Simplify the following text for a Grade 6 native English-speaking person.
Original: Michener 's writing career began during World War II , when as a lieutenant in the U.S. Navy , he was assigned to the South Pacific Ocean as a naval historian ; he later turned his notes and impressions into Tales of the South Pacific , his first book , published when he was 40 and the basis for the Broadway and film musical South Pacific by Rodgers and Hammerstein .
Simplified: He was assigned to the South Pacific Ocean as a naval historian . He used his time there as the basis for Tales of the South Pacific , his first book .