Simplify the following text for a Grade 8 native English-speaking person.
Original: The attack on Pearl Harbor ( called Hawaii Operation or Operation AI by the Japanese Imperial General Headquarters ( Operation Z in planning ) and the Battle of Pearl Harbor ) was a surprise military strike conducted by the Imperial Japanese Navy against the United States naval base at Pearl Harbor , Hawaii , on the morning of December 7 , 1941 ( December 8 in Japan ) .
Simplified: The Attack on Pearl Harbor was a surprise attack by Japan against the United States naval base at Pearl Harbor , Hawaii on the morning of December 7 , 1941 .