It is difficult to research this question due to conspiracy theories.
When I was in the Navy on submarines, we used to get daily reports on the order of battle for major ships of foreign militaries (mostly China) in the Pacific. That daily report would often show submarines, cruisers, etc... and where they were, including whether or not they were in port.
Looking back towards WW2, I know naval intelligence was nowhere near what it is today, but how in the world did that group of Japanese ships manage to transit the entire Pacific under the noses of the US Navy?
The reason I ask is that the popular conspiracy myth that they "knew" and "allowed" the attack to happen absurdly assumes that the supposed reports of Japanese ships the day before the attack on Pearl Harbor were ignored, or at best, taken as a nonissue.
Taking into account Japan's hostile actions in China prior to the attack on Pearl Harbor, it seems to me that the movements of their fleet would be something high on the list of naval intelligence collection requirements at the time.
If the Japanese group of ships were traveling at 20 knots and covering the ~3,850 miles from Japan to Hawaii, it would take 6.97 days to complete the transit. Assuming that after 2 days of transit, plotting the course of the Japanese group would point towards Hawaii fairly clearly. That would leave 4 days. I understand that in terms of war time frames, 4 days is very short, but it is still surprising to me that they were able to transit all the way to Hawaii undetected.
Am I missing something here? It just seems that the movement of a naval force by a country at war, Japan, would have been of great interest.
The Kido Butai was Radio Silent with stations at major fleet bases in Japan using the call signs of the units involved, essentially were portrayed to either be in port or training in the Sea of Japan. The seamanship required for the transit is actually very impressive, as the fleet then had to meet with their oilers to refuel halfway there in the middle of the North Pacific and had to do so without radio usage.
And at that point USN SIGINT was just starting to get a grip on the Japanese naval codes, and one of the first things fixed were the ship/squadron/admiral identifiers, so you can then triangulate where the source is.
But once the ships set sail the vast majority of traffic just STOPPED. The level of traffic was incredibly reduced, and Kimmel was told of it by his staff, but frankly the more likely targets to everyone were the Philippines, or points South, not 2/3 of the way across the Pacific. Though this Quote is very perceptive by Kimmel:
“Do you mean to say,” Kimmel asked Layton on December 2, “they could be rounding Diamond Head [an Oahu landmark] and you wouldn’t know it?”
“I hope they would have been spotted before now,” Layton said.
Then as you can see on the map below the track took them WELL outside scouting range into the most barren open expanse of water on earth in the North Pacific.
https://upload.wikimedia.org/wikipedia/commons/0/05/PearlHarborCarrierChart.jpg
http://www.nationalgeographic.com/pearlharbor/ngbeyond/stories/story4.html
