The Marine Corps Security Force Cadre Trainers,(MOS 8153) used them as did the NSF & ASFs, in the 70's, 80's & early to mid-90's.
The purpose for the Cadre Trainer Teams were to train the Naval Security Forces (NSF) and Auxillary Security Forces(ASF) on Naval bases where there were no Marine Security Force Companies (aka Marine Barracks) permanently assigned.
The Weapons in question were the blued 4" Ruger Service Six and to a much lesser extent the 2 3/4". Alot of the 4" version had lanyard loops on the butt, however, I don't recall the 2 3/4" having one. The std duty belt for the CTTs were a std web belt, Bianchi UM84R holster, and 2 speedloader pouches, each holding 2speedloaders and a std 10 rd shotgun pouch on the weak hand side.
Before the UM84R holster, a black leather "Border Patrol" type holster was used, either with the thumb break or the older retention strap type.
I might add that the Rugers used by the Marine CTTs were actually Navy Property not USMC property and the ammo was the std 130 gr FMJ, loaded by Winchester & Federal.