Actually they had extensive prior knowledge about the coming attack on Pearl Harbour - I started writing a paper on false flags and actually found out there has never been a single war in the last 120 years that was not started without a pretext of some form - albeit even a inverted false flag.http://www.soest.hawaii.edu/HURL/midget.html
This midget sub find has been described as the most significant modern marine archeological find ever in the Pacific, second only to the finding of the Titanic in the Atlantic. The Japanese midget sub was one of five attached to five I-class mother submarines and brought from Japan to be launched 5-6 hours before the aerial attack, within a few miles of Pearl Harbor. Each had a crew of two. The subs were battery powered , 78 feet long , 6 feet in diameter and weighed 46 tons. They carried two torpedoes and a scuttling charge to avoid capture. Although experimental in design, they were very advanced for the time. For short periods, they could run at 20 knots. These midget submarines were completed only months before the attack allowing little time for the crews to train. All of the five submarines comprising the advanced attack force were sunk or captured. The type A midget submarines had a series of basic design problems including trim and ballast control and problems both with battery life and battery monitoring. Later redesign, as five man midget submarines of the Koryu class, addressed but did not solve these problems. The Japanese midget submarines although believed at the time to be a potent secret weapon, in actual fact, were never highly effective. So far four of the five original midget submarines attacking Pearl Harbor have been found.
WHY DO WE CARE - Because these submarines engaged Naval forces hours before the planes hit. The 'excuse' that naval high command gave is that the USS Ward was operated by a bunch of reserve members, and they were just chasing 'ghosts' and there was no need to alert the crew.http://www.history.navy.mil/photos/sh-fornv/japan/japtp-ss/mdg-a-2.htm
Agents were warned 11 days prior: http://www.oldthinkernews.com/Articles/oldthinker%20news/1945_homeward_bound_army_newsletter.htm
1982 Book 'Infamy: Pearl Harbor and Its Aftermath" Pulitzer-prize winner John Toland reveals that almost everything the Japanese were planning to do "was known to the United States" on the morning of the attack, via intercepted messages never communicated to commanders at Pearl Harbor. He cites the case of US counterintelligence translator Dorothy Edgers who uncovered critical Japanese messages days before the assault, including "a scheme of signals regarding the movement and exact position of warships and carriers in Pearl Harbor." But Edgers' boss, Alwin Kramer, seemed "more annoyed than electrified" at the discovery and ordered her to "run along home." Unbeknownst to Edgers, Kramer was part of the subterfuge.
Its endless, it all pops up when you google 'Pearl Harbor Prior Knowledge.'