the Tower Hill Memorial, London. Official Numbers and Code Letters Official Numbers were a forerunner to IMO Numbers. Empire Byron had the United Kingdom Official Number 169005 and used the Code Letters BCTG. References 1941 ships Ships built on the River Wear Empire ships Ministry of War Transport ships Steamships of the United Kingdom Ships sunk by German submarines in World War II World War II shipwrecks in the Arctic Ocean Maritime incidents in July 1942