ARPSC

The term "ham radio" was originally an insult, like ham-fisted. Around two million people worldwide are "hams" with 700,000 of those being in the U.S.  Technically, all early radio experimenters were in fact amateurs. What makes today's amateurs into Hams was WWI. Their radio broadcasting was suspended in 1917, and restored in 1919. This process was re-played in WWI. But in some ways it was that cessation and rebooting that codified what was ham and what was commercial by separating the services into casts.

In other ways it was its limited wartime use that let to it's modern function in emergency services. The first edition of the ARRL's (American Radio Relay League) Emergency Communications manual came out in 1940. But this was preceded slightly and less formally by a 1938 article in QST  titled 'When emergency Strikes." These ideas coalesced into formal policy and eventually a body of law. Hence the start of the ARPSC (Amateur Radio Public Service Corps). Their function is as follows:

"[To] maintain and continue to train and educate Amateur radio personnel interested in the advancement of communications and safety of citizenry in whatever systems may be available and in use within the Local, State and Federal Structure of ARES (Amateur Radio Emergency Service) and RACES (Radio Amateur Civil Emergency Services."

But what are they. the 1969 ARRL book describes them as a voluntary organization of licensed amateur radio operators sponsored by the ARRL.  Back then RACES was specifically for "civil defense communications." Some early documents give a dotted line to the Red Cross with reference to a memorandum. But modern versions of that document omit the ARPSC. It appears that in the early 1980s the ARRL quietly subsumed the ARPSC into ARES services. But the nomenclature lived on. There was already 5 decades of inertia behind that acronym.

There are a number of ARPSC groups still left across the country.Most have updated their paperwork to describe a continued connection to ARES, GEMO (Governmental Emergency Management Organization)  EMHSD (Emergency Management and Homeland Security Division) and any other vaguely federal sounding acronyms. they are still all volunteer amateur radio operator organizations committed to providing supplemental emergency communications as they always have.