Hey, thanks for the constructive contribution. Read your post and learned a lot from it. Keep up those informative posts!
The main fleet body was held back by the Japanese so as to not tip their hand in regards to the whereabouts of Kido Butai. That worked; if you look up details of the Hewitt inquiry, it revealed that U.S. intelligence focused on the location of Combined and First Fleets, which to the day before PH were thought to be in Kure, giving no reason to worry. There was a lot of traffic that was picked up heading South, but that certainly wasn't of any concern to PH.
As to BatDiv 1 - they left port before the strike on PH had commenced on December 7 (Hawaii time). Remember that Kido Butai did not communicate with Tokyo, as that would have given away their location. So the Japanese had no knowledge of where Kido Butai was, or what they were up to either. There were, however, contingency plans. This is from hyperwar - good source, recommended read:
http://www.ibiblio.org/hyperwar/AAF/USS ... PTO-2.html
-------------------------------------------
Movement of Pearl Harbor Task Force
In accordance with instructions from CinC Combined Fleet, the Task Force [Kido Butai] sortied from Hitokappu bay at 0600, 26 November and proceeded along the track shown in Appendix 2. On 2 December instructions were received to the effect that negotiations had failed and that 8 December was designated as "X"-day. The refueling was successfully completed on 3 December without mishap. (In the event of failure of the fueling operation it had planned to continue without the destroyers.) After refueling, the Task Force proceeded along the track without incident. No shipping was encountered and the force successfully escaped detection. During the approach, the following instructions were in effect:
If discovered prior to "X"-minus-2-day, the Task Force was to return to Japan without executing the attack.
If discovered prior to "X"-1-day, the decision as to what action to take was the responsibility of the Task Force Commander.
If discovered on "X"-minus-1-day or the morning of "S"-day the Task Force was to continue with the attack.
If at any time during the approach to Pearl Harbor the negotiations with the United States had been successful the attack would have been cancelled.
If, at any time during the approach to Pearl Harbor the American Fleet attempted to intercept the Japanese Task Force, the Japanese planned to counterattack. If the American Fleet advanced into Japanese home waters in pursuit of the Task Force it was planned to commit the Main Body of the Japanese Fleet as a support force.
If, after arriving in Hawaiian waters, it was found that the American Fleet was at sea and not in Pearl Harbor, the Japanese planned to scout a 30-miles radius around Oahu and attack if contact was made; otherwise they were to withdraw..
During the approach the main force in the Inland Sea and land-based air units in the Kyushu area carried on deceptive communications designed to indicate that the Task Force was still in Japanese waters. The Task Force arrived at the launching point 200 miles north of Oahu at 0730, 7 December (Hawaiian time).
-----------------------------------------
They also concluded that:
General Information
The attacks on Pearl Harbor were not continued or followed up by surface craft bombardment because the sole objective of the attack was to destroy the capital ship strength of the United States Pacific Fleet in order to delay any United States advance across the Pacific. Hence,, since this objective was achieved by air attack, no further attack was considered necessary. Also, since the whereabouts of the American carriers was unknown and the chances of locating them by air search were small, it was considered that a quick withdrawal would be most advantageous. Consideration was also given to the probability of a counterattack by the estimated 50 or more large land-based planes that remained in Hawaii after the attack.
No landing operation was planned because insufficient time was available to make all preparations during the month of November and also it was recognized that the problems of ship speed and logistics would have made it impossible to execute the initial attack without detection during the approach.
During the Pearl Harbor Operation the following units were diverted to secondary targets:
The Midway Neutralization Unit (Akebono, Ushio) left Tokyo Bay about 1 December, arriving at Midway during the night of 7 December, bombarded the air base and returned to the western part of the Inland Sea.
It had been planned to conduct an attack on Midway while returning to Japan but the operation was canceled because of weather. On 16 December however, while proceeding to Japan from Pearl Harbor, two aircraft carriers (Soryu and Hiryu), two cruisers (Tone, Chikuma), and two destroyers (Tanikaze, Urakaze) were diverted to Wake Island to assist the invasion on 23 December.
--------------------------------
So, based on that, I would think it likely that BatDiv 1 did engage in a diversionary maneuver. Second possibility, they were already shifted into position for the contingency that the American Fleet was to advance into Japanese home waters in pursuit of Kido Butai.
Cheers.