Thanks for your (and Richard's) explanation for us non-military and Army/Air Force types who don't understand these inequities. I could never understand the rank designations that include job description in the Navy. In the Army, a Sergeant, Specialist, Captain, was just a rank that determined pay grade, but in the navy, there are IT mates, and Corpsman's X-class and who knows what all. Nobody gives a whit what my MOS (Military Occupational Specialty) was. FWIW, it was 62G20, Quarry Machine Operator. I made little rocks out of big rocks.
It's not nearly as complicated as you think it is, Jim. In the Navy, pay grade rank is just the pay grade rank. (Enlisted E-1 through E-9 are Seaman (or Airman) Recruit, Seaman (or Airman) Apprentice, Seaman (or Airman), Petty Officer Third Class, Petty Officer Second Class, Petty Officer First Class, Chief Petty Officer, Senior Chief Petty Officer, and Master Chief Petty Officer.)
Where it gets complicated is adding the RATING to the rank, which is the technical wording for the job specialty. In the same way your MOS number specifically defined your job, in the Navy, adding a rating to a rank also made it very clear what that sailor did. I was a "Data Processing Technician First Class Petty Officer" for a large part of my career. That's a lot of words to define me, (or anyone), so they'd abbreviate a rating down to a few letters. In my case, a Data Processing Technician was called a "DP." So as a First Class Petty Officer, that made me a "DP1." Electronic Technicians were ETs. Boatswain's Mates were "BMs." Quartermasters were "QMs." Boiler Technicians were "BT's." Each rating was for a specific job, or type of job, within a larger category of work. At the time, there were over 100 different ratings, each with specific lettering abbreviations for the title, so it could get to be complicated. But still, not a lot different from a lot of MOS's that weren't familiar to everyone. The simplest thing to ask someone was "What does a [whatever rate] do?" Most sailors were happy to talk about their work.
Don't get me started on the different types of uniform insignia. That's a whole other kettle of fish. Or Squid, if you prefer.
Dave