Beg to differ Adventure, but for the 11 years that I was in the Royal Navy, the Officer of the Day was always the " OOD ", the abbreviation "OD " being only used to denote the rating of Ordinary Seaman, and being, I think ,just a further contraction of " ORD" ,which was also much used. As to the song, I have always sung " Nobby Hall the BIG OD " , as that's what he ( Nobby ) was !! ( ie a total twat ! ).And what was I for those 11 glorious rum-soaked,Tiger-tangled, Commander"s Table visiting,punishment-serving years ?? Yes !! ---A Big OD !!    cheers ! Roger ( HMS EAGLE, 1966-1969 and RAF Changi, of course ).