From Wikipedia:

Dragnet was perhaps the most famous and influential police procedural drama in media history. The series gave millions of audience members a feel for the boredom and drudgery, as well as the danger and heroism, of real-life police work. Dragnet earned praise for improving the public opinion of police officers.

Actor and producer Jack Webb's aims in Dragnet were for realism and unpretentious acting. He achieved both goals, and Dragnet remains a key influence on subsequent police dramas in many media.

The show's cultural impact is demonstrated by the fact that even after five decades, elements of Dragnet are known to those who have never seen or heard the program:

* The ominous, four-note introduction to the brass and tympani theme music (titled "Danger Ahead") is instantly recognizable (though its origins date back to Miklós Rózsa's score for the 1946 film version of The Killers).

* Another Dragnet trademark is the show's opening narration: "Ladies and gentlemen: the story you are about to hear is true. Only the names have been changed to protect the innocent." This underwent minor revisions over time. The "only" and "ladies and gentlemen" were dropped at some point, and for the television version "hear" was changed to "see". Variations on this narration have been featured in many subsequent crime dramas, and in satires of these dramas (e.g. "Only the facts have been changed to protect the innocent").

The original Dragnet starring Jack Webb as Sgt. Friday ran on radio from June 3, 1949 to February 26, 1957 and on television from December 16, 1951 to August 23, 1959, and from January 12, 1967 to April 16, 1970. All of these versions ran on NBC. There were three Dragnet feature films, a straight adaptation starring Webb in 1954; a TV-movie produced in 1966; and a comedy spoof in 1987. There were also television revivals, without Webb, in 1989 and 2003. A newspaper comic strip version of Dragnet, written by Jack Webb and Joe Scheiber, ran in newspapers from about 1952 to 1955.