X Minus 1 and its antecedent, Dimension X, broadcasted the best science fiction radio dramas in the United States. From 1954 through 1958 some of the best science fiction short stories, like the Veldt by Ray Bradbury, came to life first in these dramas.
Many great writers wrote radio-plays or allowed their works to be adopted for the show (see parial list below). Science Fiction was in its infancy on television, and America lagged behind Britain, who had Quartermass and Avengers around this time. It wasn't until The Twilight Zone in the early sixties that a serious science fiction drama came to US television.
The mid fifties were the waning days of radio drama, as soap operas and situation comedies made an easier, and cheaper, transition to televison.
I've provided a link to archive.org to get the files or listen to the streams, as the files are too large to upload to free transfer services.
Here is a list of some of the more famous epidoses of X Minus 1:
The Colony and The Defenders by Philip K Dick
Universe by Robert Heinlein
Mars is Heaven by Ray Bradbury, and the Veldt from Illustrated Man is performed as a radio drama.
Adaptation of Nightfall by Isaac Asimov
The Reluctant Heroes by Frank M. Robinson