Compact, slim, accurate, and simple. All mantras for the most modern concealed carry pieces today. They all apply to a design introduced 118 years ago as well – the Colt M1903.
While well-engineered semi-auto pistols abound today, the same statement simply wasn't true in the early 20th Century. Most early autoloaders were downright funky (see the Bergmann 1896), had bad ergonomics (Borchardt C93), were overly complex (C96 Broomhandle, which are notoriously hard to disassemble), and proved to be evolutionary dead ends (the Luger – not a lot of toggle actions in production these days).
Enter the gun guru of Ogden, Utah, Mr. John Browning, who largely hit it out of the park with his freshman semi-auto handgun, the FN M1900 of 1896, the first pistol with a slide – let that sink in. A simple blowback single-stack chambered in .32ACP – which he also invented – he followed that up in 1897 with his short-recoil operated Colt Model 1900, a larger gun whose action was recycled into the Colt M1902, which we have talked about before, then scaled down to make the Colt M1903.
While often billed as the "Pocket Hammerless" since, A) it was small enough to put into a coat pocket, and B) there was no visible hammer, the M1903 had a 3.75-inch barrel and an overall length of 6.75 inches. Designed for such concealed use, the gun has what today would be called a "carry melt" and has a minimum of snag-prone surfaces. Weight, loaded with eight rounds of .32 ACP, came out to 24 ounces. The asking price, when introduced, was $26, or about $700 today (blame FDR for taking the United States off the gold standard).
The M1903 compares well in size to the more familiar Glock 43, with the Austrian polymer entering the market in 2015.
The guns proved extremely popular with Colt. So much that the company introduced what today would be deemed a "magnum version" in the only slightly larger .380 ACP-chambered M1908. Keep in mind that, while many scoff at the .32 and .380 these days, and 1900s-era round-nosed ammo was even more anemic than what was available now, for its era it was still more potent than many black powder cartridges that were marketed for handguns that preceded it.
Both variants remained in production for a half-century, with Colt reportedly still shipping models assembled from existing parts as late as 1953. Over a half-million guns left the factory, making them common. They were used by the U.S. military in both World Wars, by the cloak-and-dagger OSS behind enemy lines before the invention of the CIA, and by numerous law enforcement agencies.
There was even a documented factory belt clip option, beating ideas like the Clipdraw and Techna Clip to the market by generations in a case of "everything old is new again."
Further, the slim Colt seems to have been extremely photogenic, having appeared in the hands of movie tough guys and not so tough guys for over a century, ranging from Charlie Chaplin (in 1918's Shoulder Arms) to Bela Lugosi (The Black Cat, 1934), Frank Sinatra (Suddenly, 1954), George C. Scott (Patton, 1980), Gabriel Byrne (Miller's Crossing, 1990), Denzel Washington (Devil in a Blue Dress, 1994), Mads Mikkelsen (Flame and Citron, 2009), Cillian Murphy (Anthropoid, 2016) and Keanu Reeves (Wick 3, 2019). Speaking of swagger, film noir legend Humphrey Bogart used an M1903 on screen in most of his best movies, including Casablanca, The Big Sleep, and Key Largo.