OSS "Stinger" Covert Cigarette Guns
During World War Two, the OSS (Office of Strategic Services) was the primary US clandestine operations organization. It was responsible for making all sorts of unique weapons, including these "Stinger" cigarette guns. They were single shot disposable .22 Short pistols.
The first pattern was contracted and manufactured entirely by the OSS, and 25,000 of them were manufactured early in the war. They proved to have a myriad of minor to moderate problems, though, including failures to fire and burst barrels. A second version was produced by the Ordnance Department in 1944, with a strengthened and improved design, and 25,500 of those were made.
I have not found any documentation of these being actually used, but then again not much documentation exists on the use of any OSS weapons. These sorts of things were often provided to infiltration agents who might never be heard from again, or dropped to partisan or resistance groups who weren't exactly writing field reports on their gear.