The War of the Worlds broadcast
On 30 October 1938, Orson Welles and the Mercury Theatre aired a radio drama about a Martian invasion of New Jersey, followed by long-running reports of panic.
NPR records that Welles and his troupe took to the air on the evening of 30 October 1938 with an announcement of Martians landing in New Jersey. Wikipedia describes the programme as an installment of the Mercury Theatre on the Air radio series, aired at Halloween, broadcast live at 8 pm ET over the CBS Radio Network. Welles directed and narrated this version of H. G. Wells's novel.
Smithsonian Magazine says listeners across the country heard what sounded like a report of creatures and machines of war advancing on New York City, and that the broadcast was Welles's radio play. Wikipedia says the episode is infamous for convincing some listeners that a real invasion was under way. NPR says later stories describe a mass panic caused by the broadcast, and that the real picture may differ.
""The War of the Worlds" was a Halloween episode of the radio series The Mercury Theatre on the Air which was broadcast live at 8 pm ET on October 30, 1938 over the CBS Radio Network. The episode was directed and narrated by Orson Welles as an adaptation of H. G. Wells' novel The War of the Worlds and is infamous for inciting a panic by convincing some members of the listening audience that a Martian invasion was actually taking place."
- 75 Years Ago, 'War Of The Worlds' Started A Panic. Or Did It?, NPR (2013)
- The Infamous War of the Worlds Radio Broadcast Was a Magnificent Fluke, Smithsonian Magazine