What sort of reconnaissance was undertaken as the Japanese planned their attack on Pearl harbor? Did they have any intelligence sources on the ground? Did they use any commercial planes or ships to secretly gather intelligence? Was the attack planned for a specific date based on intelligence?
Did the Japanese pilots have a good idea of which ships were in port? Did they know that carriers such as the Enterprise and its task force were not in port?
Did the pilots have any idea of where things would be, or was it a "go that way, blow up ships" situation?
I checked for previous posts on this topic, but didn't see anything similar. Hopefully this is a slightly new angle on questions around Dec 7, 1941. Thanks for any info!
For immediate intelligence, the Japanese employed both submarine and aerial reconnaissance of the Hawaiian islands just prior to the attack. Although the Pacific fleet's routines were well-known to the Japanese, there was a fear that the Americans might have broken their routine and anchored at Lahaina Roads off Maui. The deep waters of Lahaina would have the US fleet to sortie much quicker than the constricted waters of Pearl Harbor. If the Pacific Fleet were there, the plan was to completely rearm the strike force's B5Ns with torpedoes at attack Lahaina.
The submarines I-72 and I-73 reconnoitered Maui on 6 December and reported that, as expected, the Pacific fleet was not present there. Also in keeping with standard IJN doctrine, the cruisers Tone and Chikuma each launched an Aichi E13 floatplane at 0500 7 December to assist the air strike. One of the E13's confirm the submarine's reports of Maui and while the other was to fly over Pearl and provide weather reports for the incoming strike group as well as the type of ships in harbor. The strike group received this information some forty minutes before the attack commenced. However, the importance of this aerial reconnaissance was negligible as the reports arrived too late to be any use for the strike force. The E13 reported no carriers were present, but that did not prevent the Japanese from wasting effort to sink Utah, which the pilots misidentified as a carrier. Although it was somewhat understandable move in the circumstances, the aerial reconnaissance over Maui duplicated the efforts of the submarines and the Japanese had access to much better and timely weather reports by simply listening to American commercial radio. Flying over Pearl risked losing the element of surprise as the radar stations on Oahu did pick up these aircraft at 0645. Had the Army's Air Information Center been active, the radar reports of these aircraft could have triggered an alert. Although the Japanese were unaware of these radar stations, they did not anticipate that these aircraft would be spotted and had no contingency plans in place if these reconnaissance planes alerted US defenses. The aerial reconnaissance was a calculated risk that paid very little dividends, and one that the Japanese attack were very fortunate to get away with.