Service gun's I've had several. My department didnt issue firearms. We had to buy our own. We could get anything we wanted... as long as it was a blue steel fixed sight .38 spl, 4" barrel... manufactured by Colt or Smith n Wesson. Later on the Rugers came on line and they authorized service six revolvers. A little later they got real jiggie and authorized stainless steel revolvers, and a bit later authorized stainless steel revolvers with 3" barrels.
My first service gun was a S&W model 10 4" blue (nickel was a no-no)
My next addition to my service revolvers was a 3" R/B stainless S&W. They actually made uniform service holsters for it.
The department started to go with autoloaders. We had a choice of a DAO S&W, a DAO Sig, or the Glock 19. I went with the Glock 19. My service revolvers also remained authorized and I was able to switch up when the mood struck me.
Funny thing... When Police women changed titles and became police officers and were put on routine patrol like the males they were authorized 3" barrel, squair butt, model 36's. Yep five shot service revolvers. They even made teeny tiney service holsters for them. As new female officers were hired, and most opted for full sized service revolvers the rules changed, and all females had to get a model 10. colt O/P, or a ruger service six.