Both, although the US Navy was doing a very poor job of it with their aircraft. The US Army airpower was responsible out to some 20 miles offshore, the US Navy was supposed to be covering out to 700 miles. Although Kimmel never informed Short that the US Navy wasn't doing its job. Kimmel never asked for US Army aircraft to help out, and Kimmel never asked for Short to keep the radar stations manned 24/7. While Tom Kimmel would have us believe that Washington was not giving Admiral Kimmel all the facts, he never once mentions all the information Kimmel was withholding from Short. Yes, both Richardson and Kimmel considered using anti-torpedo netting. However, they both figured it would do more harm than good, considering the crowded harbor and how the netting hampered ship movement within. Silly does not even begin to describe the Americans belief in their superiority. Think along the lines of inconcieveable or unfathomable. I don't think it was studied in great detail. While the attack may have seemed impressive, The Med is a swimming hole compared to the Pacific. At the time the Americans did not know that the Japanese were capable of underway refueling, even still the Soryu, Hiryu, Tone, and Chikuma all carried many fuel oil barrels stashed any place extra space could be found to help improve their ranges. So, right there is one strike against the Japanese attacking. Another strike is American racism against the Japanese in that they thought Japan could never conceive of such a plan, let alone carry it out. A third strike is the American overestimation of their own defences, and that such a raid would surely be detected well before it got within striking range of the Hawaiian islands, and when detected American forces would surely destroy it. Oh, let's not for get the Japanese invasion force, that was under US and British observation, moving towards Malaya. This focused US attention there and not closer to home, this was the long held American belief was that the blow would fall on the Philippines, Guam, Wake, etc.