Japan's attack on Pearl Harbor was driven by compelling strategic logic that was well-known for many years to naval planners in both Japan and the US. Unless the US Pacific fleet was taken out at the outset of the war, it would endanger Japan's conquest of East Asia, perhaps even denying Japan the vital oil fields of the Dutch East Indies.
Long before the vulnerability warned of in Exhibit 40, a Japanese carrier attack on Pearl Harbor was anticipated as a distinct possibility. In the late 1920s, war games at the Japanese Navy War College examined a carrier attack against Pearl Harbor. In 1929, then Captain Yamamoto lectured on the topic.
Of particular interest for our purposes, in 1932, widely-publicized US Pacific Fleet war exercises included a surprise carrier attack on Pearl Harbor carried out by Admiral Harry Yarnell -- on a Sunday morning no less. Prefiguring Japan's methods, in sailing from anchorages in California, Yarnell used radio silence, avoided shipping lanes and radar coverage, and had minimal escorts for his carrier striking force.
Not only was Washington well aware of Pearl Harbor's vulnerability to aerial attack, but so were the responsible naval officers on scene. Famously, on Dec. 2, 1941, Lt. Cmdr. Edwin T. Layton, the Pacific Fleet's intelligence officer, briefed Adm. Husband E. Kimmel, the Pacific Fleet commander, and presented a summary showing the approximate position of Japanese fleet units based on radio traffic.
Kimmel noted that there was no trace of either of the Imperial Navy's two carrier divisions. "You don't know where the carriers are?" "No, sir," replied Layton. "That's why I have 'Homeland waters' with a question mark. I don't know."
"You mean they could be coming around Diamond Head and you wouldn't know it?" The best reply that Layton could muster was that "I hope they would be sighted before now."
Was the Japanese attack on Pearl unexpected and improbable? Not really.
Admiral Yarnell conducted a raid, but not a strategic attack. The author in the article says, “For the first time in history, there existed a carrier force comprising enough aircraft to do strategically meaningful things on the battlefield. Instead of just scouting, Kido Butai had the ability to attack enemy fleets—and enemy fleet bases.” He did and I need to do a better job of emphasizing the magnitude of the Japanese accomplishment.
When I looked up Admiral Yarnell on the Internet I found the below comment indicating his dramatic demonstration did not have the impact it could have had although defenses at Pearl were much more formidable than in 1932.
“Ironically, in the U.S., the battleship admirals voted down a reassessment of naval tactics. The umpire's report did not even mention the stunning success of Yarnell’s exercise. Instead they wrote, ‘It is doubtful if air attacks can be launched against Oahu in the face of strong defensive aviation without subjecting the attacking carriers to the danger of material damage and consequent great losses in the attack air force.’”
He could have been legitimately rebutted for emptying the decks of every operational aircraft for the attack. He should have left at least half of both fighter squadrons behind to defend the task forces.
Enticing the U.S. Navy into a sea battle in the Western Pacific was Japan’s best option. Japanese ships of short operational range would not be at a disadvantage. Japan could use land based reconnaissance and attack aircraft in battles as we attempted to counter their attacks against Guam and the Philippines. Ships lost at sea could not be recovered as they could if they were hit in harbor. But Japan’s Naval General Staff lost the arguments.
That statement by Layton relates to his last briefing of Kimmel and makes the point of just how indecisive it had to be when it was only based on traffic analysis. Naval traffic analysis in Hawaii had detected a message flurry followed by radio silence as they had observed for tactical operations in February and July when major units had remained in port. In context he talks about what is possible after telling Kimmel what is probable.