The first episode of Dragnet, no longer available, aired on June 3, 1949.  Below are the OTRR notes on this episode. Also included is an audo file summarizing and introducting the Dragnet series.

49/06/03 001 Dragnet, June 3, 1949. "Production #1." Program is not available

First Line: 

First Line Narrative and Plot: format not used on this episode 

Plot Extension: George Slocum - Thief

Cast: expected, Jack Webb, Barton Yarborough, Charles McGraw 

Listen to the series introduction created and disseminated by the Old Time Radio Researchers Group.

Episode 2: Nickel-Plated Gun

This podcast replays all available radio episodes of Dragnet, in chronological order.  Each weekend, the next two episodes are released.