They chose to use bombers because thier primary objective was to destroy as many ships as possible. They did have one squadron of fighter planes in each wave, however. The reason they did this was because Yamamoto predicted that the troops at Pearl Harbor would be able to a launch a few planes. There were two waves of planes. The first wave of planes were to destroy as many capital ships as possible.
Capital ships are ships that are powerful.
The planes that were still up and running after the first wave were to join in the second wave. The second wave of planes were to destroy whatever was left after the first wave of planes finished thier mission. These were mostly carrier ships and submarines that were surfaced. During this attack exactly ten major command ships were destroyed. Some of the ships that were destroyed were the U.S.S. Arizona, the Pennsylvania, the Maryland, and the West Virginia.