A question about navy service, early 1900s

[Annie65115]

I have sight of some Royal Navy papers for someone who joined up age 12 in 1905 and was finally discharged on medical grounds (no longer fit for active service) at the end of WW1.

He is nowhere to be found in the 1921 census but reappears on the marriage index in the 1940s.

This man was a Channel Islander and having served all his adult life at sea, I'd think the sea was in his blood. I'd assume he was back at sea for the 1921 census were it not for his having been medically discharged.

But could he have rejoined the RN under less stringent medical requirements once the war was over? Or would he have been able to join the merchant navy instead, having been medically discharged?

[philipsearching]

Can you find him on the 1939 Register?  This could help with his occupation.

Philip

[ShaunJ]

Have you looked for merchant navy records on FindMyPast?

[Annie65115]

I can't find him in the 1939 reg.

ShaunJ, you're right. There's something on FindMyPast -- filed under "Britain, Merchant Seamen, 1918 - 1941" - I presume this is merchant navy? But I'm not familiar with MN paperwork. It gives his name, dob, pob so this has to be the right man.
He looks to have been an asst cook. (he was down as "pastry chef" in 1915, so that's entirely possible).
It gives a number and a London office for unemployment insurance; what would this have been for?
Discharged from Britannic (must have been his ship?)
"DECLARATION TO BE MADE IF OCCASION ARISES" I hereby certify that I am not now in possession of an unfilled Continuous Certificate of Discharge (Board of Trade, irish or Canadian) for the following reason: 1st application (that latter handwritten). what does that mean?
dated 4 July 1941.

I see that Britannic was a troop ship in the 2nd world war. But staffed by merchant navy? Would that happen?
https://en.wikipedia.org/wiki/MV_Britannic_(1929)

It looks as though this may have answered my original questions but opened a few more!