The advancement through the branch is REM2, REM1, LREM, POREL, CREL. That's Radio Electrical Mechanic Class 2 & 1, Leading Radio Electrical Mechanic, Petty Officer Radio Electrician and Chief Radio Electrician.
Hope this helps a bit, it's biased towards my time in the 60s and 70s. WW2 designations may well vary.