Complex sentence: The opening stage of the British counter-attack Operation Compass was known by the Italians as the "Battle of the Marmarica" after the name of the coastal plain where the battle was fought.
Split into simpler sentences: The opening stage of the British counter-attack Operation Compass was known by the Italians as the "Battle of the Marmarica". The "Battle of the Marmarica" name was derived from the name of the coastal plain where the battle was fought.