Predicting Pearl Harbor 

Much has been made about the Japanese raid on Pearl Harbor on December 7, 1941, 80 years ago. Many authors and historians have asked, and are still asking, what (if anything) could have been done to avoid the outcome, and whether there were any warning signs that were misinterpreted or ignored. In fact, our own recent article on the history of military wargames (Read our earlier article – Wargames) mentioned that the scenario of a potential attack on Pearl Harbor had been, in fact, explored by the U.S. Naval War College several times between the two World Wars. Today, we'll take a look at four people who have either demonstrated or at least prognosticated Pearl Harbor's vulnerability and who were ignored at the time.
 
The first whistleblower was no smaller person than Billy Mitchell, often called the father of the U.S. Air Force. Mitchell enlisted in the U.S. Army as a private in 1898, and spent his early career with the Signal Corps in the Philippines and Alaska. He visited several battlefields of the Russo-Japanese War of 1904-1905, and became convinced that a future war between America and Japan was inevitable. In 1916, he acted as temporary head of the Aviation Section of the U.S. Signal Corps, the organization that would eventually evolve into the United States Air Force. When America joined World War I in 1917, Mitchell became the first American officer to fly above German lines in Europe (though to be fair, he was only a passenger and the plane was flown by a French pilot). In 1918, he led close to 1,500 British, French and Italian planes in the Battle of Saint-Mihiel, in one of the first combined air-ground offensives in history.  He became a loud, determined and popular proponent of air force development after the war.

Mitchell was far ahead of most of his contemporaries, and many of his ideas ran into strong opposition by more conservative military and political decision makers. He foresaw the ability of aircraft to sink battleships, as well as the need to have an Air Force which is independent of both the Army and the Navy. He advocated the development of such technologies as bomb sights and aerial torpedoes. He was also a pioneer in patrolling borders and fighting forest fires from the air.
 
Forced to fight for his ideas every step of the way, Mitchell became a skilled public figure, who had a talent to attract and win over media and public attention. In 1924, his superior, Major General Mason Patrick, sent Mitchell on an inspection tour of Hawaii and Asia in an attempt to get him and his pesky reform arguments out of the limelight for a while. Mitchell returned with a 324-page report. In this report, he predicted that Japan will attack the United States sometime in the future, and that the attack will involve an aerial raid on Pearl Harbor. He also foresaw, correctly, that the goal of the raid would be to cripple the U.S. fleet there and keep it in place while Japan invaded the Philippines (which is exactly what Japan did in 1941). He guessed that Japan would attack a 7:30 a.m., a forecast that was uncannily close to the actual time of the attack, 7:55 a.m. Mitchell did get one important detail wrong. Even he couldn't foresee the ability of a carrier-based fleet to launch a heavy aerial force, and thus he assumed the Japanese attack would come from Japanese-held islands in the Pacific.

The report was ignored by the government and the military…with one notable exception. A government official went on record saying "Should there be such a war, America would have to fight it a long way from home...It would be gravely embarrassing to the American people if the ideas of your General Mitchell were more appreciated in Japan than in the United States," also adding "Our people will cheer your great Mitchell and, you may be sure, will study his experiments." The only problem was that even this acknowledgment didn't come from an American politician, but from a member of the Japanese Parliament, who witnessed one of Mitchell's demonstrations of anti-naval air power as a foreign observer.

Another warning came in 1932. Between the two World Wars, the Navy and the Army held not only numerous wargames to develop tactics and strategy for a future war, but also exercises involving actual soldiers and ships playing out mock battles. Fleet Problems were a series of naval exercises, and Army-Navy Grand Joint Exercises ("GJEs") were organized jointly by the two branches. One recurring situation in these exercises was a hypothetical conflict between the U.S. and a "militaristic, Asian, island nation" – which clearly meant Japan. GJE4 in early 1932 focused on a scenario involving Hawaii and Pearl Harbor. In this exercise, Black side (meaning the enemy, while the U.S. was Blue) invaded and captured Pearl Harbor, and an American fleet steamed from San Diego (which was the main Pacific naval base at the time) to retake it. The expectation, based on American doctrine at the time, was that Blue fleet would only use its two carriers, the USS Lexington and the Saratoga, for aerial scouting. The approaching fleet would be spotted by Black, who would depart from Pearl Harbor for a decisive naval battle in the open seas.

What happened defied expectations. Admiral Richard Leigh, the commander of Blue fleet, did not send his entire force as one group. Instead, he gave the two carriers and a destroyer escort to Rear Admiral Harry Yarnell, and had him head for Hawaii on his own, ahead of the rest of the fleet. And Yarnell did exactly what the Japanese would do 9 years later. He had his ships maintain radio silence and sail on a route away from shipping lanes to avoid chance meetings. Using the Pacific winter storms as a shield against Hawaiian radar, he approached the island of Oahu undetected from the north-northeast and launched an air strike with 152 planes from the two carriers, attacking on Sunday (just like the Japanese would in 1941), when most sailors were off duty.

Yarnell's planes dropped flares and flour bags to simulate bombing runs. They first "destroyed" all of the Black aircraft on the ground, before they could take off from Oahu's multiple airfields. Then they concentrated on Battleship Row, causing significant damage and preparing the way for an amphibious landing once the main fleet arrived. At the time, the umpires for the exercise declared it a complete victory for Blue. The President of the Naval War College, who was there as an umpire, specifically noted the mobility of the carriers, and how it gave the attackers initiative over land-based air power.

The War Department later changed the ruling, arguing that Yarnell "cheated" by attacking on Sunday and from an irregular direction, and that in a real war the carrier force would have been spotted and destroyed in time. They also claimed that an Asian attacker could never have displayed the same accuracy against the anchored warships, since "everyone knew that Asians lacked sufficient hand-eye coordination to engage in that kind of precision bombing." It should be noted that American attitudes towards Asians in general and the Japanese in particular were rather ignorant and racist at the time. It was widely accepted that the Japanese were technologically inept and poor aviators since their "eyes were not right," and because their inner ears and sense of balance were askew from having been bounced around on the backs of their big sisters as babies.

As it is standard with military exercises, GJE4 was heavily studied and analyzed, numerous conclusions were drawn and arguments had. Lessons included the realization that 2 carriers in the Pacific were not enough, and another 4-6 were needed; also, that heavy cruisers couldn't properly service sea planes, as they rolled too much from wave action. Amid these and other genuinely useful lessons, there was one that the Navy failed to give enough attention to: Pearl Harbor could be successfully bombed by a carrier-based air force.
 
The U.S Navy failed to address Pearl Harbor's vulnerability to an air attack, but another organization was much more diligent: the Imperial Japanese Navy. Four years after GJE4, the exercise was included in the curriculum of the Japanese Imperial Naval Academy, and the final exam that year included the question "How would you carry out a surprise attack on Pearl Harbor?"

The third warning was issued by someone associated neither with the Navy nor the Army Air Corps, but rather the Army proper: then-Colonel George S. Patton. Serving as the intelligence officer of the Hawaiian Division in 1937, he wrote a report simply titled Surprise. In this paper, he noted the following:
 

• The best way to capture Hawaii was by complete surprise.
• Some Japanese-controlled islands were only 2,500 miles away from Pearl Harbor and a force steaming from there would be traveling through lonely seas, with a low chance of being spotted.
• Japan had always attacked without declaring war since it modernized.
• Air and submarine forces on Oahu would need to be neutralized before capturing the island.

 
Based on these observations and Japan's strategic needs, Patton surmised that Japan would most likely attack Pearl Harbor by surprise in an attempt to knock out American forces quickly.

A fourth and final warning came in 1938, with another exercise that was similar to GJE4 in several ways. This time, the carrier force was commanded by then-Vice Admiral Ernest King, who had significant experience with naval aviation. One difference from the 1932 exercise was that this time, King's carrier force was actually on the mock-Japanese side, attacking, rather than liberating, Pearl Harbor. His actions, however, still corroborated Yarnell's findings. He sailed close to Hawaii, successfully bombed the airfields on Oahu, then recovered his planes in time to beat back a counterattack of PBY Catalina flying boats. And, again, Pearl Harbor's vulnerability was not studied in sufficient detail.

The question of Pearl Harbor will not be settled permanently for a long time – if ever. Questions of mistakes, oversights and misunderstandings will continue to captivate public opinion. But one thing cannot be disputed: the base's vulnerability to an air raid could have been, and perhaps should have been, recognized 16 years before the Day of Infamy. The warning was there, only the decision makers didn't know where to look and who to listen to.