Sometime around 1939 - 1940, the US Army adopted a shoulder holster as an option for carrying the M1911A1 pistol. A similar version was adopted during WW2 for the S&W Victory Model and Colt Commando revolvers. These holsters remained in service at least until the 1990s, AFAIK. After the 1911 was replaced with the Beretta M9, it was used for the new pistol.
Several years ago I picked up a copy of the USGI M3 shoulder holster for the S&W Victory Model from the now-defunct Pacific Canvas and Leather. I like it a lot for carrying my Model 15 or Ruger Police Service Six, but of course it's too small for an N-Frame.
I recently replaced the grips on my S&W Model 28-2 Highway Patrolman, which made the gun much easier to shoot with my small hands. It previously wore a set of Herrett's Shooting Stars. I replaced them with a set of Thai Magnas + a BK Grips adapter. With it now fitting me better I started thinking about packing it as a woods gun.
So back on 9/3 I placed and order with El Paso Saddlery for one of their “1942 Tanker” holster, which is their version of the USGI M3 shoulder holster. It arrived 9/15, much sooner than expected based on what the EPS website says.
If it looks backwards it's because I'm a southpaw.
It’s very nicely made with nice leather, stitching, and hardware. They also threw in a key fob.
Out of curiosity I put my Colt Shooting Master in it and except for the fact that it’s too short for a 6” barrel, the holster fits the gun well. So, if I ever pick up a 4” Colt New Service this holster is usable with it.
A S&W Heavy Duty would look right in this rig.
I'm looking forward to using it in the woods.
I also have a copy of the M3 for 1911s. I don't have a 1911 anymore but I do have an M9, so tonight I tried it in the holster.
(I don't recall where I got this one from.
Maybe Amazon. I'm pretty sure it was made in India.)
It's very snug and takes quite a bit of force to insert. So, since the leather was dry I gave it a good coat of neatsfoot oil and plan to leave the Beretta in it for several days in the hopes it'll stretch out.
As-is, my Browning High Power and Beretta 81 Cheetah fit OK. The CZ P-09 won't fit at all.
I've recently run across variants of the Tanker holster cut like the leather ones but made from canvas. The Amazon link above has some. I've never tried them and they are a bit less expensive, but I've no experience with them. They might work well, might not.
I also ran across this blog post extolling the merits of the M7 shoulder holster. The M7 differs from the M3 in that it includes a chest strap to help keep it from flopping around. That post also lists a variety of pistols that will fit, which makes it close to being a universal holster.
As to why to use one, as noted above I find it comfortable. It also makes the gun available if you're sitting in a vehicle. The strap can be adjusted so you can wear it over your clothes or concealed under a coat. Also, if you can't normally carry a gun but want one that you can quickly throw on, it's an option.