In the first proven act of sabotage in the history of commercial aviation, a Boeing 247 operated by United Airlines exploded in mid-air near Chesterton, Indiana, killing all seven people aboard.

Sabotage is a deliberate action aimed at weakening a polity, government, effort, or organization through subversion, obstruction, demoralization, destabilization, division, disruption, or destruction. One who engages in sabotage is a saboteur. Saboteurs typically try to conceal their identities because of the consequences of their actions and to avoid invoking legal and organizational requirements for addressing sabotage.

The Boeing Model 247 is an early American airliner, and one of the first such aircraft to incorporate advances such as all-metal semimonocoque construction, a fully cantilevered wing, and retractable landing gear. Other advanced features included control surface trim tabs, an autopilot and de-icing boots for the wings and tailplane. The 247 first flew on February 8, 1933, and entered service later that year.

United Airlines, Inc. is a major airline in the United States headquartered in Chicago, Illinois that operates an extensive domestic and international route network across the United States and six continents with more destinations than any other airline. Regional service operated by independent carriers under the brand name United Express feeds its eight hubs and the Star Alliance, of which United was one of the five founding airlines, extends its network throughout the world.

United Air Lines Flight 23 was a regularly-scheduled flight operated by United Air Lines between Newark, New Jersey, and Oakland, California, with intermediate stops. On October 10, 1933, the Boeing 247 airliner serving the flight—registered as NC13304—exploded and crashed near Chesterton, Indiana, United States, en route from Cleveland to Chicago. It carried three crew and four passengers. All aboard died in the accident, 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 accident site 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.