Intelligence in War: The Value--And Limitations--Of What the Military Can Learn About the Enemy (32 page)

As a result of the Japanese adoption of the new cipher additives to their basic code, JN-25, the result being known to the Americans as JN-25B or Baker, the American cryptographers lost their way into Japanese transmissions during May; or should have done. Because, however, of the difficulty the Japanese found in distributing new additive books across their enormous area of conquest, individual transmitters made the mistake, which may be called a classic mistake so often has it betrayed encryptors, of transmitting messages in both the old and the new code, to ensure accuracy of reception. The Americans, able to read the old code, were thereby enabled to read some of the new, so that by late May they had established the outline of their enemy’s developing plan.

The composition of the attacking force was the first crucial matter to be discovered, though largely by traffic analysis—identifying individual ship call signs and detecting their location—rather than cryptanalysis. On 17 May, Admiral King was able to publish, to a limited circle, an assessment of the strength available to the enemy for what was now believed—but not confirmed—to be an offensive against Midway and the Aleutians. For Midway, it consisted of four fast battleships, two cruiser divisions, two carrier divisions with a fifth carrier attached, two destroyer squadrons and a landing force; for the Aleutians, a cruiser division, a carrier division, formed of the two old, small carriers
Ryujo
and
Zuiho,
two destroyer squadrons and a landing force.

Next day, 18 May, King was able to narrow the geographical frame. A message was intercepted from Admiral Nagumo, commander of the Combined Fleet, reading, “since we plan to make attacks roughly from the northwest from N minus 2 days until N Day request you furnish us with weather reports three hours prior to the time of take-off on said days.” From parallel messages intercepted by the decrypting centres in Melbourne (CAST) and Hawaii it was discovered that the Japanese aircraft for which the weather forecasts were intended would be launched “fifty miles northwest of AF.”
¹⁴

AF was one of the indicators used in Japanese encoded messages to indicate geographical locations. So at least some of the American cryptanalysts believed; unfortunately, others thought otherwise. Commander Edwin Layton, the extremely efficient Fleet Intelligence Officer of the Pacific Fleet, took the view that AF was a geographical indicator and so informed Admiral King in Washington; he specified Midway and Hawaii as the targets of the forthcoming Japanese offensive and Saigon and Ominato, in the Japanese home islands, as the strike forces’ departure points. This assessment arrived at a moment when the various officers of NEGAT (as OP-20-G was code-named) were deep in argument with Admiral Richard Turner’s War Plans Division over what portended in the Pacific. The argument, as so often occurs in bureaucracies, took on a life of its own, separate from the realities of the outside world. OP-20-G had become divided into three sub-branches, OP-20-G1 (Combat Intelligence), OP-20-GZ (Translation) and OP-20-GY (Cryptanalysis). Their counterparts in War Plans began to disagree with the intelligence experts over detail, until a full-scale office war was in progress. Turner, head of War Plans, and Redman, head of Naval Communications, responsible for naval intelligence, eventually came to daggers drawn over the issue of whether the Japanese commander of Fifth Fleet “is to command any force now concentrating in Northern Empire Waters”; Turner, who was senior to Redman, directed him “to assume that Admiral Turner’s views are correct.” Turner, wrongly, took the view that the Japanese offensive would be a continuation of the Coral Sea campaign, Redman that it was directed at AF, which could not be New Guinea.

This at a time when a huge Japanese fleet was gathering to threaten the United States’ last centre of power in the Pacific, Hawaii and its nearby islands, with a potentially devastating attack. What follows cannot be documented, since evidence is lacking. It seems probable, however, that at a local level, HYPO (Hawaii) took steps to resolve the issue unarguably. An undersea cable link, secure from Japanese ears, still operated between Hawaii and Midway, 1,300 miles to the west. The idea of using it deceptively has been attributed to Captain Joseph Rochefort, HYPO’s energetic chief. The story goes that on 18 or 19 May, with Admiral Nimitz’s permission, a cable message was sent from Pearl Harbor to Midway instructing the garrison of the tiny island to report a water shortage, signalling by radio in plain language. On 22 May CAST at Melbourne reported the interception of a message from Japanese naval intelligence in Tokyo (KIMIHI) reading as follows: “The AF air unit sent the following message to [Pearl Harbor] on [May] 20]. ‘Refer this unit’s report dated 19th, at present time we have only enough water for two weeks. Please supply us immediately.’ “ CAST appended, “Have requested [Pearl Harbor] to check this message—if authentic it will confirm identity ‘AF’ as Midway.”
¹⁵

The objective of the coming Japanese offensive was now known: Midway. Subsidiary decrypts identified the Aleutians as a secondary objective; as they were ungarrisoned, that threat could be ignored, even though the islands were sovereign American territory.

Finally, on 25 May, HYPO broke the Japanese navy’s date cipher. By applying the decrypts to old intercepts, Rochefort in Hawaii was able to establish that the attack on the Aleutians would begin on 3 June, the offensive against Midway on the 4th. Nimitz, who reposed great faith in his intelligence decryptors and analysts, accordingly called forward his forces to meet the threat. TF 16 (
Hornet
and
Enterprise
) was recalled to Pearl Harbor on 26 May, to prepare for battle. TF 17
(Yorktown)
was already there, repairing the damage suffered at Coral Sea. He also positioned a submarine screen northwest of Midway to detect the approach of a Japanese strike force.
¹⁶

General MacArthur, commanding in the southwest Pacific, lent important assistance at this stage to Nimitz’s countermeasures, by recommending that radio deceptive measures be instigated, to suggest to the Japanese that a carrier group was still in the Coral Sea. Nimitz agreed, and accordingly the cruiser
Salt Lake City
and the seaplane tender
Tangier
steamed due south of New Guinea exchanging radio traffic that simulated carrier transmissions.

It was fortunate, nonetheless, that OP-20-G and its outstations had, by whatever means, established in late May what the Japanese intended, for the intelligence climate then turned against the Americans. The Japanese relapsed into radio silence, as they had done before Pearl Harbor, while their own listening services, on the alert for any American reaction to the despatch of the Midway strike force from the Inland Sea, began to report a significant increase in what it identified as “Urgent” messages from Pearl Harbor. Japanese intelligence also noted the sighting of American patrol aircraft far west of Midway and the interception of messages from an American patrol submarine in the path of the Midway landing fleet. For inexplicable reasons, Admiral Yamamoto withheld the information from the Midway strike force. It may have been that he did not wish the force to break the radio silence imposed on it by requesting clarification; the result, whatever the motive, was that Admiral Nagumo and his carriers steamed on towards Midway in ignorance of a gathering American riposte.
¹⁷

The complexity of the intelligence plot in the first days of June defies easy exposition. Over the enormous expanse of the Pacific Ocean and its surrounding coastlands, the Japanese appeared to be unchallengeably in the ascendant. Indo-China, thanks to the complaisance of the French Vichy government, was under their control. Coastal China was under Japanese occupation. British Malaya and Burma had just fallen into Japanese hands. British India and Ceylon, with the surrounding waters of the Indian Ocean, were under threat of invasion, following vigorous naval attack. The Dutch East Indies had been occupied, together with most of Australian New Guinea and its outlying islands. The Central Pacific islands, mandated to Japan after 1918 or captured from the Americans and British in the first months of the current war, were Japanese oceanic strongholds. Australia itself, whose Northern Territories had already been bombed by the Japanese, was in a state of defence against invasion. The American-protected Philippines had just surrendered. All that remained to Japan’s enemies as points of resistance to what seemed its inexorable advance to Pacific domination were the American Hawaiian archipelago and its outlying island of Midway.

THE BATTLE OF MIDWAY

Yet the survival of Midway simplified the coming campaign and battle greatly to American advantage. For unless the Japanese attempted a direct assault upon Hawaii, a most unlikely undertaking, Midway was the only place north of the equator—with the exception of the barren and largely uninhabited Aleutian Islands—that was worth their attention; and as recent intelligence in all its forms, decryption, traffic analysis and visual sighting, put the main body of the Japanese navy in or near the home islands, any operation soon forthcoming must be launched north of the equator. Midway must therefore be the target, a conclusion supported by the work of OP-20-G, HYPO and CAST, which allowed King and Nimitz to concentrate the surviving strength of the Pacific Fleet west of Hawaii with confidence.

Yamamoto’s plan was designed to confuse the issue. His fleet was divided into five separate bodies, each committed to a different geographical objective or operational aim. Although the Japanese navy had been created on a Western model, under the guidance of Western, largely British, advisers, its operational methods remained essentially Oriental. Its leaders were well aware of the Western doctrines of singularity of aim and concentration of force. They had failed to rid themselves, nonetheless, of ancient Asian notions of the value of complexity and diffusion. Yamamoto had therefore sent forward, as his first group, a force of ten submarines to patrol the Midway area; second, he had organised a Midway Occupation Force of transports, embarking the landing party, escorts to protect the transports and two battleships and four cruisers to protect the escorts; third, the Carrier Striking Force, commanded by Nagumo, of four large carriers,
Akagi, Kaga, Hiryu
and
Soryu;
the main body of a light cruiser, a light carrier and three battleships, including the brand-new
Yamato,
70,000 tons, 18-inch guns, the most powerful battleship in the world, under his own command; and the Northern Area Force, including four battleships and two light carriers. Counting sub-divisions, the complexity was even greater; it has been calculated that there were altogether “sixteen different groups of warships, all working to a complex plan devised by Captain Kuroshima Kamato, Yamamoto’s senior operations officer.”
¹⁸

The complication was irrelevant. The commanders of America’s Pacific Fleet, after the disaster of Pearl Harbor, the devastation of the air force in the Philippines, the defeat of the Java Sea and the drawn battle of the Coral Sea, had no margin of strength to dabble in diversions. Like a gambler with one last throw up his sleeve, Nimitz had to stake all on the appearance of the enemy at Midway. It was not a blind gamble. The American intelligence organisation had counted the cards. By the end of May the chips were stacked. The outcome depended upon how the hands would be played.

The two American carrier task forces departed Hawaii for Midway in the last days of May,
Enterprise
and
Hornet
(Task Force 16) on 28 May, the hastily repaired
Yorktown
(Task Force 17) on the 30th. Japanese counter-intelligence had probably become aware of American movements, because its traffic analysts had reported in late May that 72 out of 180 American messages originating in Pearl Harbor were prefixed “Urgent,” while the intelligence detachment on recently captured Wake Island reported that American patrol planes were operating in its area, and the Midway Landing Force, which had left Saipan on 28 May, detected an urgent transmission from the American submarine that appeared to be tracking its progress.
¹⁹
So the Japanese knew something; but the Americans knew more: strength, place, time. Most significantly, a HYPO intercept disclosing the departure date of a Japanese oiler, believed to be part of the Midway attack force (MI), suggested, by reason of its known speed, an arrival date near Midway of 30 May.