Calling all Cars ran from 1933-1939. It's generally considered to be the inspiration for the old time radio great, Dragnet. Calling All Cars chronicles the L.A. Police Department cases. Although this is an earlier version of the same type of show Dragnet was, there are some differences.
Calling All Cars was introduced at a time when Americans became much more mobile because of the automobile. Criminals could get into a waiting car, and if they got lucky enough, get lost in traffic! Dragnet came out much later, but they both gave a thorough and detailed account of the crime and the criminals behind the crime. Although during the time that Calling All Cars aired, criminals were sometimes glamorized, like Bonnie and Clyde and John Dillinger. Whereas during the later police and crime shows that aired on old time radio, that wasn't so much the case anymore.
With Dragnet in mind, there is another major difference, Dragnet used the same Police Officers each episode. Calling All Cars used different Police Officers each episode. There were only two recurring characters in Calling All Cars, the narrator Charles Lindsey, and real life LAPD dispatcher Jessie Rosenquist.