The difference is illustrated thusly:
- the license requirement differs:
- The ARES requires an amateur license, The ACS does not: ARRL EC Manual FSD-9 (187) section 4.1, paragraph 3: "Every licensed amateur is eligible to be an ARES member. Those without an amateur license are not eligible". The ACS does NOT require an Amateur Radio service license.
- Historically, the ARES is a service for licensees who want to operate their radios in times of emergency. The ACS views the situation differently and does more than just provide radio operators. An ACS unit can include Civil Air Patrol communicators, computer systems specialists, broadcast and television system personnel, satellite and microwave engineers, to name just a few of its participants. Yet, most of those in the ACS are, or often become, Amateur licensees as they discover the fraternity and benefits of Amateur Radio.
- the relationship differs:
- the ACS is an arm of local government. It serves as unpaid staff of that government in an on-going in-agency relationship. This relationship is considerably beyond that of a RACES unit that only expects to be utilized after an emergency occurs, or one that limits its participation to the Amateur frequencies.
- the ARES is an arm of an outside private group. It may or may not have the same goals as does the government. It does not have the on-going unpaid-staff relationship with government. However, exceptional ARES units may achieve an on-going role with local government. Also, where local ARES leaders have the will to do so, they could function in the ACS mode.
- the function differs: The ARES function is to supply radio operators for use via Amateur Radio. The ACS function is to fulfill communications related needs within government. That includes the use of Amateur Radio, but that is not the entire purpose or the limiting factor for the unit.