What was the purpose of the higher Specialist ranks?

Sp4 Byron Skinner. Getting rid of the specialists rank was very dumb on the part of the Army and very expensive. Making all E-5's NCO and sending them through the schools and all the other crap a Sgt has to do is crap to some if not many soldiers most likely why the leave the Army after a single enlistment. The Specialists opens up jobs to MOS's like armor where many drivers and gunners were spec 5's, Medics where many of the Medics serving with line units were Spec. 5 or 6, head cooks wet often Spec 5's, Infantry Crew Served Weapons such as mortar and machine-gun held Spec 5 rank. The highest Specialist Rank I saw was I think a Spec 8, it was worn on an EOD Specialist. Spec 7's were not uncommon for Mess Sgts. of a Battalion Consolidated Mess, consolidated Meses were rare nearly all including Regimental HQ Company has their individual Mess facilities and no civilian workers all soldiers…This is something that should be brought back.

Many great repsonses. Mine is not unique but is illustrative. Three preople in this story. 1) My dad was an Army helicopter mechanic in the 1960s (including a tour in VietNam as a Huey Crew Chief), he turned down "hard stripes" so he could keep working on helicopters. Less than 30 years later I was a brand new aviation lieutenant; 2) my first platoon sergeant was a great leader, helicopter mechanic, and trainer of helicopter mechanics (I hope I learned alot from him). His replacement was not as well rounded, 3) that E7 could fix helicopters but couldn't teach. One particular time I saw him fixing a helicopter while 3 E4 and an E3 watched. Three years later I met him again on the flight line at Ft Rucker, he was working for the maintenance contractor doing what he did well - fixing helicopters.

As I understood it as the army was getting so technical in 1960 (don't laugh) they needed a way to promote specialists as they progressed but not give them leadership responsibility. When I came in 1970 I met my first and only Spec7. In 1975 As a SSG I was given all the Spec6s and 5s while we were in the replacement station.

The SPC was more of a rate then a rank. It was for Non Combat Arms MOSs. They did not have the same duties as an NCO.

1st, you'll notice no CSM in your picture. When I 1st came in, SPC5 and SPC6 was still a thing, but being discontinued.
The reason behind the specialist ranks was due to MOS's. SPC5 and SPC6 didn't really exist with a combat MOS, but was useful for say a mechanic. It was a way for commanders to promote outstanding soldiers without putting them into leadership positions. Personally I think it should have stayed. Look at promotion points and how high they can be for people in support MOS's. If the SPC5 and SPC6 rank was available soldiers could be promoted on merit instead of points.
The downside to the structure, a CPL/E4 outranked a a SPC6. Having said that, I had an SSG who was great at his job, but was chewed up as a leader. His was a case where the specialist ranks would fit nicely.

As an aviator (67N) I was ultimately promoted to SP5 as that was the authorized grade for a UH-1 crewchief before the Army decided they didn't have enough hard stripe NCOs in 1976 so I was automatically converted to Sgt. I knew several SP6's as they were all Technical Inspectors for our aircraft and they too were auto converted around the same time. The specialist did the technical work without the need for the authority. Our platoon sgt's were the standard SFC hard stripe rank.

I was a SP5 before making SGT during my enlisted and NCO service. The original higher Specialist ranks were mainly devoted to technical specialties outside of the combat arms. I was a cryptologic voice intercept operator (Russian) 98G when I was promoted to SP5. Later, when I took charge of soldiers in a leadership position, I received SGT's stripes. I cannot recall ever seeing a SP7 or higher...they were pretty rare...

I served in the Army Security Agency as a Communication Security Analyst on active duty from 1955-1958 and inactive until 1963, recalled one day and discharged. Like so many of our records in the old ASA many of mine have been fallen down the memory hole. If I recall correctly I was a SPC4 but since I have no DD214 I operate on a DOD form that shows my active duty time and that I was Honorably Discharged but it does not say when. The DOD lists my "Permanent Rank" as "Specialist Third Class" and that is a rank I don't ever remember seeing or hearing of before I saw in on the DOD records form. Anyone else ever hear of the SP3 rating?

Designed to recognize technical attainment, but not NCO responsibilities. Helped with the up-or-out philosophy by retaining technically qualified personnel at senior enlisted levels - but not requiring them to be responsible for troops like hard stripe NCOs. Some switched over to hard stripes and some ended up leading support troops.

I'm assuming your grandfather served in the mid 50s.... I suddenly feel comparatively old. My grandfather served in the Army Air Corps. I joined a little late in the year 2000. (I could have joined in '96.) There was a lot of talk about the SPC rank structure when I was in air defense (14E). I later became a medic 91W/68W. I had a senior NCO that was a 63S who knew a SPC6.