This is where you've lost me.
I am not the most academic person in the world, in fact, this very morning I have sat 2 exams (City and Guilds Level 2) in Maths and English, at my local DISC, the results of which will determine whether I can go on to a main site college and gain a place on an Access course.
I have very little education, and no knowledge of social history, but I am trying to improve my situation. It was perhaps, a little naive of me to attempt to piece together my family history, when I am sometimes unable to grasp the subject.
I thought that the codes were relevant in determining where he had spent his working life. Like I have said previously, I have attempted to find him on online crew lists at various sites, NA, FindMyPast, CLIP and have returned no results.
This is why I got confused with 'merchant' service, Navy or transport of goods on the sea. I think I might well leave this particular ancestor alone, it is I fear, much too difficult to fathom.
Thank you in your endeavours to help me

merseyclyder