World War 1 Merchant Navy records

I have my grandfathers medal from his service in the Mercantile Marine in WW1 but unable to find service records.

The medal is the British War Medal 1914 - 1918.

It is inscribed with D. H. Bedford ORD. SMN R.A.N. B.

I am told he adjusted his birth date (27/04/1900) so he could help the war effort. He was born in 1900 and served from 1915 out of Brisbane.

Prior to WW1 the RAN was a coastal defence force. Then it became a blue water navy following its purchase of some capital ships like HMAS Australia. Might that account for the “B”: in your grandfather’s medal? Royal Australian Navy (Sea-Going). Just a thought. Hope you work it out.

Thank you Peter.
Sounds like much more research to do
Cheers