HG Wells wrote a book in 1898 detailing an alien attack on Earth. It was one of the first of it's kind, tying in current (for the turn of the century) scientific theories with an alien invasion and attack on the human race. Wells had studied as a scientist and like Neil Degrasse Tyson today, was widely known for his ability to explain scientific theories with a simplicity that everyone could understand. Although "War" was classified as science fiction and scientific romance, it's parallels to evolution, space travel, and the possibility of extraterrestrial life was based on the research of the time and inspired many scientists. Just 20 years prior Mars had been viewed for the first time through a telescope, and 30 years prior Darwin issued his theories of natural selection and evolution.
Original broadcast in full:
Orson Welles had primarily worked on the stage and in radio prior to the 1938 broadcast that brought him international fame. Basing the mood for the broadcast off the non-fictional Hindenburg disaster reports, Welles (and Howard Koch) reset the novel by placing it in New Jersey instead of England, and planning to deliver it as a breaking newscast interrupting the "live" broadcast of Ramon Raquello and his Orchestra (actually the in house CBS orchestra) with bulletins and commentary from scientists, witnesses, and members of the US Government (played by Welles and other CBS actors).
Howard Koch
The Mercury Theater on the Air program was one of few programs to air without advertisements. Welles had been a regular cast member for 3 years, and having heard Ronald Knox's BBC false broadcast of London riots a few years prior, was inspired to try a similar plot in the US. Without commercial interruptions and already in a heightened state of anxiety over attacks due to the looming threat of a second world war, listeners that joined the program mid-broadcast were unaware it was a work of fiction.
With sound effects (directed by Ora Nichols), "dropped" interviews, dead air, and a general sense of panic throughout the hour long broadcast, many listeners were thrown into a frenzy as CBS simulcasted their broadcasts throughout most major cities in the eastern US. Radio stations were flooded with calls from concerned citizens, and unrelated power outages in a handful of towns added to the confusion and fear. Although today we're told the hysteria wasn't as dramatic as originally reported, it's estimated that hundreds of thousands of people were genuinely terrified by the performance. Welles had anticipated listeners tuning in during breaks of other stations, and timed the most terrifying parts around these since the Mercury was a smaller production with fewer listeners and no stop sets. People turning the dial after the first scheduled commercial break in other station's programs (just like today, around 13 after the hour) initially caught War in the first report on an invasion over Grover Mills, NJ. After the introduction, no mention was made that the story was fictional until over 30 minutes in.
CBS Studio 10/30/38
The newspapers, threatened by radio, had a field day with Orson's performance. They claimed radio had too much power and was dangerous, suggesting everyone go back to print, as print "never deceives". Even Hitler cited the broadcast as proof of "the decadence and corrupt condition of democracy". The station was sued by hundreds, citing mental anguish and personal injury. All suits but one were dropped - a man had spent money reserved for new shoes on supplies to flee town - Welles insisted the man be compensated. Newspapers ran almost 13,000 stories and the station was investigated by police and FBI (then called the BOI). Koch told the NY Times - "The police came in after the broadcast and seized whatever copies [of the script] they could find as evidence - There was a question that we might have done something that might have criminal implications" .
Regardless of the mayhem caused, Orson Welles and CBS were skyrocketed into international fame. The broadcast has been copied numerous times all over the world: in the 1940's a Spanish DJ reenacted the story with help from a local newspaper, initially causing fear in Ecuador that led to police being dispatched. Once it was revealed the story was fictional, a riot broke out against the station and newspaper that played party to the hoax.
To this day Welles' War of the Worlds broadcast is cited as one of the most famous moments in radio history, and you can often hear the broadcast re-aired around this time of year. Welles was only 22 at the time, and the fame garnered almost immediately launched his Hollywood career.
"This is Orson Welles, ladies and gentlemen, out of character, to assure you that The War of the Worlds has no further significance than as the holiday offering it was intended to be; The Mercury Theatre's own radio version of dressing up in a sheet and jumping out of a bush and saying "Boo!". Starting now, we couldn't soap all your windows and steal all your garden gates by tomorrow night, so we did the next best thing. We annihilated the world before your very ears and utterly destroyed the CBS. You will be relieved, I hope, to learn that we didn't mean it, and that both institutions are still open for business. So goodbye everybody, and remember please for the next day or so the terrible lesson you learned tonight. That grinning, glowing, globular invader of your living room is an inhabitant of the pumpkin patch, and if your doorbell rings and nobody's there, that was no Martian, it's Halloween!"
Welles apologizes for the misleading broadcast:
was an all around radio man who's decade spanned over 30 years, and appeared in over 10,000 broadcasts in all forms of production from sound effects to leading man. As a current day radio employee, this book just makes me want to buck the system, bring in some actors and some musicians, pull up a script, lock the studio door, and have a blast. 
. The book starts out as a behind the scenes look into the greatest era of radio, but about halfway through, tragedy strikes. And by tragedy, I mean 
and the Red Channels list.