Complex sentence: The Imperial Fleet, under Admiral Isoroku Yamamoto, knew that they would meet resistance, and intended to draw whatever was left of the American fleet into a battle wherein any remaining U.S. naval warships could be destroyed.
Split into simpler sentences: The Imperial Fleet, under Admiral Isoroku Yamamoto, knew that it would meet resistance. The intention was to draw whatever was left of the American fleet into a battle wherein any remaining U.S. naval warships could be destroyed.