Pearl Harbor planning involved hundreds of staff officers at different levels of the Japanese navy. The Naval General Staff and Combined Fleet both contributed teams and senior officers. Such broad involvement need not make secrecy impossible if studying war with the United States was already routine work. A smaller group preparing a live operation could then remain concealed within that larger activity. This is one reason for inferring a continuing planning effort before the specific 1941 operation.
Chapter · 23:48-25:40
How routine staff work could conceal Pearl Harbor preparations
Routine studies of war with the United States could conceal the smaller group preparing a live attack within a broad staff network.