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The program first aired on June 17 1947 on NBC radio under the title The New Adventures of Philip Marlowe, with Van Heflin playing Marlowe. The show was a summer replacement for Bob Hope. The first episode adapted Chandler's short story "Red Wind". The NBC series ended on September 9th, 1947.
In 1948, the series moved to CBS, where it was called The Adventures of Philip Marlowe, with Gerald Mohr playing Marlowe. By 1949, it had the largest audience on radio. The CBS version ran for 114 episodes. That series ran from September 1948 to September 1950.
From 1951 July 7th to September 15, 1951, the program was a summer replacement for Hopalong Cassidy. Mohr played Marlowe in all but one of the CBS shows. He was replaced by William Conrad in the 1950 episode, "The Anniversary Gift".
Despite the program's popularity, it had no sponsor for most of its time on the air. The lone exceptions were when Ford Motor Company and, subsequently, Wrigley's Gum sponsored it during part of 1950.