The Allied Offensive: Turning Points of the Pacific War

   On 24 June 1942, King ordered Nimitz to prepare to seize Japanese facilities in the Tulagi area. The Joint Chiefs of Staff approved Operation Watchtower, covering the invasion of Tulagi, its environs and the Santa Cruz Islands on 2 July.  Major General Alexander A. Vandergrift and his 1st Marine Division newly arrived in New Zealand were chosen for this task.  One of the many problems for Vandergrift was the lack of intelligence. Before Pearl Harbor, the Australian Navy established a Coastwatcher network called Ferdinand in the Solomons with government officials and planters.  They were furnished with portable radios and a simple code for reporting potential enemy activities.  This organization would provide intelligence of inestimable value for the next two years.

   On 7 August, the 1st Marine Division attacked Japanese facilities in the Tulagi and Guadalcanal areas.  The prime motivation of this force was to seize the airfield under construction at Guadalcanal before they could make use of it for further advances.  Along with other valuable documents, the current JN-25C codebook was captured.  At Rabaul, Vice Admiral Mikawa responded after getting Yamamoto’s approval for a night attack on the Allied invasion ships.  His lesser force of five heavy and two old light cruisers and one destroyer defeated the superior Allied force of six heavy and two light cruisers off Guadalcanal while Fletcher’s three aircraft carriers, one battleship, and six cruisers were out of range south of Guadalcanal.  The Allies lost four cruisers and the heavy cruiser Chicago lost her bow, with little Japanese damage.  This Battle of Savo Island is covered in detail elsewhere on this web site.

   Hypo had repeatedly reported Japanese cruisers at sea in the Rabaul area and Mikawa’s force had been spotted near Bouganville by an Australian search plane during the day.  However, that latter report was received just hours before the battle due to delays by Australian intelligence units.  Hypo’s interception of Mikawa’s time of departure and Guadalcanal destination message was not decrypted until 23 August due to another code change to JN-25D on 15 August.  This change caused a backlog of messages awaiting decryption.  One knowledgeable writer commented that the result might have been different if Rear Admiral Richmond K. Turner, now in charge of all amphibious forces, had not refused to have an RIU on board his command ship, which was at Lunga Roads just south of Savo Island.  As usual Turner preferred to be his own intelligence officer.  A floatplane from one of Mikawa’s cruisers sent off a tactical report of Allied force locations.  If that had been intercepted timely, the Allied force would have been on the alert and would not have been surprised.

   The avoidance of a potential intelligence disaster with the 1st Marine Division needs telling.  After the first easy conquest of Guadalcanal as apposed to the heavy fighting in the Tulagi area, a Japanese prisoner indicated there were other Japanese who were willing to surrender.  Lieutenant Colonel Frank B. Goettge, the 1st Division’s G-2, obtained Vandergrift’s approval for a small patrol to investigate.  However, the patrol was ambushed and all perished.  One of Goettage’s assistant intelligence officers, Second Lieutenant Ralph Corry was included in the patrol.  As a civilian, Corry had been a cryptographer and translator with OP-20-G, who had worked on JN-25 and other Japanese codes and ciphers.  Had he been captured and talked, the Japanese would have undoubtedly greatly increased the security of their naval codes to the great detriment of the Allies.

   While U.S. radio intelligence was still sketchy during this period, by 22 August it was clear that the Japanese would launch a carrier attack in the Cactus (codeword for Guadalcanal) area by 23-26 August.  The resultant Battle of the Eastern Solomons is covered elsewhere on this web site.

    For the next nine months, the Japanese periodically sent large flights of aircraft to hit Allied transports unloading troops and supplies and to damage aircraft and the airfield at Guadalcanal, named Henderson Field for a Marine pilot killed at Midway.  The Coastwatchers and radio intelligence often gave notice of such raids in time for Allied fighter to intercept them and for ships to get underway.  From early November on, Japanese aircraft activity was often predicted from decrypts, air base traffic analysis and even aircraft radio transmissions by Station AL, the small radio intelligence unit on Guadalcanal.   Of course, the last warning was usually from the radar at Henderson Field, which was generally not enough time for fighters to get to the proper altitude nor for ships to get underway and miss low level attacks.  Station AL also picked up Japanese lookout station transmissions reporting Allied aircraft on their way to bomb ships and facilities in the middle and upper Solomons thus identifying various Japanese enclaves otherwise undetected.

   On 15 September, Chief Radioman James J, Perkins and RM3/c Joe Jilson set up a High Frequency Direction Finder (HFDF) on Guadalcanal as the first increment of Station AL.  A captured Japanese transmitter was used to transmit bearings to NIT, the net control of the Stategic Pacific HFDF Net at FRUPAC in Hawaii, In addition to targets “flashed” by net control, bearings on local Japanese targets in the Solomons and New Britain were passed to local intelligence officers.  The only open space available was on the Northwest corner of Bloody Ridge just after the 13 September battle there.

   On 30 September 1942, the Japanese changed major parts of their communications system including radio call signs.  This deprived radio intelligence experts of many useful analysis tools developed over several years.  It would take a month or so of long hours and feverish work by all concerned to begin to predict Japanese naval actions with any degree of confidence.  As a result, it was only the great work of the Coastwatchers that alerted Allied forces a cruiser bombardment force under Rear Admiral Goto was on its way to Guadalcanal.  With further search plane sightings, Rear Admiral Norman Scott’s deployed his superior forces and defeated Goto’s cruiser-destroyer force in a classic “crossing the T” maneuver.  This 11 October action is known as the Battle of Cape Esperance and is covered elsewhere on this web site.

   On the night of 13-14 October, two Japanese battleships the Kongo and Haruna bombarded Henderson Field and its environs with 918 14” shells of varying types, plus 55 “modified” 12” shells.  It was one of the latter shells that hit 20 feet away from Perkins’ HFDF shack putting it out of operation for a week.  Fortunately, most of the shell fragments went upward from the huge crater it made and the HFDF was repairable.  Henderson Field was unusable.  Also knocked out were most of the aviation gasoline, 32 SBD’s, all the TBF’s, 20 Wildcat fighters, four P-400’s and two P-39’s.  The gunnery officer from the battleship Yamato had been sent to Guadalcanal and directed the fire from Mt. Austen.  Further cruiser bombardments on 14 and 15 October fired 2,250 8” shells against Henderson Field.

   By 15 October, Hypo had established all the call signs and radio frequencies used by two Japanese aircraft carriers and reported positions almost the same as U.S. aircraft sighting reports.

   On 25 October radio intelligence warned of an impending Japanese Army ground assault. The Sendai Detachment attacked the Henderson Field perimeter that night. Forewarned, the Marines were able to repulse the attack.

     Radio intelligence was only able to give some preliminary warnings of Japanese carrier and other forces moving south at this time.  The resultant Battle of the Santa Cruz Islands is covered elsewhere in this web site.  While the exact source is in dispute, a tactical aircraft codebook was recovered from a Japanese plane involved in this battle.  This codebook proved to be of great value to subsequent RIU’s charged with providing early warnings to their fleet commanders.

   Next, radio intelligence warned Guadalcanal officials that two destroyers would make a run the night of 29-30 October.  Cactus planes and PT boats forced the destroyers to depart hurriedly with a portion of their cargo. Subsequently, radio intelligence outlined the scheme to land 540 soldiers, heavy guns, munitions and supplies at Koli Point with 16 destroyers and one light cruiser and a covering force of two cruisers and two destroyers.  While this force was attacked by SBD’s, most of the troops and supplies were landed the night of 2-3 November.  However, most of this force was subsequently wiped out by the Marines and close air support by Cactus aircraft.

   At the end of October, King issued a commendation to all OP-20-G personnel for their work to date. Nimitz passed it along to his intelligence people, but after the November battles he issued one of his own to radio intelligence personnel in Hawaii, the South Pacific, and Australia.

   On 1 November, the IJN implemented another radio call sign change.  A small group of intercept, analysis, reporting and decryption personnel including myself arrived at Cactus by air on 5 November from Hypo.  This augmentation of Station AL was operational at Lunga Point by 9 November.

   On 8 November, Yamamoto issued his operations order for the impending November sea bombardment, and movement of 10,000 troops and 77,606 tons of supplies to Guadalcanal in 11 transports.  In an extraordinary feat, Hypo decrypted that order on 9 November alerting Admiral William F. “Bull” Halsey, the newly installed Commander of the South Pacific (ComSoPac) and Cactus intelligence officers of almost the complete plan.   The subsequent two Naval Battles, denoted Guadalcanal 1 and Guadalcanal 2, are covered elsewhere in this website.  Station AL, as well as other radio intelligence outposts, picked up many of Lieutenant Commander Mitzi’s reports of ships in the harbor from his observation posts on Mount Austen as they were sent by the Japanese radio station at Tassafaronga or repeated on the Rabaul broadcast.  I was on watch the night of 13 November and experienced the great fear of the two twenty minute shelling attacks by the eight inch guns of the cruiser bombardment force.  It had rained earlier so I had to lie flat in the mud of our uncompleted air raid shelter.  The star shell preceding the second attack seemed directly overhead so I sought the refuge of an old Marine slit trench and stayed there despite numerous bites from a colony of fierce black ant that I had disturbed.  In my remaining seven months on Guadalcanal, I experienced about seventy aerial bombings, but none was as terrifying as that shelling episode.

   Radio intelligence warned Rear Admiral Willis A. Lee, Task Force (TF) 64’s commander, to expect an escorted convoy to arrive off Savo between 0030 and 0230 of the early morning hours of 15 November.  Four transports were forced to run themselves aground at Tassafaronga.  Destroyers and SBD’s pummeled the transports and goods that were offloaded.  Other transports were hit hard by SBD’s in the Russells during their retreat northward.

    The failure to get troop reinforcements to Guadalcanal by conventional transports forced the Japanese to try new methods.  First, they began to rely on high-speed destroyers outfitted as transports.  This began the famous “Tokyo Express” down the Slot of the middle Solomons called “rat” runs by the Japanese.  Next, barges were used and referred to as “ant” runs.  Finally, submarines were used to ferry in supplies.  Codebreaking and aerial reconnaissance contributed greatly to the difficulties of Tokyo Express runs made mostly at night from covert locations in the middle Solomons to Guadalcanal and return.

    A 29 November message alerting the Japanese 17th Army to expect eight destroyers and six transports during the night of 30 November was decrypted.  Halsey instructed Rear Admiral Carleton H. Wright to take his TF 67 of four heavy cruisers, a light cruiser and six destroyers to arrive off of Tassafaronga by 2300, 30 November to intercept this reinforcement group.  Despite this specific warning, the U.S. suffered the loss of one heavy cruisers with three heavy cruisers so damaged they were out of action for a year.  The six Japanese transports were not sent for some unknown reason.   Only one IJN destroyer was lost, but most of the drums containing supplies left with the retreating destroyers.   This Battle of Tassafaronga is covered elsewhere in this web site.  As a RM2/c manning Station AL’s direction finder that night, I had an excellent view of the exchange of gun fire while I took bearings on Japanese destroyers’ excited voice transmissions during and after the battle.

   During the first week of December, reinforcement and resupply efforts were limited to submarine runs.  Then, a radio intelligence decrypt foretold the next submarine supply run.  On the night of 9 December, PT 44 and PT 59 ambushed the I-3 and sunk it.  A personal message from Yamamoto and other decrypts gave the composition, timing and destination of an eleven destroyer Tokyo Express run.  SBD’s and MTB’s attacked this force sinking the Teruzuki.  These attacks also only allowed 220 of the 1,200 drums of supplies to be offloaded and received at Guadalcanal.  Although radio intelligence advised of an 11 destroyer Tokyo Express run on 11 December, SBD attacks did not stop this run.  However, PT’s 37, 40 and 48 attacked this force later sinking Tanaka’s flagship the Teruzuki.

    In December and January, radio intelligence produced the plans of Operation KE as to the details of destroyer and submarine transport movements and eventually the dates involved.  However, no hint of its purpose i.e. evacuation of troops was mentioned in such decrypted dispatches.  More information on the evacuation of Japanese troops from Guadalcanal is covered in the Battle of Rennell Island found elsewhere on this web site.  One author recently tried to made a case that the failure to determine that KE Operation was an evacuation of troops vice the normal reinforcement action was one of the worst intelligence failures of the Pacific war.  However, everything was done to stop the KE Operation that was possible and the condition of the evacuated troops was so poor they did not participate in any significant fighting for the remainder of the war.  Thus, any perceived KE intelligence “failure” was far less than Kiska where some 5,500 healthy troops were evacuated without any prior intelligence information at all.

   Numerous decrypted messages foretold of submarine supply visits to Kamimbo, Guadalcanal during the latter part of January 1943: I-20 and RO-40 on the 25th; I-2 on 26/27th with I-1 being delayed two days; I-11, I-25, I-26, and I-32 on the 27th.  Thus alerted the New Zealand corvettes Kiwi and Moa surprised the I-1 at Kamimbo and sank her by ramming on 29 January.  While 50 or so Japanese survivors buried some documents including codebooks, a later salvage operation by the submarine rescue vessel Ortlan recovered many other codebooks, communications and other secret documents from the I-1 and the surrounding waters.  These were brought to Station AL and we carefully dried them out page by page, as we knew their value.  Although the codebooks were mostly superseded, it was very useful to have these complete codes and fleet vocabularies to aid further code recoveries and thus a significant intelligence achievement can be credited to the decrypts of KE Operation messages.

   Also on 29 January, Station AL as well as the RIU on the Enterprise copied Japanese search planes and torpedo bomber attacks on the Chicago, which resulted in its sinking on 30 January.  More about this Battle of Rennell Island can be found elsewhere on this web site.

   To realize the ferocity of the sea battles around Guadalcanal, it is helpful to know that almost three times as many U.S. sailors lost their lives at sea as Marines and soldiers were killed on land.