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Consequences of U.S. Decisions made before Pearl Harbor Attack

Results of Stationing the Fleet at Pearl Harbor


Fleet at Pearl Harbor  approximately one month prior to the attack

The U.S. Fleet stationed at Pearl Harbor approximately one month prior to the Japanese attack. An aircraft carrier is also visible at the top of the row of battleships (left side of Ford Island in this photo). Thees carriers were away during the actual attack. US Navy photo.

The mind set of the US military prior to December 1941, and the resulting decisions, had grave consequences.


By moving the fleet out to Hawaii, it was closer to the Japanese activity, but there was a large negative consequence as well. All of the infrastructure; the highways, the railroads, the ports and the docking facilities, the fuel tanks, the cranes, the repair shops, (all of which were on the west coast) was not adequate on Oahu, because Pearl Harbor was never built for that big of a fleet. In addition, Pearl Harbor, itself, was a very shallow harbor and relatively small compared to, say, the San Francisco Bay. It also had a very narrow neck, so if one major ship sunk in the neck to Pearl Harbor, the whole fleet would be bottled up.


Lack of Sufficient Air Fleet

And it didn't take Admiral Kimmel (the new commander of the Pacific Fleet) very long to realize that the Fleet was in a precarious position. Pearl Harbor was not a good locatation for the entire Fleet and, in particular, there was not a huge air fleet to scout around and protect Oahu. Most the the aircraft in Hawaii and on Oahu were in the hands of the Army. The basic plan called for the army to protect Hawaii and the Fleet, and then the Fleet would sail out with its battleships and aircraft carriers and do battle against the Japanese Fleet.



Kimmel put in a request for an additional 250 Catalinas and he was promised 100 early in 1941. By the end of 1941, the attack came at Pearl Harbor, and none of those 100 aircraft had been delivered. So he had been saddled with about one fifth of the Catalinas that he needed to do standing air patrols.


U.S. Military Strategies Which had Disastrous Consequences

Strategies which lead to disaster included: moving the fleet to Pearl Harbor, aircraft shortages encountered by Admiral Kimmel, General Short's decision to line up the aircraft in rows, and the staunch belief by the U.S. military that the Philippines would be attacked first.



Work on Japanese Naval code

Photo shows work being done on the Japanese Naval code J-25 by Station HYPO in Hawaii. The Japanese order to prepare for war was sent in J-25 prior to the attack on Pearl Harbor, but decoders had been ordered to suspend work on the Naval code and focus efforts on the diplomatic code. Later, enough of J-25 was broken to be used as an advanced warning to the Japanese attack on Midway. NSA photo.

General Short's plan of lining up the aircraft in rows, made them easy targets for the Japanese bombers and dive-bombers. Approximately 328 US planes were lost or damaged without ever having a chance to get in the air. Fires caused by Japanese strafing spread quickly to additional adjacent aircraft. And as for the fleet, twenty-one U.S. ships were sunk or damaged during the Japanese attack, including the sinking of five of the eight battleships that were present.



Delivery of the Declaration
of War to Pearl Harbor

On December 7, 1941, the army radio in Washington D.C. was experiencing atmospheric interference, and Joint Chief of staff, Army General Marshall, declined to use the navy radio network to send the message to Pearl Harbor that the Japanese had declared war.


So the message that the War Department actually sent to Hawaii on Sunday morning went by Western Union telegram and arrived an hour and a half after the attack was over.

Periodically the Japanese would change their Naval codes and there was a change before the attack on Pearl Harbor. Very little work, if any, had been done to decode the new JN-25 code because work was focused on the diplomatic code. Deciphering of the diplomatic code was going well, and the results allowed the State Department to read instructions that were going to the Japanese diplomats in Washington D.C., even before the Japanese diplomats could get them fully decoded.


That strategy fell apart because the Japanese Navy sent out attack preparation orders in the Naval JN-25 code, which the Americans had stopped decoding. Although U.S. personnel was making copies of the JN-25 coded messages and filing them, these were not decoded until after the war.

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Eventually in 1946 and 1947, those Japanese Naval messages were decoded. At that point it became apparent that had they been decoded in 1941, when they were received, the United States would have intercepted orders to the Japanese fleet to prepare for the attack on Hawaii. At that point the U.S. would have had several days of advance notice of the attack.


This was perceived as very embarrassing information by the U.S. Navy in 1947, and so these transcripts were classified as top secret at that time and were not released for over forty years.


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