While the 10th to 11th Century AD term ''Megus Doux'' has been mistranslated into The English form of ''Megaduke'', it actually meant ''Grand Duke''. It was a Title of responsibility associated with Commander-in-Chief of a Naval Force. Unlike the later term (Rank) ''Admiral'', The Megus Doux was also entrusted with command of any needed Naval Infantry (Ground Assault Force) or Army.
Several Campaigns in The Aegean were undertaken with moderate success by Megus Doux John Doukas, the first to hold this Titile in the late Byzantine Empire. By the 12th Century AD (The Fourth Crusades), The Byzantine Fleet would all but cease due to that War (thru loss and lack of proper replacement). The Title however was used as an honorific one. The later Serbian Empire (1346-1371), also adopted many Byzantine Titles. Their use of a ''Megus Doux would eventually be replaced by the previously discussed ''Voivode'' or Territorial Governor.