On October 10, 1933, United Air Lines Trip 23, a Boeing 247 airliner operated by United Air Lines and registered as NC13304 crashed near Chesterton, Indiana, United States. The transcontinental flight carried three crew and four passengers and originated in Newark, New Jersey, with its final destination in Oakland, California. It had already landed in Cleveland, and was headed to its next stop in Chicago when it exploded en route. All aboard died in the crash, which was caused by an on-board explosive device. Eyewitnesses on the ground reported hearing an explosion shortly after 9 pm and seeing the aircraft in flames at an altitude around 1,000 feet (300 m). A second explosion followed after the aircraft crashed. The crash scene was adjacent to a gravel road about 5 miles (8 km) outside of Chesterton, centered in a wooded area on the Jackson Township farm of James Smiley.
Investigators combed through the debris and were confronted with unusual evidence; the toilet and baggage compartment had been smashed into fragments. Shards of metal riddled the inside of the toilet door, while the other side of the door was free of the metal fragments. The tail section had been severed just aft of the toilet and was found mostly intact almost a mile away from the main wreckage.
The Federal Bureau of Investigation declassified 324 documents related to the investigation on November 16, 2017. It is notable for being the first proven act of air sabotage in the history of commercial aviation.