British Royal Navy Rear Admiral
Post WW1 monocles were associated with the upper class both in the twit variety and the intellectual. One suspects that it fell out of real fashion in WW1 as it must have been very dificult to keep one in place whilst scrambling in and out of trenches etc. OK for the staff officer perhaps.
This painting appears to one of a Royal Navy Admiral of the Fleet, Admiral, Rear Admiral, or Vice Admiral in Standard Service Dress.
December 10th 1941 –
Japanese troops sink Britain’s two main warships – the Prince of Wales and Repulse off the coast of Kuantan