The story starts with the Colt Army Special, introduced in 1908.
The Army Special was the perfected version of the original Colt swing-out cylinder gun, the Colt New Army and Navy Models.
It's not remembered today, but Colt actually invented the swing-out cylinder double action revolver.
It's the Army Special that was the "grand daddy" of all the mid-frame Colt's to follow, right up to the Colt Python.
The basic action, frame size, and cylinder were used to build all the Colt mid-frame revolvers like the Officer's Model target revolvers, the Post-war Trooper, the 357 model, and the famous Python.
The Army Special name was wishful thinking, since the Army never bought it, so in 1927 Colt renamed it the "Official Police".
That's just what the gun became: THE "official" police revolver for at least the first half of the century.
The Official Police was the revolver of choice of the majority of American police departments, including New York City, the FBI, and most other larger agencies in the pre-war years.
It remained quite popular up through the 1950's with many departments, and it continued to be used up through the late 1960's.
It was available in barrels of 2", 4", 5", and 6", with other lengths and heavy barrels available on request.
Finishes were bright blue and bright nickel.
Calibers were 32-20, 38-200 British, .41 Colt Long, .22LR, and it's most popular chambering the .38 Special.
The Official Police was made from 1927 to 1969 when it was finally discontinued along with all the other old-style mid-frame revolvers, except the Super Premium Python.
Changes to the gun were so few over production, that parts from the 1908 Army Special will still interchange with a 2004 Python, which uses the same action and most parts.
The Official Police had a generally stronger frame and cylinder than the competing S&W M&P "K" framed revolver with it's smaller cylinder and lighter frame.
In addition, the Official Police had a reputation for being more accurate than other brands.
This was due to Colt's high quality barrels, and the famous "Bank Vault" lock up that perfectly aligns the cylinder chamber with the bore.
Before the war the mid-frame revolvers were called "the 41 frame" by Colt, since the gun was based on the New Army and Navy revolver in .41 caliber.
After the war, Colt started assigning letter codes to their guns, and the mid-frame was named the "E" frame.
After a few minor changes in the mid-50's, it was re-named the "I" frame.
Most people identify these post war Colt mid-frames simply as the Colt "E & I" frame.
Due to the complex 19th Century design, with it's tiny working surfaces and very definitely convoluted action, it's strongly recommended that ONLY true Colt-qualified personnel attempt to work on or adjust the gun.
Few modern gunsmith's have any experience with these complex "watchmaker's" guns, ands often wind up doing more harm than good.
Repair facilities like Colt, Pittsburgh Handgun Headquarters, and Cylinder & Slide are qualified and are preferred.