These guys inhabit a small camp in Eastern Plaguelands, and will attack any hostile mobs kited into that area.
The camp itself consists of three groups of two of these soldiers, along with an https://vanillawowdb.com/?npc=16284 Argent Medic (who will cleanse you of diseases provided you are at least Honored with the Argent Dawn), and three injured infantry. One of the infantry groups patrol around the outside of the camp.
Useful to help kill tough mobs, if kited (e.g. https://vanillawowdb.com/?npc=12337 The Crimson Courier )