Creeping around an underground labyrinth filled with booby traps and hidden dangers armed only with a .45. You just defined a Tunnel Rat.
As covered in the above 1967 short film by the Army, soldiers deployed to Southeast Asia poke around a newly discovered tunnel complex in an effort to reap any intelligence that may have been left behind by the (hopefully) former Viet Cong occupants.
Equipped with an M1911A1 and a Fulton MX991/U anglehead flashlight that put out an impressive 5 lumens of moonglow, so-called Tunnel Rats squeezed down the narrow underground passages that could contain high-value targets including bunkers, headquarters and storage facilities located near, or in some cases even under, American and Allied installations.
But there were efforts to provide a more purpose-built handgun for the job.
In 1966, the Army made a half-dozen tunnel rat kits that included a suppressed Smith .38 with downloaded ammunition for use by these underground gladiators. However, they weren’t liked and weren’t really all that silent due to the escaping gas from the cylinder.
Another attempted solution was the 1969-era Quiet Special Purpose Revolver, a Smith & Wesson Model 29 .44 Magnum that was chambered for a very low power .410-ish shell filled with 15 tungsten balls in a plastic sabot. Since the ammunition itself had about as much powder as a 4th of July party popper, the gun was fitted with a short smoothbore barrel and did not need a suppressor. Just 75 of the guns were made.