David Sarnoff, the head of RCA,  ordered his engineers in marketing and
research to bring into production the previously developed RCA Victor 45 
RPM system (which had been kept a carefully guarded industrial secret for  
nearly 10 years). The first advertising for the new ’45’ system appeared in 
Billboard magazine in April 1949, and the first of the new 45 RPM discs
and automatic record players appeared in retail record shops in June 
of 1949.

David Sarnoff