Posts Tagged ‘Midway Island’

On March 13, 1942, U.S. cryptanalysts wedged the first cracks into Japan’s JN-25 code system.  As we well know, this bright spot falls into that dark, 6-month period for the U.S. armed forces between the disaster at Pearl Harbor and its first victory at Midway.

The advent of radio had really transformed radio communications for the world’s navies, allowing messages to be sent instantly over long distances.  Unfortunately, anyone with a receiver and the proper frequency could hear the message, and if one knew the language, well…secrets didn’t stay secrets very long.  So out came the codes, and they increased in complexity rapidly as each previous version was cracked by the enemy.

During World War II, Japan used numerous different coding systems.  There was one for the army, a Flag Officers Code (that the U.S. never cracked), and numerous others.  But JN-25 (as it was called by the U.S.) was the biggie, as it was used by the Japanese Navy…hence the “JN”.

This system consisted of a codebook with nearly 30,000 entries.  On top of that book was a “superenciphering” 300-page additive book, with each page containing 100 random five-digit sequences.  This created a sort of two-tiered encryption, which proved to be a tough nut to crack, indeed…even with the use of a very rudimentary computer (the IBM ECM Mark III).

But U.S. cryptanalysts were aided in their jobs by the Japanese themselves.  First, the five-digit sequences in the additive book were not used just once, but repeatedly, which gave codebreakers a hook on which to grab.  Second, Japanese command formality meant that phrases like “I have the honor to inform your Excellency” were used many times, as were nicknames for various commanders.  This repetition is anathema to encryption, because repeated patterns are the first things for which codebreakers look, and even using a different five-digit superencryption key couldn’t hide those pattern phrases for very long.

So rather that having to decipher a massive code system, it really became an exercise in collecting enough Japanese messages and putting enough smart people to work finding those repeated patterns.  Add in two parts patience and two parts persistence, and stir until enough of JN-25 was cracked to begin reading messages.

Within a month, the U.S. Navy had enough information to try a little test.  “Island AF” kept coming up in messages and the Navy suspected it was a reference to Midway.  So they told the guys on Midway to transmit that they were low on water.  Sure enough, a coded Japanese message was intercepted days later reporting Island AF low on water.

Game over.  Check and mate.

The Japanese knew their systems could be hacked, so they changed them periodically.  But their initial arrogance (caused by their incredible successes) meant they didn’t change them as much as they should have.  And they never really altered the basic structure of their messaging.  So U.S. codebreakers would simply look for the phrases and nicknames, which largely gave them “the key to the candy store.


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The Battle of the Coral Sea, fought in early May of 1942, ended with one U.S. carrier (the USS Lexington) permanently water-logged and the USS Yorktown wounded.  She had managed to steer clear of nearly all her attackers, but one was able to hit her with a bomb that caused heavy damage below decks.

Experts estimated that the Yorktown would require several months of repair time.  Unfortunately, the U.S. Navy didn’t have several months…it didn’t even have one month.  Every available ship was needed for the inevitable encounter coming at (or around) Midway.  The Japanese were heading there with a staggering array of firepower, and the U.S. had to respond, or risk losing not only Midway, but Pearl Harbor and the Hawaiian Islands as well.

There were only three carriers available to the Navy in the Pacific, one of which, the Yorktown, now wasn’t able to launch or land planes.  The other two, Hornet and Enterprise, had already departed for Midway when the Yorktown arrived at Pearl on May 27th.  Three months of work had to be completed in a lot less time than three months.

Repair crews set to it.  Working night and day for three days, hundreds and hundreds of men made the ship “plane-worthy” again.  There was no way to get the ship back to good-as-new condition, but they completed enough of the repairs required to conduct air operations.

At the last possible moment, with the torches still glowing and sparks still flying, the Yorktown set sail on May 30, 1942.  Thought by the Japanese to have been sunk in the Coral Sea, the Yorktown would help provide quite a surprise for the Japanese just a few days later.

Recommended Reading: Miracle at Midway

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The Japanese Navy in May of 1942 was still largely unbloodied.  And it was not because they had simply avoided battle.  Rather, they had pretty much stomped any enemy that had dared oppose them.  Even the “setback” in the Coral Sea couldn’t really be looked on as a defeat.  After all, while the Japanese had lost a carrier and some airplanes, they were still the overwhelming power in the Pacific.  And the Americans had lost the USS Lexington, leaving them with just three aircraft carriers (a fourth, the USS Saratoga, had just finished repairs but was in San Diego being re-outfitted).

And now the focus was on Island AF.  You wondering where that is?  Island AF is actually Midway Island in Japanese code-speak.  The Japanese used an assortment of coding systems for their various organizations, but JN-25 was the one used by the Imperial Japanese Navy.  It was the most important and also the most secure of all Japanese ciphers.  And therefore, it was the biggest target of U.S. codebreakers.

And U.S. codebreakers had cracked much of it.  In fact, “Island AF” was part of the U.S. scheme as well.  The messages deciphered by U.S. intelligence mentioned “Island AF” on numerous occasions, and it was suspected the reference was to Midway.  So the U.S. Navy phoned the guys on Midway and told them to send an uncoded message back stating they were low on fresh water.  It was done and, not long after, the U.S. intercepted and deciphered a Japanese message about “Island AF” being short of water.  The U.S. had their answer.  From this they learned that Midway was the subject of intense Japanese interest.

But the Japanese were also aware that their codes could be compromised, so they periodically changed them.  They had done so in the weeks leading up to attack on Pearl Harbor, which greatly assisted in the success of that operation.  And now, six months had passed and another major operation (Midway) was looming.  It was time for another change.

But it’s possible that Japanese success over the first half of 1942 bred a little over-confidence in the Navy.  On May 25, 1942, the Japanese significantly changed their JN-25 coding structure and ciphers, which meant U.S. codebreakers had to start their jobs all over again.  But the change occurred right after they had broadcast their full operating plan for the attacks on Midway.  And so the plans (or at least parts of it) fell right into the hands of the U.S. Navy.

For the Japanese, the change from JN-25b to JN-25c meant they would achieve surprise when they occupied Guadalcanal in July of 1942.  But their attempt to take Midway would end in disaster.

Recommended Reading: Incredible Victory – The Battle of Midway

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In the early hours of  May 5, 1942, things were still looking pretty good for the Japanese military.  New conquests included the Dutch East Indies, Malaysia, Singapore, and the northern coasts of New Guinea.  The Philippines was largely occupied as well, and Joe Stilwell and his men were packing their bags in Burma.  The Imperial Japanese Navy enjoyed success wherever it fought.

Yeah, there were occasional setbacks.  The invasion of Port Moresby had been delayed for a couple months.  Corregidor was proving a tougher nut to crack than originally estimated.  And there were those bombers that made a bit of noise over Tokyo in mid-April.  But Doolittle’s raiders did little more than scare the populace and, frankly, Japanese forces had broken down Corregidor’s defenses to the point that Homma’s troops were planning a landing and occupation…tonight.  So all was looking pretty good.

It was time for phase two of operations.  Those included pushing Australia and India out of the war as well as diminishing the U.S. Navy’s presence in the Pacific.  So Port Moresby was back on the table and, in fact, on this glorious May 5th morning, an invasion fleet was heading there now.

Also on the map was Midway Island.  The atoll was small, basically big enough for an airstrip, a few guns, and some fuel tanks.  But after the Japanese victory at Pearl Harbor, the U.S. Pacific fleet was a mess.  Commander-in-Chief Isoroku Yamamoto believed that occupying Midway would give them a base of operations from which they could actually expel the U.S. Navy from Pearl Harbor, thereby taking control of the Pacific.

So he and his staff created an intricate plan that would draw the remnants of the U.S. fleet into a killing field of Japanese firepower.  A decoy force would head towards Alaska with another force headed towards Midway.  When the fleet responded to that second force, a third (and more powerful) fleet would swoop in and deal the killing blow.  Yamamoto polished up the ideas and sent them to his superiors…and waited.

And it was on this morning, May 5, when Corregidor was falling, and Port Moresby was as good as occupied, and everything was going right, that Imperial General Headquarters issued “Navy Order No. 18”.  It ordered Admiral Yamamoto to carry out his plan to occupy Midway Island and the western Aleutians with help from the Army.

“Navy Order No. 18” turned out to be one of the most pivotal orders of war, but not for the Japanese Navy.

Recommended Reading: Miracle at Midway

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Once again, I’m writing a day late and “back-publishing”…I really dislike doing that.  But the cable modem at home refuses to connect to the wondrous Internet cloud and, last night, clouds of a tornadic variety had us watching the weather and scurrying to the basement.  All of which served to make this piece “late to press”…my apologies.  I think a new cable modem will address the connection problems.  As for the weather, well…

As the sun rose on the morning of June 5, 1942, Japanese naval commanders faced a pretty bleak dawn.  The Battle of Midway was quickly becoming an unmitigated disaster.  The previous day’s action had resulted in two Japanese carriers sunk (Kaga & Soryu) and another two burning and dead in the water (Akagi & Hiryu), both of which would slip below the morning waves.  But as badly as it had gone, there was still some reason for optimism.

Yamamoto’s airborne charges had located and attacked the USS Yorktown and put her out of the fight.  Though still afloat, she was down by the bow and listing badly.  Furthermore, the Japanese Admiral still held a huge numerical advantage in firepower, though without any flattops, he was precariously exposed.  He had decided to cancel the Midway invasion, but to salvage some pride, he ordered a bombardment of the atoll.

The destroyer and cruiser divisions closest to the island were given their orders and off they went.  As they approached Midway, a U.S. submarine was spotted.  When the report was flashed to Yamamoto, he suddenly called off the bombardment and ordered the ships to return…which led to the next debacle.  In the midst of the change of direction, the heavy cruisers Mogami and Mikuma collided, causing damage to both.

In the meantime, the Japanese sub I-168 had been hard at work, closing very slowly and cautiously on the disabled Yorktown.  Her crews had worked feverishly and kept her afloat and the decision was made to tow her back to Pearl for repairs.  Being towed by the destroyer USS Hammann, they both made easy targets for sub, who dispatched both to the ocean floor with torpedoes…the Hammann going down in minutes, the Yorktown surviving until the next morning.

And that was, for all intents and purposes, the Battle of Midway.  U.S. pilots, seeking revenge for the loss of the Yorktown, would find Yamamoto’s damaged cruisers the next day, sinking the Mikuma and damaging the Mogami (shown above) to the point of sitting out the War for more than a year for repairs.  The Japanese fleet turned tail and made for friendlier waters, and never came close to Midway again.  And true to form, on the 9th, Tokyo radio would cheer the astounding Japanese victory at Midway.

Recommended Reading: Miracle at Midway

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The Foreward to Walter Lord’s Incredible Victory begins as follows: “By any ordinary standard, they were hopelessly outclassed.  They had no battleships, the enemy eleven.  They had eight cruisers, the enemy twenty-three.  They had three carriers (one of them crippled); the enemy had eight. Their shore defenses included guns from the turn of the century.  They knew little of war.  None of the Navy pilots on one of their carriers had ever been in combat.  Nor had any of the Army fliers.  Of the Marines, 17 of 21 new pilots were just out of flight school-some with less than four hours flying time since then.  The enemy was brilliant, experienced and all-conquering.

Such was The Battle of Midway…on paper.  A total mismatch.  A slaughter waiting to happen.  On the Japanese side, nearly 190 ships.  On the American side, less than one-third that number.  It’s a good thing the Battle of Midway wasn’t fought on paper, because any rational analysis would have painted a bleak picture for the U.S. Navy.

But what started on the morning of June 4, 1942 as a day of destiny for the Japanese ended as a day of disaster.  In the space of six minutes (10:22-10:28am), U.S. Navy dive bombers had hit three carriers (Akagi, Kaga, & Soryu) and rendered them floating wrecks.  A fourth carrier (Hiryu) would be added to that list later in the afternoon.

This most improbable of American victories didn’t stem from one factor, but from many, all of which conspired to make the impossible a reality.  Among them, Admiral Nagumo not being notified of the cancellation of Operation K, so he wasn’t aware of the U.S. fleet’s presence.  A group of Japanese picket subs that arrived late to their scouting station, where the U.S. fleet had passed just a day before.  The catapult that malfunctioned, causing a Japanese float plane to launch 30 minutes late…the same float plane that would discover the U.S. fleet, and then require another 45 minutes to identify a carrier as one of the vessels.

And how about Admiral Spruance’s decision to send in two low-level torpedo squadrons (Torp Squadrons 6 & 8) with no fighter escort?  Flying at extremely slow speed, they presented a juicy target to the Japanese fighters protecting the carriers, who swooped down and shredded them.  And then, just minutes later, those same Japanese pilots watched helplessly, at low altitude with low fuel and little or no ammo in their guns, as U.S. dive bombers swooped down and chopped three Japanese carriers to pieces.

Or Nagumo’s decision to land his planes returning from their attack on Midway Island and then rearm them for carrier attacks, which left his carrier decks awash in aviation fuel and bombs?  Or the bravery of those afore-mentioned Torpedo Squadron pilots, who flew into what they knew would be a slaughter, but did it anyways?

There were other factors as well, but suffice to say that the Six-Minute Miracle at Midway (and the 5-6 hours that led up to it) is simply one of the most astounding turn of events in the history of warfare.  In six minutes (about the time it took you to read Today’s History Lesson), the vaunted Japanese military went from unbeaten and largely unbloodied to a force that would never recover the initiative again.

Recommended Reading: Incredible Victory – The Battle of Midway

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