Today, the California Commission on Peace Officers Standards and Training P.O.S.T. mandates police agencies conduct formal training for all sworn officers wishing to be P.O.S.T. certified.  It hasn't always been that way.  Prior to WWII, few U.S. police agencies had any formal training at all.  The Los Angeles Police Department began formal training officers in 1924. As illustrated below, the SDPD wasn't far behind.