The Colt Model 1903, aka Pocket Hammerless, aka Model M, was a massively successful design for Colt on the commercial market. It was chambered for the .32ACP cartridge, with a .380 model introduced in 1908. During World War Two, the US government took an interest in the pistol. A total of 17,330 were purchased in .32 ACP, and another 3,113 in .380 ACP. The .32 caliber examples are found between serial numbers 541,103 and 572,215. Some were purchased by direct contract, and some procured independently from dealers.

These were never used as combat pistols, but instead went to a variety of services and agencies. Primarily they were used for military police and intelligence services (the Office of Strategic Services), including a full third of them being sent to the UK for use by Special Operations Executive. One of the examples we have today is documented by Colt records as being delivered to OSS, in fact.

Around October 1944, several changes were made to the pistol:

- The sights were made larger, both front and rear.
- Slide serrations increased from 17 to 19.
- The finish changed from blued to phosphated.
- The "US Property" stamp font got slightly larger.