Complex sentence: The change in the use of carriers from single or paired carriers with support vessels to task groups of three or four carriers was a Mistcher idea, which he instigated for the purpose of concentrating the air groups for a better defense of the carriers.
Split into simpler sentences: The change in the operation of carriers from single or paired carriers with support vessels to task groups of three or four carriers was a Mistcher idea. He instigated this change for the purpose of concentrating the air groups for a better defense of the carriers.