Dragnet, created by Jack Webb, a popular detective show of the 1950's actually premiered on the radio, with low expectations.
Jack Webb also played the title character, Joe Friday, in both the radio and television premier.
The origins of the show comes from Webb's role as a forensic scientist, working with police in He Walked by Night, a 1948 film based on the murder of a California Highway Patrol officer.
Webb became friends with Marty Wynn, an LAPD sergeant, who was a technical adviser on the film. They developed a theory that daily activities of the police could make a powerful drama, without melodrama, or exaggeration.
He began attending Police Academy courses, and tagging along on night patrols, trying to learn the ins and outs and jargon that would make the show more appealing.
Having already starred in one short lived detective show Pat Novak for Hire, when he pitched the show to NBC, they were leery of yet another private detective show. However, based on his prior show, they agreed to a limited run of Dragnet.
Seeking the approval of the LAPD, to use case files for a realistic depiction, William Parker, then police chief, offered the endorsement in 1950, providing that police not be shown in a negative light. This caused some arguments, because the show would not be allowed to discuss any hint of police corruption or, specifically, LAPD's racial segregation policies at the time.
The show debuted on July 7th, 1949. The first few months slowly evolved, changing the characters from the initial brash and forceful personalities, to the deadpan Friday, and the fretting Sergeant Ben Romero.
The show opened with announcer George Fenneman stating, "The story you are about to hear is true; only the names have been changed to protect the innocent".
Hal Gibney followed, describing the events of the case to follow.
The sound of footsteps led to a door closing. Joe Friday began the opening with the date, the weather, and who he and his partner were. Years into the radio program, and again into the television show, this opening rarely varied.
The radio show lasted 30 minutes. During this time they investigated the crime, pursued suspects, and often solved the case. Sometimes, the case was left unsolved and Webb himself said "We don't even try to prove that crime doesn't pay ... sometimes it does".
The ending was narrated by Hal Gibney, who announced the fate of the suspect.
The radio shows are available online here, allowing you to compare these shows to the later television premieres in 1952 and 1967.