And of course, the fighter should really have been called the "00" but they dropped one "0" and called it the Zero (Japanese designation). That designation caught on, and Americans almost always called it the "Zero", even though the official Allied code name was the "Zeke".) The actual Japanese designation was A6Mx, with the x being a number indicating a change. Minor changes were indicated by an additional "model" number. Major changes to the basic type were designated by a letter. The Zeros used at Pearl Harbor were designated as A6M2 Model 21.