I think Goudie has it correct here. The Tech Apprentices, entry number (at Halton anyway) was in the 100 series, Craft Apps 200 and mech Apps 300. The Tech Apps did 3 years in training, covered 2 if not 3 trades and passed out on successful completion of the course as Corporals. Craft Apps, like me , were single trades, 2 years and passed out as Junior Technicians. The Mech Apps did one year and passed out as SACs. I also believe that the Technician Apprentice was envisioned as a "super" tech, and designed as a multi function fault finder, at line level, for TSR2. Perhaps others will know better.
Smudge
