The auxiliary is the element of the resistance movement established to provide civilian support for the guerrilla force. The auxiliary serves many of the same functions that combat service and support units do inside the US Army. The auxiliary's primary focus is on providing security, intelligence and logistical support for the guerrilla force using civilian supporters of the resistance. The auxiliary conducts clandestine support functions by organizing its people on a regional, district, or sector basis (which depends upon the degree to which local guerrilla forces are organized or not organized). Auxiliary members usually screen all new potential members of the underground. For reasons of operations security (OPSEC), all auxiliary functions must section themselves off from each other (compartmentalization) and from the guerrilla force through the use of clandestine communications techniques (ie dead letter drops, etc.).