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June 4, 2025 by Peter T Young Leave a Comment

Codebreakers – Secret to Success at Battle of Midway

Around 7:20 Sunday morning, a single-engine Japanese reconnaissance plane entered the cloud-streaked airspace over Pearl Harbor.  Launched earlier that morning from the heavy cruiser Chikuma, the plane circled as the pilot studied the ground below.

Having seen all he needed to see, at precisely 7:35 the recon pilot radioed his report to the striking force, which quickly relayed the information to the Japanese planes now approaching Oahu from the north: “Enemy formation at anchor; nine battleships, one heavy cruiser, six light cruisers are in the harbor.”

The attack on Pearl Harbor set in motion a series of battles in the Pacific between the Japanese and the United States.

With the fall of Wake Island to the Japanese in late-December 1941, Midway became the westernmost US outpost in the central Pacific.

Midway occupied an important place in Japanese military planning. According to plans made before Pearl Harbor, the Japanese fleet would attack and occupy Midway and the Aleutian Islands in Alaska as soon as their position in South Asia was stabilized.

Defenses on the atoll were strengthened between December and April.  Land-based bombers and fighters were stationed on Eastern Island.  US Marines provided defensive artillery and infantry.

Operating from the atoll’s lagoon, seaplanes patrolled toward the Japanese-held Marshall Islands and Wake, checking on enemy activities and guarding against further attacks on Hawaiʻi.

The turning point in the Pacific came in June 1942, when the US surprised and overpowered the Japanese fleet in the Battle of Midway.

That victory was possible, in large part, because of the work of a little-known naval codebreaker named Joe Rochefort.  (Rochefort, responsible for the Pacific Fleet’s radio intelligence unit at the time of the Pearl Harbor attack, felt immense guilt at the failure to predict the Pearl Harbor attack.)

The Japanese Combined Fleet depended on a complex system of codes to communicate by radio. The codes were regularly modified to avoid detection, but in the confusion of the rapid Japanese expansion in the South Pacific the change scheduled for early-1942 was delayed.

The course to Midway started not on a map in a top secret chart room with top strategists and tacticians contemplating Japan’s next move, but was set by the deciphering of messages from the Japanese Fleet.

This was done by a handful of US Navy intelligence officers stationed at Pearl Harbor.

In the spring of 1942, it took cryptanalysts in Australia, Washington, DC and Hawai‘i to achieve the breakthrough that made an American victory at Midway possible.

The Japanese naval code, known as JN 25, consisted of approximately 45,000 five-digit numbers, each number representing a word or a phrase.

Breaking this code, which was modified regularly, meant finding the meanings of enough of these numbers that a whole message could be decrypted by extrapolating the missing parts.

According to one of the leading codebreakers involved, it was like putting together a jigsaw puzzle with most of its pieces always missing.

Leading the codebreaking effort was Station Hypo, the code name for the combat intelligence unit at Pearl Harbor under Commander Joseph Rochefort.

Rochefort included members of the band from the battleship ‘California,’ damaged at Pearl Harbor.  He thought their musical skills might make them adept codebreakers in much the same way that Marine bandsmen used to serve as fire control technicians on ship — the ability to quickly read and play music made them excellent mathematical problem solvers.

By May 8, Rochefort knew that a major enemy operation, whose objective was sometimes called AF, was in the offing and that it would take place somewhere in the Central Pacific.

When they checked this against their partially solved map grid, the found that “A” represented on coordinate of Midway’s potion and “F” represented the other.

His superiors in Washington weren’t convinced; they devised a test that would flush out the location of AF.

The radio station on Midway dispatched an uncoded message falsely reporting that the water distillation plant on the island had broken, causing a severe water shortage.  Within 48 hours, a decrypted Japanese radio transmission was alerting commanders that AF was short of water.

Several days later, he was sure the target was Midway.  As a result, the Americans entered the battle with a very good picture of where, when and in what strength the Japanese would appear.

On June 4, 1942, armed with information from Rochefort and his team, American planes caught the Japanese by surprise and won the decisive battle – it marked the turning point in the war in the Pacific.

In the four-day sea and air battle, 292 aircraft, four Japanese aircraft carriers – Akagi, Kaga, Soryu and Hiryu, all part of the six carrier force in the attack on Pearl Harbor six months earlier – and a heavy cruiser were sunk.  There were 2,500 Japanese casualties.

The US lost the carrier Yorktown, the destroyer USS Hammann, 145 aircraft and suffered 307 casualties. (The inspiration and information in this summary comes from NPS, NPR and Naval History) 

© 2025 Hoʻokuleana LLC

Filed Under: Military Tagged With: Yorktown, Hawaii, Northwestern Hawaiian Islands, Papahanaumokuakea Marine National Monument, Midway, Pearl Harbor, Battle of Midway, Joe Rochefort

June 4, 2024 by Peter T Young Leave a Comment

Battle of Midway

Kuaiheilani, suggested as a mythical place, is the traditional name for what we refer to as Midway Atoll.  Described in the legend of Aukelenuiaiku, the origin of this name can be traced to an ancient homeland of the Hawaiian people, located somewhere in central Polynesia.  (Kikiloi)

According to historical sources, this island was used by Native Hawaiians even in the late-1800s as a sailing point for seasonal trips to this area of the archipelago.

Theodore Kelsey writes, “Back in 1879 and 1880 these old men used navigation gourds for trips to Kuaihelani, which they told me included Nihoa, Necker, and the islets beyond…the old men might be gone on their trips for six months at a time through May to August was the special sailing season.”  (Papahānaumokuākea MP, Cultural Impact Assessment)

Look at a map and you understand the reasoning for the “Midway” reference (actually, it’s a little closer to Asia than it is to the North American continent.)

The Northwestern Hawaiian Islands, and in particular Midway Atoll, became a potential commodity in the mid-19th century. The United States took formal possession of Midway Atoll in August of 1867 by Captain William Reynolds of the USS Lackawanna.

Shortly afterwards, the USS Saginaw, a Civil War-era side wheel gunboat, was assigned to support improvement efforts at Midway where a coal depot in support of transpacific commerce was to be built.

For six months, she served as a support vessel for divers as they labored to clear a channel into the lagoon. In October 1870, the unsuccessful operation was terminated. Saginaw set course for nearby Kure Atoll to check for castaways before returning to San Francisco. The ship would meet a tragic end on the reef at Kure Atoll where she wrecked in the middle of the night.

Midway’s importance grew for commercial and military planners. The first transpacific cable and station were in operation by 1903. In the 1930s, Midway became a stopover for the Pan American Airways’ flying “clippers” (seaplanes) crossing the ocean on their five-day transpacific passage.

The United States was inspired to invest in the improvement of Midway in the mid-1930s with the rise of imperial Japan. In 1938 the Army Corps of Engineers dredged the lagoon during this period and, in 1938, Midway was declared second to Pearl Harbor in terms of naval base development in the Pacific.

The construction of the naval air facility at Midway began in 1940. At that time, French Frigate Shoals was also a US naval air facility. Midway also became an important submarine advance base.

The reef was dredged to form a channel and harbor to accommodate submarine refit and repair. Patrol vessels of the Hawaiian Sea Frontier forces stationed patrol vessels at most of the islands and atolls

The Japanese planned to assault and occupy the atoll in order to threaten an invasion of Hawaiʻi and draw the American naval forces that had survived the attack on Pearl Harbor out into an ambush against the brunt of the Imperial Japanese Navy.

Midway was of vital importance to both Japanese and American war strategies in World War II, and the raid on the atoll was one of the most significant battles of the war, marking a major shift in the balance of power between the United States and Japan.

As dawn approached at around 0430, June 4, 1942, the American carriers (Enterprise, Hornet, and Yorktown) were about 300 miles north north-east of Midway. Their Japanese counterparts (Akagi, Kaga, Sōryū and Hiryū) were 250 miles northwest of the atoll.

In their attack, the Imperial Japanese Navy lost two thirds of its fleet aircraft carriers (four Japanese aircraft carriers and their accompanying aircraft and crews.) The loss of USS Yorktown was a major blow to the US, but the American wartime production of men and materiel would soon make up the difference and outpace that of the Japanese.

While the primary carrier fleet engagement occurred well to the north of Midway Atoll, much of the “secondary” action occurred within or originated from the atoll.

The Battle of Midway (June 4-7, 1942) is considered the most decisive US victory and is referred to as the “turning point” of World War II in the Pacific.  The victory allowed the United States and its allies to move into an offensive position.

In 2000, Secretary of the Interior Bruce Babbitt designated Midway Atoll National Wildlife Refuge as the Battle of Midway National Memorial, making it the first National Memorial designated on a National Wildlife Refuge.

Of all the Islands and atolls in the Hawaiian archipelago, while Midway is part of the US, it the only one that is not part of the State of Hawaiʻi.

Today, Midway is administered by the US Fish and Wildlife Service as Midway Atoll National Wildlife Refuge within Papahānaumokuākea Marine National Monument, a marine protected area encompassing all of the Northwestern Hawaiian Islands.

© 2024 Hoʻokuleana LLC

Filed Under: Military Tagged With: NWHI, Battle of Midway, Hawaii, Northwestern Hawaiian Islands, Papahanaumokuakea Marine National Monument, Midway

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People, places, and events in Hawaiʻi’s past come alive through text and media in “Images of Old Hawaiʻi.” These posts are informal historic summaries presented for personal, non-commercial, and educational purposes.

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