It can take time for Emergency Medical Services (EMS) to arrive on scene. During that time law enforcement officers may be the only medical care available. So officers need to be trained to supply that care.
The scene is a fixture in many war movies. A wounded soldier cries out, “Medic!” then another soldier, one who carries a medical kit and not a weapon, crawls out from his foxhole and braves the fury of a firefight or an artillery barrage to render aid to his wounded buddy.