On the day the bombs fell on Pearl Harbor, the U.S. Navy, or at least a tiny segment of it, had had the Imperial Japanese Navy under attack for about twenty years. The attack was, of course, a silent one, of which the Japanese were totally unaware.
Whitlock, Duane L.
"The Silent War against the Japanese Navy,"
Naval War College Review: Vol. 48
, Article 6.
Available at: http://digital-commons.usnwc.edu/nwc-review/vol48/iss4/6