Help needed on official numbers


I work in one of our careers offices and one of the perks of my job is we get all sorts of people coming through the door asking about past records etc.yesterday i had a gentleman visit and he was researching his father's naval history. I have given him plenty of info but hte one thing that has stumped me comple his official number was SR8012. No matter how i search on the net I just cannot work out where he joined up or how he got that number. He was an Ordnance Artificer and he served from Sept 40 until Nov 45.Anyone with any ideas about his number?????????????????