Michail,
Just read your post and I think you`ve got your wires crossed somewhere.(Sorry to say)
The red ensign (duster)is the flag used for the British Merchant marine and has been in use since 1864, the white ensign is used exclusively by the the Royal Navy. The blue ensign is a much more complicated issue, it can only be flown on Merchant ships under certain circumstances:-
If the Captain is a member of the Royal Navy Reserve (RNR), having RNR Officers and rating on board add holding an Admiralty warrant, Royal Fleet Auxiliary,Customs, Coast Guard etc.
However I`ve found one other group that can fly the blue ensign The Royal Hospital Group. I`ve never heard of this before, but Britannic was a Hospital Ship, so maybe she was part of this group, or any of the above groups and was flying the Blue Ensign. Does anyone out there know ??
Hope you are not miffed at this correction I mean no offence .
Cheers and Best Regards
Dennis