Hare airport last week.
Chicago Customs and Border Protection officials were searching the outbound mail when they stumbled across the device. The package was destined for Japan and originated in Missouri.
The device is a "military training dummie" shipped from an estate sale that was sold online.
The U.S. Postal inspectors and Chicago Police Bomb unit labeled the device as a Phosphorous based trip flare M49A1. A trip flare was used as a warning signal when enemy troops arrived. The flare can reach up to 5,000 degrees Fahrenheit and provide a light intensity exceeding 35,000 candle power.
CBP director of Field Operations David J. Murphy said the discovery helped avoid a "potential catastrophic event."
The flare was rendered safe and destroyed according to a released statement. The situation is being investigated but CBP officials do not believe the involved parties had any malicious intent.