Japan's merchant-fleet recall signaled imminent war

How much warning did Japan's October 1941 recall of its merchant fleet provide?

It was a major warning that Japan would move, but it did not resolve whether the attack would go north or south.

Recalling a worldwide merchant fleet was a major mobilization indicator because shipping was essential to any Japanese campaign. Allied observers recognized that a large operation was coming. The unresolved intelligence problem was direction: Japan could move north against the Soviet Union or south toward Southeast Asian resources and Western possessions. Strategic warning was therefore genuine but still too broad to identify Pearl Harbor as the decisive opening target.