Complex sentence: He saw service during the First World War, initially as Captain of HMS Vernon and then as commanding officer of the Battleship HMS "King George V", flagship of Admiral Jerram at the Battle of Jutland in May 1916.
Split into simpler sentences: He saw service during the First World War initially as Captain of HMS Vernon. As flag Captain to Admiral Jerram, he was commanding officer of the Battleship HMS "King George V" at the Battle of Jutland in May 1916.