The Sinking of the Japanese Submarine I-1 off of Guadalcanal and the Recovery of its Secret Documents


Today’s post is written by Dr. Greg Bradsher, Senior Archivist at the National Archives at College Park

Just a little over 75 years ago, in early August 1942, American forces landed on Guadalcanal with the mission of pushing the Japanese forces off the island.  By the end of December, the Imperial General Headquarters (IGH) decided that the Japanese forces, which had suffered great losses at Guadalcanal – on land, in the air, and at sea – would have to be withdrawn from the island.  The Emperor, on December 31, endorsed the decision and the IGH began preparing for the evacuation, called Operation Ke, scheduled to begin during the latter part of January 1943.

Meanwhile, as United States forces continued inflicting great losses on the Japanese forces, the Japanese (on January 14) sent warships to Guadalcanal carrying a battalion of troops to act as a rear guard for the Ke evacuation. A staff officer from Rabaul, New Britain, accompanied them to explain the evacuation decision and plan to the Japanese commander.  What remained of the Japanese 17th Army, some 10,000 men, began moving from the west coast of the island to Cape Esperance in order to be evacuated, while the rear guard checked the American offensive.

During the preparations for the evacuation (which would begin on February 1) at Rabaul, the Japanese submarine I-1 [1] loaded up with about 10 tons of Army rations and set out on a relief mission for Guadalcanal on January 24.  The 320-foot submarine, commanded by Lt. Cmdr. Eiichi Sakamoto and with a crew of 82, was also carrying extra gasoline and had a 47-foot Daihatsu-class landing barge loaded with drums strapped to her.  

Allied cryptanalysts reading Japanese messages on and after January 23 learned that submarine activity at Kamimbo Bay, located near Cape Esperance, on the western tip of Guadalcanal, would involve the I-1 and other submarines on January 26, 27, and 29, but they would not be involved in the evacuation of personnel. On January 25 Admiral William “Bull” Halsey, commander of the South Pacific Area, at Nouméa,  New Caledonia, signaled several of his subordinate commanders that Japanese submarines might arrive at Kamimbo Bay with supplies on January 26, 27, and 29, with time of arrival around 745pm.  The commander of the Naval forces in the Solomons made dispositions to intercept the submarines and sent a signal to all ships at Guadalcanal and Tulagi on January 26, with special instructions to the Royal New Zealand Bird-class corvettes (minesweepers of the 25th Minesweeper Flotilla) HMNZS Kiwi (Lt. Cmdr. C. G. Bridson)  and HMNZS Moa (Lt. Cmdr. Peter Phipps), operating from Tulagi, to go to Kamimbo Bay and take up positions on anti-sub patrol at the northwest tip of Guadalcanal and alerting them that submarines with supplies could be expected that night.

The Kiwi and Moa, were sister vessels, built in Scotland and commissioned in late 1941. They were 168 feet long and 30 feet wide, displacing over 900 ton fully loaded. They had a speed of 13 knots. They were crewed by 35 men and had one 4” gun as well as 2 Hotchkiss light machine guns and one twin Lewis gun. The Lewis gun was replaced in 1942 by a 20 mm gun and in 1943 another 20 mm gun was fitted unofficially. They also carried 40-42 depth charges.  The two ships, along with two other Royal New Zealand Navy ships, the Tui and Matai, left Espiritu Santo in the New Hebrides (now Vanuatu) on December 12, 1942, and arrived at Tulagi on December 15.  Four days later the four ships began patrolling the Guadalcanal area.

HMNZS kiwi

The Kiwi and Moa encountered no Japanese submarines on the night of January 26. They continued their patrol and found nothing on the nights of January 27 and 28.

On the night of January 29, the I-1, after having evaded patrol craft, arrived off the Kamimbo Bay area of Guadalcanal (near Tambea and Cape Esperance), close to the shore near the part of island that is under Japanese control.  At 830pm, I-1 surfaced off Kamimbo Bay in a heavy rain squall and headed for the anchorage. Suddenly, one of the aft lookouts reported a sighting of two torpedo boats. Sakamoto ordered a turn to port and crash-dived to 100 feet, rigging for silent running.  At this point, Kiwi and Moa were patrolling a line off Kamimbo Bay. Kiwi’s ASDIC (an early form of sonar) officer reported a contact at a range of 3,000 yards. Kiwi then altered course and closed the range at full speed until the phosphorescent silhouette of a submarine could be clearly seen. Kiwi then dropped a pattern of six depth-charges. The depth-charges knocked out the I-1’s port electric engine and flooded her aft storeroom. Shortly after, Kiwi dropped another six depth-charges.  This attack disabled the pumps, the steering engine and the port shaft. One explosion ruptured the high-pressure manifold, sending water across the control room. The main switchboard was partially shorted and all lights went out.  As a result of the damage, the I-1 developed a 45-degree down-angle and plunged to an estimated depth of 590 feet, well below its designed limit of 210 feet. A serious leak appeared in the forward torpedo room. Sakamoto ordered the forward group of main ballast tanks blown and full reverse on the remaining shaft. The descent was stopped, but seawater flooded the broken batteries, releasing chlorine gas.

Around 9pm, the crippled submarine surfaced 2,000 yards away on Kiwi’s starboard beam. The Kiwi and the Moa turned towards the I-1 and fired high explosive and star shells. Sakamoto ordered the forward deck gun and the 13.2-mm machine gun atop the conning tower manned. He personally took the helm and had the submarine switched over to her starboard diesel engine and headed for the shore at 11 knots in an attempt to escape the gunfire and run aground. Now all three vessels were exchanging gunfire. The submarine’s forward deck gun sent two shells over the Kiwi and three shells close to the Moa. The Kiwi targeted the submarine at point-blank range with her 4-in deck gun and 20-mm Oerlikon bow gun, illuminating the I-1 with a 10-inch signal searchlight. The Moa meanwhile supported the Kiwi by firing star shells. Kiwi‘s gunners quickly found the range and raked I-1’s superstructure with accurate gunfire, disabling her machine gun and killing Sakamoto and most of the bridge crew and gunners.

The I-1’s navigator, Lt(jg) Sakai Toshimi, appeared on the bridge to find the entire topside personnel either dead or crippled.  The Executive Officer, Lt Sadayoshi Koreeda, proceeded to take command. He ordered what was perceived to be an attempt to capture the boat beaten back. A reserve gun crew was sent up and all officers fetched their swords. Four Arisaka Type 38 carbines carried aboard were passed out to best shooters among the crew.

At 920pm, as the Kiwi altered course to ram the submarine at full speed, the Moa fired illuminating star shells.  The I-1 then altered course to starboard just before the Kiwi rammed it on the port side abaft of the conning tower and holed it. The I-1‘s gunners were unable to hit the attacker, partially shielded by the conning tower structure.  The Kiwi backed off and came under fire from the submarine. Then the Kiwi rammed the I-1 again. This time the glancing blow crushed one of I-1‘s foreplanes. At this point, members of the submarine’s crew begin jumping overboard.  As the Kiwi backed away, her gunners fired into the landing barge strapped to the submarine’s after deck.  The barge burst into flames and lit up the area. In the ensuing exchange of gunfire, a gunshot mortally wounded Acting Leading Signalman Campbell H. Buchanan handling the Kiwi’s searchlight.

The Kiwi then mounted a third ramming from starboard, holing one of the main ballast tanks and then sliding up on the submarine’s afterdeck, and damaging itself in the process. The impact disabled all I-1’s bilge pumps except one and she developed an increasing list to starboard. It was during this ramming, or possibly, during the second one, that the I-1’s navigator, a Kendo 3rd dan swordsman, accompanied by the First Lieutenant attempted to board the Kiwi with swords in hand. They were unsuccessful in their efforts, as they were thrown overboard when the Kiwi pulled back from the submarine. As the Kiwi pulled back the Moa opened fire with its 20-mm Oerlikon bow gun.

The submarine’s Executive Officer, Lt. Sadayoshi Koreeda, then tried to run the submarine aground.  The Moa took up the chase, illuminating the submarine with her searchlight and star shells.  The I-1 was hit repeatedly.  The splashes thrown up by close misses put out the fire raging on her afterdeck.

A little after 11pm, the I-1 ran hard aground on a submerged reef some 300 yards from the beach. The entire after half of the hull was flooded. The foundering submarine developed a heavy list to starboard. Koreeda ordered “Abandon Ship.” Soon thereafter, the I-1 sank as a result of progressive flooding. Only her bow and foreplanes projected some 40 feet out of the water at a 45 degree angle.

About 27 of the I-1‘s crewmen were lost in the attack.  The survivors, led by Lt. Koreeda, reached the shore and joined the Japanese Army garrison the following morning.  They carried with them current codebooks, some secret communications and other documents. Once ashore Koreeda, depending on various accounts, either burned or buried the documents.  Although they had taken some documents with them, the survivors had left behind a case containing the past and future codes, as well as charts, manuals, the ship’s log and other secret documents.

The Kiwi and Moa stood by the stranded submarine until morning, when the Moa sent across a boarding party.  Before being driven off by Japanese shore artillery, the boarding party took a wounded navigating officer, Ensign Kei Akaze, prisoner.[2] They also seized some of the submarine’s documents and charts, which were handed over to the U.S. naval authorities on Guadalcanal.

Early on the morning of January 30, a signal was sent from the Japanese 2nd Communications Detachment at Kamimbo to the Subforce flagship, with information for the 11th Air Fleet and 8th Fleet, explaining that the I-1 had been sunk, the captain killed, and the 47 survivors were at Kamimbo.  A signal was also sent from COMNAVACTSOL (Commander Navy Solomons) to COMSOPAC (Halsey) at Nouméa, stating that the I-1 had been gutted and beached near Kamimbo Bay, one officer had been taken prisoner, and that the Kiwi ‘s bow and ASDIC gear had been damaged so that ship could not continue present operations and would require a refit.

Realizing that he had left behind call lists, old code books, charts, lists of the Imperial Navy’s geographic designators, copies of reserve codes scheduled to go into effect during future months, and other records, Lt. Koreeda decided that the submarine had to be destroyed. On the night of February 2, he, with two junior officers from the I-1, five other crew members, and 11 other Japanese sailors, returned to the wreck with a Daihatsu barge, to attempt to blow up the I-1. Two depth charges and four small explosive charges were strapped to the bow and lower hull of the I-1 in an attempt to detonate the torpedoes aboard. The resulting explosion was too weak to destroy the wreck, but caused enough damage to foil all future attempts to salvage the submarine.

The I-1 survivors eventually made it to Cape Esperance where the bulk of the Japanese were taken off Guadalcanal by destroyers on the nights of February 1, 4, and 7.  They were evacuated to Rabaul, arriving there on or about February 9. There they stated that some current crypto material had been buried ashore where it was possible that the enemy might discover it, and that some classified material had been left on board. Lt. Koreeda, who was amongst the last to be evacuated from Guadalcanal, on February 7, would, at Rabaul, report of the failure to destroy the wreck of the I-1.

The Japanese, concerned about the possible compromise of their codes, decided to destroy the I-1 by air.  During the mid-afternoon of February 10, with about 20 percent of the I-1 still sticking out of the water, eight carrier “Val” dive-bombers, escorted by 28 carrier “Zeke” fighters and 14 other “Zekes” from the 2nd Naval Air Group, bombed the wreck.  One bomb hit the I-1 near the conning tower.  The next day, February 11, the I-2, with the Executive Officer of I-1, Lt Koreeda, aboard, departed the Shortland Islands (just southeast of Bougainville Island) under orders to sink the wreck.

I1Sub inspection
A small boat party sent out by the Army Intelligence looks over a sunken Japanese submarine off the west end of Guadalcanal Island. The submarine was sunk during naval operations off the island and was one of largest type to be build by the Japanese. Date: 2-11-43 (111-SC-243966)

On February 11, U.S. Army intelligence personnel aboard PT-65 examined the wreck of I-1, hoping to gain information about and from it.

Early on the afternoon of February 12 the submarine salvage vessel U.S.S. Ortolan (AM-45), [3] commanded by Lt. Ashley D. Holland, USN, found the submarine in Kamimbo Bay, 300 yards off the shore line, on edge of reef, about 50 feet of bow out of water, lying on a starboard side angle about 71 degrees, in 17 fathoms of water.  The Ortolan returned the next morning commenced diving operations to ascertain the condition of the I-1.  That same day, February 13, after sundown, the I-2, having reached the western end of Guadalcanal, penetrated Kamimbo Bay, failed to locate the I-1 in the dark.

USS Ortolan
War Diary, U.S.S. Ortolan (ASR5), February 9-12, 1943 (NAID 305241)

The Ortolan’s divers on February 13 salvaged a number of water-logged documents from I-1’s conning tower, These included some code books and a list of call signs (ships and stations) dating from 1942.  The Ortolan’s salvage results that day were reported in a priority signal by COMNAVBASE CACTUS (Commander, Naval Base, Guadalcanal) to Admiral Halsey stating the preliminary survey indicated that floating the I-1 was possible and that recovered from the conning tower was a “2 NAVY 4 KANA 1 PROBABLY OTHER SUB CODE.” Instructions were requested regarding the codes.  Halsey immediately responded in a priority signal indicating that the matter be handled as “ZEAL” (alternate term for Ultra) and that the code books or enemy communications data be forwarded to CINCPAC (Commander in Chief, Pacific, i.e., Admiral Chester W. Nimitz) by air as soon as possible. “Indications,” Halsey wrote, “Japs [Japanese] apprehensive regarding secret publications aboard that sub may have a cipher machine also” and expressed his hope that all material could be found prior to floating.

War Diary, U.S.S. Ortolan (ASR5), February 13-15, 1943 (NAID 305241)

On the morning of February 14 the Ortolan moored over the submarine and divers began making a survey of the submarine. Later that day, a badly garbled Japanese message, in which neither sender nor any addresses were identifiable, was intercepted and partly read:

            I-2 at about 1530 the 13th

…Although approached to within 1800 meters could not.

…Off Kamimbo…

…In view of patrol…

…Expect to carry it out tomorrow the 15th

As a result of this message Halsey sent a signal at 1119pm on February 14 to COMNAVBASE CACTUS, stating that there was a belief that the Japanese submarine was still trying to carry out the mission at Kamimbo and another attempt was indicated for February 15.  Another message, indicating the objective may be interference with the salvage operation of the I-1, was also sent to Commander, Naval Base, Guadalcanal.

Divers from the Ortolan continued surveying the submarine on February 15.  That night the I-2 in making an attempt to destroy the I-1 returned to Kamimbo Bay and closed to within 1.4 miles of the coast.  But before she could complete her mission, she was depth-charged, badly damaged, and chased away by American patrol-torpedo boats.

On February 16, as divers from the Ortolan continued surveying the submarine, the I-2 reported that she was then en route to the Shortland Islands.

War Diary, U.S.S. Ortolan (ASR5), February 16-18, 1943 (NAID 305241)

On the morning February 17 the divers commenced diving operations.  At 3:44 pm two divers, in returning to the surface, saw a torpedo pass nearby, about 20 feet deep.  Apparently the I-2 had returned Kamimbo Bay for another attack on the I-1.  The Ortolan sounded general quarters, traced the path of the torpedo, and called on the New Zealand corvette Matai to search to the westward.  The Ortolan brook its moor and assisted in a sound sweep but its search make no contacts.

The Ortolan returned on the morning of February 19, moored over the submarine, and commenced diving operations. The divers that morning recovered a few books. On February 20 divers recovered charts, publications, and other documents.  These included numerous meteorological charts of Pacific Areas, personal sketch maps of Alaska, Midway and Wake Islands, and a booklet of ships’ plans.  On February 21 and 22 divers recovered some code books and other items of interest.  Poor weather and ocean conditions on the morning of February 23 precluded diving operations.  The Ortolan would leave for other duties.  She would subsequently return in February and off and on during to March to engage in salvage operations.  The idea of salvage was eventually abandoned.

War Diary, U.S.S. Ortolan (ASR5), February 19-20, 1943 (NAID 305241)

The salt-water logged code books retrieved by the Ortolan were taken to Station AL (a small intercept, direction finder, traffic analysis, cryptanalysis and reporting station on Guadalcanal). There they were dried by being placed on top of a radio receiver to use its heat.  The records were kept for about two days to get them in shape for transport.  They were taken to the intercept site at Lunga Point, a promontory on the northern coast of Guadalcanal. From there they were sent to CINCPAC’s code breakers at Pearl Harbor.

While the code breakers were trying to exploit the captured code material from the I-1, translators began the task of translating and publishing important documents from the submarine. The U. S. Army Forces in the South Pacific Area (USAFISPA) begins publishing I-1 items in early March. On March 1, the Translation and Interrogation Section, G-2, of the USAFISPA published a notebook containing entries for January 1-29, 1943.  On March 9, the Section published the diary of Seiho Suzuki, 2nd Class Petty Officer, covering the period of early 1942.  The same day the Section published the notebook and diary of Masae Suzuki, covering February 11-September 17, 1942.  On March 13, it published, extracted from list of communications personnel, the organization of Japanese submarine forces.  The next day the Section published communications personnel roster.  The Section on March 16, it published a message written on a communication form for encoding and decoding messages.  On March 18, it published part of a copy of Naval Regulations (Edition of April 1, 1936, with revisions up to June 30, 1942) and on May 30 published the remainder of the regulations.  Also on March 18, the Section published penciled notes, regarding firing torpedoes.  On March 21, the Section published bound notes on ciphers and codes.  On March 30, the Section published the submarine’s operating log covering the period January 1-28, 1943.  The next day it published printed a chart regarding depth charges.  The Section on April 1, published a file of messages and notes dealing with the gunnery section, quartering on shore, orders, and dispatches. A printed chart regarding mechanical mines was published on April 7.[4]

In early July 1943 the Section published a notebook, probably belonging to an officer, which appears to have been kept over a period of several years. It provided a list of ships in commission from December 1, 1939 to June 1940. Also published was a code book table, detailed information about equipment on warships, information on submarines, political commentary, information on aircraft, and numerous names of officers and positions. This translation ran 41 pages.[5]  The published translations continued. In mid-January 1944, the Section published a Japanese publication on Results and Opinions on Items of Essential Engineering Training and Research in the 6th Fleet for the Year 1941, 7th Submarine Division.[6]

The Intelligence Center, Pacific Ocean Area (ICPOA), was also involved in the exploitation of the I-1 documents. On March 16, 1943, it sent to Washington information regarding hydrographic charts, taken from the I-1, noting “these charts are very accurate reproductions of United States Navy Hydrographic Office confidential charts.”[7]  In late March and early April, ICPOA translated and published various documents from the submarine. [8]

All in all, the sinking of the I-1 had been a great success. The documents captured from the submarine provided a wealth of information and intelligence about the Japanese codes and the Japanese navy.[9]

[1] The I-1, had been laid down at Kawaski’s Kobe Shipyard as submarine cruiser No. 74, in 1923 and launched on October 15, 1924; two weeks later was renumbered the I-1. She was a very large submarine displacing a maximum 2135 tons at the surface. She was powered by twin shaft diesel engines and also had two electric motors. She had a speed of 18 knots on the surface and 8 knots submerged. The I-1 had six torpedo tubes and carried 20 torpedoes. The submarine had until January 1943 two deck guns, but at that time the aft gun was replaced with a landing barge.

[2] Akaze was interrogated on February 9, and on February 12, the interrogation report was distributed. COMSOPAC-S-0208, Commander, South Pacific Area and South Pacific Force, February 12, 1943, attached is CIC, SPF, Prisoner Interrogation, Ensign Kei Akaze, Navigator, Submarine I-1, February 9, 1943, Folder: Captured Documents-COMPSOPAC, Box 409, Publications Files (”P” File), 1940-1945, (NAID 1557240) Records of the War Department General and Special Staffs, Record Group 165.

[3] War Diary, U.S.S. Ortolan (ASR5), February 1-28, 1943, Folder, Ortolan, U.S.S., Records Relating to Naval Activity During World War II, World War II War Diaries, December 7, 1941-December 31, 1945, (NAID 305241), Records of the Office of the Chief of Naval Operations, 1875-2006, Record Group 38.

[4] These translations were published as numbered translations by the Translation and Interrogation Section, USAFISPA, Folder: Captured Documents-Combat Intelligence Center-South Pacific Area, Box 403, Publications Files (”P” File), 1940-1945, (NAID 1557240).

[5] Translation Item No, 606, Translation and Interrogation Section, USAFISPA, July 12, 1943, Folder: Captured Documents-Combat Intelligence Center-South Pacific Area, Box 402, Publications Files (”P” File), 1940-1945, (NAID 1557240).

[6] Translation Item No, 1115, Translation and Interrogation Section, USAFISPA, January 19, 1944, Folder: Captured Documents-Combat Intelligence Center-South Pacific Area, Box 406, Publications Files (”P” File), 1940-1945, (NAID 1557240).

[7] R. H. Hillenkoetter, Officer in Charge, Intelligence Center, Pacific Ocean Areas to Vice Chief of Naval Operations (Director of Intelligence), March 16, 1943, File A-1-Z. Register No. 24097, Top Secret Reports of Naval Attaches 1940-1945 (NAID 595101), Box 93, Intelligence Division, Office of Naval Intelligence, RG 38.

[8] ICPOA, Translations of Captured Japanese Documents, March 29 and April 9, 1943, Folder: CINCPAC-CINCPOA Translations of Captured Japanese Documents, (Entry 79) Box 528, Publications Files (”P” File), 1940-1945, (NAID 1557240).

[9] Among the secondary sources used in writing this blog were Alan Stripp, Codebreaker in the Far East (Oxford: Oxford University Press, 1989); John Winton, Ultra in the Pacific: how breaking Japanese codes & cyphers affected naval operations against Japan 1941-45 (London: Leo Cooper, 1993); Joseph D. Harrington, Yankee Samurai: The Secret Role of Nisei in America’s Pacific Victory (Detroit: Pettigrew Enterprises, 1979); W. Jasper Holmes, Doubled-Edged Secrets: U.S. Naval Intelligence Operations in the Pacific During World War II (Annapolis: Naval Institute Press, 1978); John Prados, Combined Fleet Decoded:  The Secret History of American Intelligence and the Japanese Navy in World War II (New York: Random Hill, 1995); Michael Smith, The Emperor’s Codes: The Breaking of Japan’s Secret Ciphers London: Bantam, 2000); and, Richard B. Frank, Guadalcanal: The Definitive Account of the landmark Battle (New York: Penguin Books, p, 1992). Also useful was the website:

2 thoughts on “The Sinking of the Japanese Submarine I-1 off of Guadalcanal and the Recovery of its Secret Documents

  1. Really interesting. And who really thought about salbage operations. That had to have been interesting as well as dangerous

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