Herbert Schmidt revolver
(The following info is from a page that I cannot link to, due to the rules here and what is on that page; a search for any of the below phrases will probably allow you to find it)
"Herbert Schmidt of Ostheim an der Rhon Germany. Schmidt has marketed firearms under a long list of trade names in Europe and the USA including Deputy Marshal, EIG, E8, PIC, Geroco, Madison, Bison, Omega, RG, AMCO, Spesco, Valor, Liberty, LA's Deputy, Liberty Scout, Deputy Magnum, Deputy Adjuster, NATO, Western, Burgo Mod 21, Gecado Model 21 , Indian Scout, VOL, Eusta, Cheyenne Scout, Texas Scout, and Buffalo Scout. The basic Schmidt pattern was a six-shot double action solid frame revolver, with a swing-out cylinder and a short barrel. Schmidt's other principal pattern was a western-style .22 revolver with either no ejector and a removable cylinder arbor, or with a rod ejector beneath the barrel. All Schmidt revolvers have the maker's name stamped into the lower edge of the butt grip frame, visible when the grips are removed. As with Em-Ge, Schmidt revolvers were also widely sold in the USA before the passing of the Gun Control Act of 1968.
Same Gun, Different Name: The German Manufacture Small Frame Single Action is imported under various names including: Hawes, Deputy Marshall, Western Duo, Herters, Buffalo, Texas Scout, Omega, Excam TA-22, HS-21, Geroco Liberty 13, Kimel and Guy Jones, and many others"
I don't think it was a training revolver; the manufacturer/importer just used "NATO" as a rather strange model name.
Other info at these links: