The Mars was at Trafalgar, the Agamemnon was not. The song is discussed in detail HERE The song was on the DT twice, once as "Mars Forevermore," but the second one seems to have been removed. It's really Dick Holdstock's song (as Lloyd seems to be no longer with us), and he probably has recorded it. I still think it goes "Oh Agamemnons so," "Agamemnons" being the crew of a ship Nelson commanded. It's really about Trafalgar, not about the ships.