The Colt Officer's Model is a double-action revolver with a medium frame, produced between 1904 and 1972 and which was mainly focused on sport shooting and of which four variants stand out: Officer's Model Target, Officer's Model Target Rimfire, Officer's Model Special and Officer's Model Match.
 
Colt introduced the Officers Model in 1904 as a medium frame "E" double action target revolver until production ceased in 1969.  This was Colt's premium medium frame revolver during this time period.
SN:644725 MFG:1950
 
More information here