Strictly speaking, The War of the Worlds is not a hoax as it was advertised as a piece of fiction in advance.
However, it still created the same sort of response as a hoax would have done because many listeners were caught off-guard.
Whilst younger people may think that The War of the Worlds was a movie starring Tom Cruise it was, in fact, originally a book by H.G. Wells.
When it was broadcast, as an episode of the American radio drama anthology series Mercury Theatre on the Air, all hell broke loose.
The War of the Worlds was aired as a Halloween episode of the series on the 30th of October in 1938.
Coming over the airways from the Columbia Broadcasting System radio network, it was voiced and directed by Orson Welles.
Despite the fact that it had been advertised in advance, many listeners were caught unawares, probably because they just randomly tuned in during the broadcast.