Would Charles Madden have taken over the Grand Fleet if something happened to Jellicoe?
Short answerYes; Madden was Jellicoe's number two, with Sturdee and other senior officers incorporated into a well-defined succession plan.
NotesCharles Madden was Jellicoe's immediate deputy and places Sturdee in the next tier of succession, with further senior officers also accounted for. The important point is institutional: Jellicoe prepared a clear command sequence and ensured that the fleet understood it. That planning reduced the risk that losing a commander during a major action would paralyze the Grand Fleet.