After the Japanese attack on Pearl Harbor, Navy cryptographers, with assistance from both British cryptographers at the Far East Combined Bureau (in Hong Kong, later Singapore, later Ceylon), and Dutch cryptographers (in the Dutch East Indies), combined to break enough JN-25 traffic to provide useful intelligence reports and assessments regarding Japanese force disposition and intentions in early 1942. Rochefort would often go for days without emerging from his bunker, where he and his staff spent 12 hours a day, or even longer, working to decode Japanese radio traffic. He often wore slippers and a bathrobe with his khaki uniform and sometimes went days without bathing.
While Joe Rochefort and his team were busy tracking the enemy’s advance toward Australia from decrypted fragments, he also began detecting Yamamoto’s Midway-Aleutians operation. Of special help was a decrypt of April 29 referring to the dispatch of maps of the Aleutian Islands. Another signal dealing with the “forthcoming campaign” used the words koryaku butai—”invasion force”—aimed at a destination encoded as AF. Rochefort and Layton informed Nimitz that something big was heading toward Hawaii.
In hindsight, it can be seen that Yamamoto’s plans were flawed in the extreme. In setting the three objectives of taking the atoll, establishing control in the Aleutians and luring what was left of the U.S. Pacific Fleet out into the open sea, he was violating the principle of massing his strength. He thought of the Aleutian campaign as a useful feint, a clever deception, as well as a needed blunting of that northern scimitar hanging over the Japanese mainland. Instead it resulted in a ruinous division of his ships and carriers.
Cockiness made him sloppy. He allowed two other carriers to be left behind in home waters—one to be repaired after the Coral Sea battles, the other merely to receive a new complement of planes and pilots—when a determined effort could have added both to his fleet. In addition, when his huge force sailed toward Midway, he placed his four carriers forward in a close grouping that proved terribly convenient for U.S. attack planes. And instead of covering these all-important carriers with his battleships, he had the war vessels, including his flagship, Yamato, lag far behind, a floating headquarters remote from the action.
Most damaging of all was his attempt to use the same deceptive tactics at Midway that had worked for him at Pearl Harbor. Again he used fake radio traffic to create the illusion that his ships were in training operations near Japan. This time, thanks to the delay in introducing the new JN-25 code, Rochefort and his team were not to be fooled.
The intelligence supplied in the Coral Sea battles had confirmed for Nimitz that he could trust his codebreakers. When they began submitting evidence of a massive new Japanese thrust aimed at Midway, he sided with them against the view held by Washington analysts, as well as Washington chief Admiral Ernest J. King, that Rochefort was being duped. The Washington unit believed any move toward Midway was only a feint masking Yamamoto’s real objective: the aircraft factories of Southern California. The U.S. Navy even dispatched a fleet, Admiral Morison has reminded us, to search for a Japanese carrier falsely reported to be descending on San Francisco.
Further, the Washington intelligence staff advised King that Halsey and his carriers should be kept in the Coral Sea, since the Yamamoto offensive might be directed there rather than toward Midway.
Rochefort was not subtle in disparaging these interpretations. Regarding an attack on the U.S. West Coast, he knew the Japanese lacked sufficient transports, tankers and food refrigeration ships to take on so remote an objective. Also, he judged it “ridiculous” and “stupid” to think they would strike so far east while the U.S. Navy ships at Pearl remained on their flank.
As for leaving carriers in the Coral Sea, MacArthur’s codebreaking teams in Melbourne came to Rochefort’s support. Their decrypts verified that the Japanese had abandoned amphibious operations against Port Moresby and were planning an overland offensive instead. Halsey’s carriers could head for Pearl Harbor and Midway.
In his recorded oral reminiscences, Rochefort stated, “Possibly the best thing that ever happened to the Navy during the war was Nimitz’s acceptance of Station Hypo’s estimate of what the Japanese were going to do, not only at Coral Sea but at Midway and subsequent.”
Even with Nimitz’s approval, though, one big question remained. Where was “AF”? Rochefort had worked with the Imperial Navy’s geographical bi-letter designations enough to know that AH was Hawaii and AK was Pearl Harbor. He was sure that references to AF in the intercepts stood for Midway, but none of the decodes made the identification certain. How could he make sure?
Lieutenant Commander Jasper Holmes knew that the Midway command depended on a plant that distilled seawater to supply the garrison’s water needs. What if Midway sent out, both in plaintext and in a low-level code the Japanese were sure to read, that the desalinization plant had broken down and the island’s supply of water was running desperately short? If AF was Midway, surely some mention of this crisis would show up in subsequent traffic.
The scheme was carried out, with the extra fillip of an answering plaintext transmission from Hawaii that a freshwater barge would be sent at once.
The deception worked. As Holmes reported, “The Japanese took the bait like hungry barracudas.” AF’s water troubles turned up in a decrypt, establishing beyond doubt that Midway was the target. Historian David M. Kennedy has called this resourceful stroke by Rochefort’s team “the single most valuable intelligence contribution of the entire Pacific war.” Its upstaging of the bigwigs in Washington, however, exacerbated their ill feelings toward Rochefort.
The ruse convinced Nimitz, who had already reinforced the defenses at Midway. He began preparing his David role against the Yamamoto Goliath, pitting twenty-seven surface warships against the enemy’s eighty-eight. On May 25, Nimitz held a staff meeting that Rochefort had been ordered to attend. A punctual man, the admiral was annoyed when his chief cryptana-lyst showed up a half hour late. But when Nimitz saw what Rochefort had brought with him, all was quickly forgiven. Rochefort and his colleagues had spent the night decoding a long intercept. It revealed nothing less than the complete Japanese order of battle for the Midway attack. Plus, the intercept confirmed that the attack was scheduled not for mid-June, as Washington was claiming, but for June 3 or 4.
On May 28, the Japanese did switch to a new version of their JN-25 code, blacking out the Allied codebreakers for a time. But the changeover came too late. The Americans knew all they needed in order to take on the Japanese fleet.
Unlike the overconfident Yamamoto, Nimitz hastened to amass every element of naval strength he could muster. Although not an aviator himself, he understood the importance of naval air power. On the afternoon of May 27, the battered carrier Yorktown limped from the Coral Sea into Pearl Harbor. If it could be patched up in time, it would add a third carrier to Nimitz’s fleet. Given the extent of its damage, the repairs could easily have consumed a couple of months, perhaps even a trip to the West Coast. Instead, crews swarmed over the vessel and on the morning of May 29 had it ready to put to sea, at least marginally battle worthy.
Nimitz received what seemed a serious setback to his plans when Bull Halsey arrived at Pearl with a skin disease that sent him to the hospital instead of aboard a flagship. Postmortems of the battle, though, suggest that in reality this was a felicitous change. The impulsive Halsey might not have fared as well in the complex operation as his cool, clear-thinking replacement.
This was Rear Admiral Raymond A. Spruance, who in his service under Halsey had shown himself to be an aggressive fighting man and a shrewd strategist. He would command one of Nimitz’s task forces, with Jack Fletcher in charge of the other. Knowing from the Hypo codebreakers that the Aleutian operation was only a diversion, Nimitz sent northward a motley assortment of ships under Rear Admiral Robert A. Theobald.
On June 1, Yamamoto planned to place two picket lines of submarines between Pearl Harbor and Midway. The subs would be stationed there primarily to alert him if the U.S. fleet emerged in response to his surprise attack on the atoll. The operation was badly coordinated, and the subs were late in getting into position, but even if they had been on time they would not have detected the American ships; they had already passed the barrier.
For the previous month the defenses of the Midway atoll had been reinforced by inflows of antiboat and antiaircraft guns, two additional companies of GIs, five tanks, ten torpedo boats, stores of aircraft gasoline and a variety of planes that included B-17 Flying Fortresses. Midway was as ready as Nimitz could make it.
He proceeded to set his sea trap. His two task forces met at “Point Lucky,” 325 miles northeast of Midway, a position that was expected to place them on Yamamoto’s left flank. The three carriers would lie in wait, undetected, while long-range search planes from Midway sought out the Japanese fleet. Then every type of air power the U.S. could marshal, both from Midway and the carriers, would fall on the Japanese ships.
In Washington, suspicions still lingered that Nimitz and Rochefort were being gulled by a Japanese force that was only a decoy. Consequently, they were greatly relieved when on June 3 a flying boat from Midway spotted the invasion fleet almost exactly where Rochefort had predicted it would be. The Spruance and Fletcher task forces, along with the defenders at Midway, knew for certain what they must do.
At this point Yamamoto’s plan began to show its flaws. His battleships, with their powerful eighteen-inch guns, could have pulverized Midway’s defenses, but they were three hundred miles away. The softening up was left to Pearl Harbor’s hero, Admiral Chuichi Nagumo, commanding the invasion fleet that included the mission’s four carriers. At dawn on June 4, Nagumo sent off nine squadrons of bombers escorted by four squadrons of Zero fighters. Their arrival at Midway was expected to be a surprise. Instead, the planes were met by heavy antiaircraft fire and a fierce swarm of game but outmoded and outclassed fighters.
Nagumo’s Zeros shot down most of the U.S. planes. Overall, however, the initial resistance put up by Midway’s defenders seemed to the Japanese leader of the raid too strong to permit a landing of troops. He radioed back to his commander that a second attack wave was needed.
That was not what Nagumo wanted to hear. His ordnance men were already arming aircraft with torpedoes and armor-piercing bombs, preparing to dispatch any Allied warships that might show up, especially the U.S. carriers that Yamamoto hoped to lure toward Midway. A second attack on the island meant canceling that order and equipping his planes with fragmentation bombs for a land bombardment. The necessity for the change, however, seemed to be confirmed by the arrival of a fleet of torpedo bombers from Midway. Even though antiaircraft fire and the Zero fighters massacred the obsolete U.S. planes, their attack verified that the defenders of Midway were far from neutralized. Nagumo sent off a second wave against the island.
While those planes were in the air, he received dumbfounding news: one of his reconnaissance planes had discovered American warships in the area. At first the spotter saw only cruisers and destroyers. Then he reported a carrier. He also warned that more torpedo planes were winging Nagumo’s way. How should he counter this incredible new development? After dithering for a precious quarter of an hour, Nagumo ordered that the returning planes be armed with the original torpedoes and bombs to be used against surface ships.
At that moment of maximum confusion and vulnerability, when the Japanese carrier decks were cluttered with torpedoes, bombs, gasoline hoses and aircraft, came what Gordon Prange in his monumental Miracle at Midway called the Americans’ “uncoordinated coordinated” attack.
Spruance and Fletcher had planned for flights of torpedo planes, dive-bombers and fighters to converge simultaneously over the Japanese fleet, while Flying Fortresses from Midway dropped their bombs from great heights. But Nagumo had changed course, and the American planes had trouble finding his ships. The fighters, running out of fuel, turned back, many of them having to ditch. The torpedo planes, first to discover the Japanese, courageously swept in at low levels. The complete flight was shot to pieces by the Zeros, with only one of the thirty crewmen surviving. They were lost without scoring a hit. The Flying Forts were equally ineffective, managing nothing better than near misses.
The sacrifice of the torpedo planes, though, was not in vain. While the Zeros were occupied with them down near sea level, thirty-seven American dive-bombers from Enterprise arrived far overhead. They had traced their way to Nagumo’s fleet only because their commander, Clarence Wade Mc-Clusky, had cannily let himself be guided by a Japanese destroyer returning after a try at sinking a pesky U.S. submarine. When McClusky and his mates went into their screaming dives, the huge rising suns painted on the flight decks as aids to Japanese fliers gave the Americans perfect targets. McClusky’s crew wrecked the Akagi and the Kaga. A second flight of dive-bombers, from Yorktown, arrived almost simultaneously and concentrated on Soryu.
In less than five minutes the opportunity that had been slipping away from the Americans was turned into a flaming victory. Three of the four carriers were reduced to blazing hulks and later sank. As historian Keegan put it, “Between 10:25 and 10:30, the whole course of the war in the Pacific had been reversed.” George Marshall called it “the closest squeak and the greatest victory.”
The battle was not quite over. The Yorktown, only partially restored from her Coral Sea mauling, was further crippled by a flight of Japanese dive-bombers from the remaining carrier and was finished off by a submarine, which also sank a destroyer. Bombers from Enterprise exacted quick revenge. Her planes caught up with the retreating occupation force and sank the fourth carrier. Also, one cruiser was sunk and a second badly damaged.
Yamamoto still had a vast superiority in sea power, but with the only other two carriers of his fleet protecting the Aleutian landings, he knew he was defeated. He called off the Midway operation and sneaked back to home waters.
The one part of Yamamoto’s overly complex plan that succeeded was his diversionary raid against the Aleutians. Ironically, his small victory there came about because Theobald, the American commander, refused to believe what his cryptographic team told him. Their decrypts warned that while the Japanese would bomb the American base at Dutch Harbor, they would land troops to seize Attu and Kiska. Theobald would not be swayed from believing the invasion would be against Dutch Harbor, and he positioned his ships accordingly. When Yamamoto’s attackers did exactly what the decoders had forecast, Theobald’s task force was in the wrong place by a thousand miles. It failed to prevent the Attu and Kiska landings.
Otherwise, the great surge of Japanese expansion was over. After Midway, despite a few abortive efforts to mount new drives, the war machine of the Rising Sun was put on the defensive.
“Midway was essentially a victory of intelligence,” Nimitz later wrote. George Marshall added that as a result of cryptanalysis, “we were able to concentrate our limited forces to meet their naval advance on Midway when otherwise we almost certainly would have been some 3,000 miles out of place.”
At a postbattle staff conference at Pearl Harbor, Admiral Nimitz singled out Joe Rochefort: “This office deserves a major share of the credit for the victory at Midway.”
One result of the battle nearly caused disaster for the codebreakers. Along with accounts in the American press exulting over the Midway victory was a sidebar story that caused U.S. cryptographic teams consternation and dismay. The story’s headline was NAVY HAD WORD OF JAP PLAN TO STRIKE AT SEA. Appearing in three large dailies owned by Roosevelt-hating Colonel Robert McCormick, the story related that navy commanders knew in advance about Japanese plans, the strength of their forces and the fact that a move against “another base” was only a feint. The gaffe could have cost the Americans their entire intelligence advantage over the Japanese. Investigations found that a reporter aboard American ships in the Pacific had been allowed to see U.S. intelligence summaries and had, with remarkable insensitivity, filed his account, to which equally obtuse censors had given approval. Whether because of this break or as the result of their natural precautions about cryptographic security, the Japanese did make changes in their codes that Allied codebreakers had difficulty in overcoming.