The Bougainville Invasion (Part 4): March 1944 – May 1944

With this submission, CINCLAX’s in-depth review of this part of the Solomons campaign is complete. I think you will agree with me that considerable thought and work went into these articles and join me as a hearty “BZ” is passed his way.  On the horizon – inthe next few weeks we will wrap up the action at sea and then give each of the authors a chance to (briefly) state their analysis as to the relative importance of Midway vs. The Solomon Islands campaign. – SJS

Completing the Cartwheel – the Final Encirclement of Rabaul

Meanwhile at Cape Gloucester and Manus…

Almost contemporaneous with the 3rd Marines departure from Bougainville, the now well-rested 1st Marine Division of Guadalcanal fame was loaned to RADM Dan Barbey’s 7th ‘Phib for a December 26, 1943 landing at Cape Gloucester on the western tip of New Britain. This followed an insignificant diversionary Army landing 10 days earlier at Arawe on the southwestern coast. While the Cape Gloucester Marines succeeded in capturing an airstrip, this field never became a significant factor in the continuing reduction of Rabaul, and turned out to be a rather wasteful operation that cost some 248 lives. The Japanese force at Cape Gloucester had no artillery with which to close Dampier Strait, so it had been no threat to Allied operations. It was monsoon season, and daily rainfall could reach 16 inches; thus the 1st Marine veterans opined the terrain and weather conditions were as big an obstacle as the Japanese, and the mud even worse than Guadalcanal.

On February 29, 1944, MacArthur’s 1st Cavalry Division landed on Los Negros Island in the Admiralties (north of New Guinea), then a week later on Manus Island to seize the magnificent Seeadler Harbor. Later in the year, this would be an invaluable staging place for operations on Palau and Leyte.

Such was the work of the weaker of the two arms of the South Pacific campaign to “Break the Bismarcks Barrier.” Now it was up to the stronger arm, Halsey’s, to complete the reduction of Rabaul.

AirSols Campaign, 1944

By late December 1943 Rabaul’s five airfields had been severely damaged by continual Allied bombing. Few hangars and service buildings remained undamaged. In response, the Japanese went underground, excavating new facilities in the soft volcanic soil. Their great manpower included some 98,000 Japanese Army and Navy troops, 1457 Chinese slave laborers, and about 6000 Indian prisoners of war who had been captured at Singapore. As a fortress, Rabaul was perhaps the strongest bastion in the entire Pacific; it had some 43 coastal guns, 367 antiaircraft guns (numbers vary here), as well as tanks and field artillery. Moreover there were still millions of tons of supplies and munitions, some in dumps extending over a square mile. Since its conquest in 1942, the Japanese had planned for Rabaul to be the jumping off point for expansion to the south all the way to Australia. As they never got further south than Guadalcanal, there was a lot left over.

For some time MacArthur had insisted upon invading Rabaul, but now the Allies concluded that Rabaul should simply be isolated and bypassed. After the damaging carrier raids of early November, the IJN had withdrawn its ships to Truk. Now only aircraft remained as a force, and Air Sols thus began continual air strikes against the fortress to negate it as an airbase.

By late January 1944, MG Ralph Mitchell USMC of the 1st Marine Air Wing had become CO of AirSols, and had moved his HQ up to Cape Torokina.

In fact he had already launched his air offensive. Because they employed many of the same aircraft (F4U, SBD, TBF) as the carriers did, Mitchell had his pilots briefed by carrier pilots who had participated in earlier strikes.

Mitchell launched his first big strike on December 17th, largely a fighter sweep to beat down the defenders. At that time, the Japanese had approximately 140 fighters (Zeros), 60 heavy (G4M Bettys) and 50 light bombers (B5N Kates) in all of the Bismarcks. Most of these aircraft had been stripped from Third Fleet carriers at Truk. Against this, AirSols could boast 268 fighters, 252 light and medium bombers (B-25s), and 631 heavy bombers (B-17, B-24) at its disposal.

Each side lost two planes in this December 17th strike, while a second strike on December 19th included B-24 Liberators as bait; losses were five Allied and four Japanese aircraft. Up against the best that the IJN could offer, Allied pilots noted that the Japanese skill level seemed to have jumped. considerably; by year’s end the total score was 40 Japanese aircraft destroyed for losses of 24 Allied aircraft, and only 192 tons of bombs had been dropped. Japanese operational losses—always a considerable percentage in their land based campaigns—are unknown but certainly must have been in the several dozens.

The new year saw a shift in focus. The heavy bombers stayed home and so-called “light bombers” (carrier-types) carried the ball. Still, results were not outstanding. On January 7th a raid claimed only two enemy planes in air combat and five on the ground, while the Allies lost a total of five.

Another raid on January 14th cost the Allies four aircraft versus three for the enemy. Three days later, AirSols claimed its first ship kills in the campaign; when four transports and a salvage vessel were sunk.

Intensity and frequency continued to increase, and by late January the Allies began to take rising tolls of the enemy while minimizing their own losses. After some three more weeks, the air battle was over. The final combat over Rabaul came on February 19th. AirSols found little shipping in the harbor, and so expended their munitions against the airfields instead. Meanwhile ADM Spruance had pulled off his landmark raid on Truk two days earlier, and probably as a result, the IJN withdrew nearly all its aircraft on February 20th. Two transports carrying around 350 ground personnel headed for Truk were bombed and sunk by AirSols on the 21st.

A Curious Visit

At this seemingly critical juncture for the Japanese, Prime Minister Tojo Hideki chose to show up for an “inaugural call” on Rabaul. Accompanying him were Chief of Naval General Staff ADM Nagano Osami and Navy Minister ADM Shimada Shigetaro. From Rabaul’s standpoint, this was really something of an affront. Tojo told GEN Imamura to hold Rabaul at all costs, but offered him no further help.

History does not record whether or not the Pearl Harbor Fleet Intelligence Unit ever intercepted any messages regarding this trip, as they notably had about Yamamoto’s 1943 fateful trip to Bougainville. This begs the question whether or not Nimitz would have acted even had he known of Tojo’s trip.

Victory—Almost

So Allies had finally won the air campaign over Rabaul, neutralizing any possible offensive capacity from the base. From November 1943 through March 1944, Japanese losses were estimated at 359 aircraft. AirSols combat losses were 136 aircraft. Still, daily raids—now referred to as “milk runs” continued. Supply dumps and antiaircraft gun positions, were the principal targets—as well as keeping the runways cratered.

Despite AirSols’ best efforts, the Japanese managed to preserve over half their antiaircraft guns by continuing to move them frequently from one pre-pared position to another. They’d been at this for over a year now, and were some of the best and most experienced AA crews in the world

In March the emphasis shifted to incendiary attacks on supply dumps by New Zealand pilots, which forced the Japanese to move their considerable remaining stores underground. AirSols’ motto became “Keep Rabaul Burning,” and by April only some 122 buildings were left standing—out of an original total of about 1400

Once the Zeros left Rabaul in February, AirSols now found itself with a large surplus of fighters. So, taking a page from their book of improvisations, almost all fighters now became fighter bombers. Army P-38s, P-39s, and P-40s, and RNZAF P-40s, were fitted with bomb racks, after which they joined the B-24s and B-25s in making regular bombing attacks. Initially Navy and Marine fighters confined their attacks on ground targets to strafing runs, but later in the year all fighter aircraft carried bombs. In time, the Corsair would become the workhorse Navy ground attack and CAS aircraft until the advent of the AD Skyraider in the 1950s.

After bombing Rabaul town into rubble, B-24s, B-25s, SBDs, and TBFs took up the task of hitting the two largest enemy supply dumps, one about two miles west of Rapopo airfield and the other on the peninsula’s north coast three miles west of Rabaul. After disappointing results with standard HE 500 pounders, the pilots found that bombs containing clusters of 128 smaller incendiaries were more effective in destroying the sprawling areas of storage tents, sheds, and ammunition piles. One near Rapopo measured slightly more than a square mile!

Until late March 1944, the 13th Air Force’s B-24s sent around 24 planes a day to Rabaul. Similar numbers were also mustered by the 13th’s B-25 group After that, all heavy bombers were diverted to attacks on Truk, about 760 miles north of Rabaul. Over the course of three months, during which the major destruction of above-ground installations was accomplished, an average of 85 tons of bombs a day was dropped on Rabaul targets. The strength of Marine and Navy SBDs and TBFs varied, but usually there were three SBD and three TBF squadrons at Piva and three SBD and one TBF squadron up at the Green Islands (see below); in all about 160-170 planes were available, with a third to a half that number in daily use. Gradually these attacks were supplemented by fighter bombers. Night “heckling” missions also began, with the object being to have at least one plane over the target all night long.

Redeployment and Realignment

Rabaul’s new impotence brought changes in the dispositions of Allied forces in the South and Southwest Pacific. Beginning with the start of the New Georgia operation (July 1943), most of the combat troops, planes, and ships assigned to Halsey’s command had officially operated in the SWPA under MacArthur’s strategic direction, although the general almost always gave Halsey a free hand.

But on March 25th 1944 the Joint Chiefs of Staff directed a redeplyment of forces to take effect on June 15th. Now the bulk of SoPac assets were assigned to MacArthur’s operational control for the advance through New Guinea and the Admiralties to the Philippines. He would get the Army’s XIV Corps Headquarters, plus six infantry divisions. Added to ADM Kinkaid’s Seventh Fleet were 3 cruisers, 27 destroyers, 30 submarines, 18 destroyer escorts, an amphibious command ship, an attack transport, an attack cargo ship, 5 APDs, 40 LSTs and 60 LCIs.

All Marine ground forces in the South Pacific were now assigned to ADM Nimitz’ command, as CinCPOA, to take part in the Central Pacific drive to the Marianas and beyond. However most Marine air units remained with SWPA to be the core strength of the continued blockade of bypassed enemy positions in the Solomons and Bismarcks. In retrospect this was not a particularly wise decision, as the Marine air-ground cooperation had really begun to take root on Bougainville, and in future time would become a staple of Marine doctrine. The stage was thus set for the Halsey-Spruance Third Fleet-Fifth Fleet command arrangement.

However a part of the new assignment of forces brought an instant howl from the Royal New Zealand Air Force units, which had played such an important role in AirSols since Guadalcanal days. The JCS had relegated the RNZAF to SoPac garrison duty, and this decision was completely unacceptable to the New Zealand Government, which insisted its forces continue their front line role in the Pacific. The New Zealand Minister in Washington protested, and the result was the allocation of seven squadrons–four fighter, two medium bomber, and one flying boat—to the SWPA and seven squadrons of the same types to the South Pacific. Really this was an easy decision, as by this time all RNZAF units were either equipped or in the process of being equipped with U.S.-manufactured aircraft. This made for an ease of maintenance and resupply in areas that would be manned primarily by U.S. Navy and Marine units. Under the final plans, the deployment of the RNZAF to assigned SWPA bases, Bougainville, Los Negros (Admiralties), Emirau, and Green, would not be completed until late in the year.

The Green Islands

Before the encirclement of Rabaul could be completed, there were two modest land operations to accomplish. The first was the Green Islands, just 37 miles north of Bougainville. This was an eight-mile-long by four-wide oval ring, of three coral and sand islands around a lagoon. Most important, they were only 117 miles from Rabaul and had a good spot for an airstrip.

Halsey had been thinking of the Green Islands for some time, even before Hyakutake’s last offensive on Bougainville in March. It was an offensive he could do “on the cheap,” which was an important consideration, as SOPAC was allotted only about 15% of Navy-Marine Corps strength in the Pacific. With Fifth Fleet Central Pacific operations underway or on the horizon (Gilberts—November 1943, Marshalls—February 1944, Marianas—June 1944), Halsey knew he could not count on additional forces from Nimitz.

Fortunately he enjoyed some “hidden” assets in the form of the 3rd New Zealand Division. As early as January 1944, 300 men of the 30th New Zealand Battalion, along with Navy Seabees and engineers went ashore in the Green Islands to do extensive hydrographic studies and find locations for an airfield. Of equal importance, from local natives they learned there were only about 100 Japanese defenders.

On February 15th the task of taking the island fell to the 5,800 men of the 3d New Zealand Division under MG H. E. Barrowclough; there was also a contingent of American soldiers, Seabees, and engineers, and cover from AirSols Marine planes. The always-reliable RADM “Ping” Wilkinson had TF 31, whose cruisers and destroyers were made available for any shore bombardment requested. Considering the opposition, it was overkill.

On February 14th Japanese float planes spotted the large Allied convoy was on the way, shepherded by destroyers and cruisers. Aircraft from Rabaul and Kavieng (New Ireland) attacked by moonlight, but to no avail. By 0800 all the Kiwis were ashore, unopposed, on the main island of Nissan. Then some Vals (D3A) arrived but Allied antiaircraft fire and Marine fighters drove them off without scoring a single hit. New Zealand patrols received light resistance, a few brief firefights. By February 19th the Seabees began building an airfield on the island, and by March 4th a B-24 could make an emergency landing on “Green,” as the strip was soon called.

Emirau – the Very Last Step in the Solomons Campaign

As planning for the Green Islands operation proceeded, Halsey continued to look for ways to avoid landing on New Ireland to capture Kavieng. In late December 1943, therefore, he directed “Ping” Wilkinson to prepare for the seizure and occupation of Emirau Island. Emirau is in the St. Matthias Group, about 75 miles northwest of Kavieng. Approximately eight miles long by four miles wide, Emirau is fairly level, although undulating and densely wooded. It had been completely undeveloped in pre-war times. Nevertheless there were several suitable sites for the all-important airstrips.

MacArthur temporarily threw a monkey wrench in the planning works, as he continued to advocate an amphibious attack on Kavieng; thus Wilkinson’s Emirau preparations were delayed. Fortunately saner heads prevailed and in March MacArthur realized how strongly Kavieng was defended. To seize such a stronghold would require more troops, ships and supplies than were then available to South Pacific Forces. Taking a page from earlier Allied by-passing in the Solomons, it was clear that Kavieng could also be neutralized if the Allies were to occupy islands north and west of that town. With that move the Solomons and Bismarcks would be completely cut off from the Empire. Japanese reinforcements and matériel could no longer be poured into or out of these positions. At Emirau forces of the South and Southwest Pacific came together, there to unite for a drive through the Philippines toward Japan.

D-Day was set for March 20th. Selected to make the landing was the 4th Marines, a regiment which had once been the storied “China Marines” and had then been part of the desperate defense of Bataan and Corregidor. Now it was reborn as a new, independent regiment, largely composed of battle-hardened veterans from the old raider battalions, which were now disbanded.

For a diversion and to generally keep Japanese heads down. RADM Robert Griffin took his old battleships, New Mexico, Mississippi, Tennessee, and Idaho, to bombard Kavieng on D-Day. The four old battlewagons were learning their shore bombardment role; later in the war this proficiency would serve the Navy and Marine Corps very well.

The 4th arrived at Emirau shortly after 0600 on March 20th. The Marines and sailors fired a few shots at basically nothing; then the amtracs opened up. Even before the island was secured the Seabees got right to work on two airfields. In quick time they laid out a 7,000-foot bomber strip and a 5,000-foot stretch for fighters.

Occupation was completed early the following, as there was no Japanese opposition. BG Noble now organized his troops for defense; antiaircraft emplacements were built, protective trenches dug, trails cut; and all other installations such as the creation of an artificial beach (for LST unloading) were progressively developed.

Within a month, 18,000 men and 44,000 tons of supplies had come ashore and a PT base had been established. In early May the first airstrip was complete. With the occupation of Emirau, the Solomons Campaign was concluded. For the Americans, the war would now move north.

Australian Aftermath – December 1944 – August 1945

In December 1944 the Americal and 37th Divisions departed Bougainville. Already the importance of the Torokina airstrips was declining, and there was little for AirNorSols—the new designation for AirSols—to do. Rabaul had long been encircled and successfully neutralized. Defense of the perimeter was now left to the Australian II Corps, under the command of LTG Stanley Savige. He had four brigades from the 3rd Australian Division (about 20,000 total), all of whom had seen many months of heavy fighting in the jungles of eastern New Guinea.

This would prove to be an unpopular assignment for the proud and experienced Diggers. They had been on the frontline of the war since early 1942; now they were tasked with what looked distinctly like a rear echelon clean-up mission which would make little or no difference in the war; the front had now moved far north to places like Leyte, Lingayen Gulf and the Marianas.

When they left, the Americans told the Australians they estimated about 12,000 Japanese remained on Bougainville. The Aussies thought there were double that, but in fact there were nearly remaining 41,000 under GEN Hyakutake’s 17th Army command. More troubling, some 8,000 were in forward areas near the perimeter. Would they choose to attack once again?

Bonis Peninsula in the North

Unlike the Americans, who had not expanded their perimeter since the March 1944 Japanese offensive, the Australians took a different tack. There was a war on, after all, and if there were Japanese troops to attack… Accordingly a brigade was sent north to the Bonis Peninsula and to patrol towards the Buka Passage.

Soon deadly Japanese raids ambushed ration parties and cut signal wires behind Australian lines, so on July 22nd, 1945 orders were given for the

23rd Brigade to concentrate on a 3,000 meter front around the Buoi plantation, where the Japanese were strongly entrenched in well-camouflaged positions, After two days of heavy fighting, the Japanese abandoned the position. For their part, the Australians now left well enough alone in northern Bougainville

Southern Bougainville

The 3rd Australian Division was given the somewhat unwelcome role of taking the attack to the Japanese in south Bougainville. Why the Aussies, with all their prior experience in very difficult jungle terrain, would want to tackle it again remains a mystery, when they could easily have followed the American practice of remaining on the defensive and letting the Japanese come to them in costly attacks. At the time, many Diggers thought their country’s involvement was mostly a political move to demonstrate their country’s continued participation in the war. They could have been correct.

In late November 1944, the 29th Brigade began extensive patrols to the south along the coast. There was some Japanese resistance, but the Australians managed to advance some 13 miles over two months. The 29th was relieved on January 23rd by the 7th Brigade on the Puriata River—about 30 miles from Japanese HQ at Buin. Intelligence indicated that the Japanese would then launch a major offensive in early April 1945, and they did—with moderate losses for nothing gained. By now the Japanese attack was exhausted.

The Aussies took up their own offensive on April 17th, on the Buin and Commando Roads. First Japanese resistance was light but as the Australians neared the Hongorai River, it stiffened with forward infantry coming under frequent artillery fire causing casualties. After three weeks of fighting to gain all of 7000 yards, the Hongorai was finally reached on May 7th. The cost had been 120 killed or wounded; 169 Japanese dead were counted.

The Japanese were driven from the ridge overlooking the Hongorai and the main Aussie advance resumed on June 2nd behind heavy air and artillery bombardments. Patrols were on the Hari River by June 5th, but when the main body advanced along the Buin Road (the East-West Road) it met heavy fire and its tanks were delayed by swamps. The Japanese put up a strong defense in front of the Mobia River which was reached on June 25th. The next objective was the Mibo River, which was reached in July.

Further inland, an Australian-led contingent of native guerrillas created a reign of terror among the Japanese troops in what was the only large-scale example of native assistance to the Allies on Bougainville. It is estimated that this force killed over 2,000 Japanese in its eight months of operations. Unlike all other islands in the Solomons, where the locals had been helpful and friendly to the Allies, they had usually been somewhat hostile on Bougainville—perhaps because of the residual influence of the German missionaries who had stayed on after the Japanese arrived.

The 29th Brigade returned to the front lines and was scheduled to head south across the Mibo River on July 3rd, but continuing downpours caused a series of postponements. Before the offensive could be launched, news of the Japanese surrender came, and with that all active patrolling on Bougainville ceased on August 11th. Japanese 17th Army commander, LTG Kanda, waited until the surrender at Rabaul on September 3rd before surrendering his Bougainville command.

It is estimated that a total 65,000 Japanese were on the island when the Americans first landed in November 1943. A year later when the Australians took control the Japanese numbers had shrunk to 41,000 although this number was twice the Australian strength.

During the Australian part of the Bougainville campaign, 516 Australians were killed and 1,572 were wounded. About 8,500 Japanese were killed, while some 9,000 died of disease. 23,500 surrendered to the Australians in September 1945.

Rabaul – The Real “Gibraltar of the Pacific”

It seems only fitting to close this series on the Solomons Campaign with some observations from the Japanese viewpoint on the ultimate target of Operation Cartwheel: Rabaul.

During and after the war historians of all stripe consistently referred to the Japanese Combined Fleet bastion at Truk as “the Gibraltar of the Pacific,” implying that it was virtually impregnable to amphibious assault. But in only two 1944 days (February 17th-18th) American carriers and battleships attacked, sinking some 47 ships and destroying 270 aircraft. A follow-up raid on April 29th-30th was mounted, destroying about 100 planes. From that moment on, Truk was neutralized and effectively out of the war. Its garrison of about 7,500 Army and 4,000 Navy troops were marooned there without food and supplies until war’s end, and reportedly incidents of cannibalism occurred. Some Gibraltar! A look at the facts and statistics, however, reveals that Rabaul was the true champ—even stripped of its aircraft.

Rabaul’s Favorable Geography

By the end of 1944 Rabaul had become one of the most heavily bombed places on earth, yet its 100,000 Army and Navy troops were largely untouched because they had gone underground, as had many of its multiple gun emplacements. Most of the extensive anti-aircraft units continued to survive, as they moved on an almost daily basis. Their crews were undoubtedly some of the most experienced in the world; after all, they’d had almost daily practice for well over a year!

It was geography which made Rabaul so impregnable. Its inner anchorage, Simpson Harbor, had space for nearly two dozen 15-20,000 ton ships, while the capacity of its outer roadstead, Blanche Bay, was more than triple that. Tempting targets were the large collection of war and merchant ships that often congregated there through 1942 and 1943. It was getting in to bomb them that was the problem, and the only good way in was up from the St. George’s Channel.

On three sides the anchorages were tightly surrounded by steep mountain peaks (including three active volcanoes), and it was on this high ground that the Japanese placed many of their anti-aircraft guns. Any attacker who attempted to conventionally torpedo or dive bomb had to fly through a hail of flak. Figures vary, but many Allied pilots thought that 50% of their combat losses were to AAA.

GEN Kenny’s Fifth Air Force skip bombers were thus taken out of the equation. The wave-hopping skip bombing techniques that had wrought such havoc at the Bismarck Sea Battle in February 1943 were unable to repeat their performance at Rabaul, and usually his attacks from Dobodura (New Guinea) were limited to high level B-24 and B-25 attacks from 15-20,000 feet. From that altitude they almost never hit any ships and had to content themselves with cratering runways and destroying the town.

Until their final withdrawal in February 1944, IJN Zeros had made life very difficult for both AirSols and 5th Air Force attackers. Along with the Val (D3A-1 & 2) dive bombers Kate (B5N) torpedo bombers, in great part these planes were flown by Japan’s best pilots and were often stripped from Third Fleet’s carrier air groups.

With their increasingly limited aircraft production capabilities, Japan could ill afford the virtually catastrophic attrition they suffered in the Solomons, and had never been able to rebuild their air groups. At the Philippine Sea in June 1944, the first carrier vs. carrier battle in 21 months, the IJN lost over 400 planes in the “Turkey Shoot” without inflicting hardly any damage at all on Spruance’s 5th Fleet. Never again would Japanese Naval airpower be a force to be reckoned with. The Americans could thank AirSols for the low quality of their opponents.

Now, the pilots in Ozawa’s best carrier division averaged just six month’s training, while those with Carrier Division 3 averaged only three months and those with Carrier Division 2 just two months. The Japanese aviators were simply no longer a match for the Americans. Nor were their aircraft.

FORTRESS RABAUL—The extensive pre-war plantations provided the Japanese with ample flat land for additional airstrips. The inner and outer harbor installations were built around a sunken caldera, caused by magma-displacing eruptions from surrounding volcanoes. Vunakanu and the “downtown” airfield Lakunai had been built before the war; the Japanese improved them and built three others. The Gazelle Peninsula area around Rapopo became the location of enormous supply dumps, as well as the fighter director radar.

Since its capture from the Australians in 1942, the responsibility for the defense of the Rabaul area was always understood to be a dual one, with some 80,000 Japanese Army and 20,000 Navy troops holding separate sectors on the ground and the IJN providing almost all the aircraft. Unlike elsewhere in the Empire, at Rabaul cooperation between the two branches was always outstanding. LTG Imamura Hitoshi, 18th Area Army commander, and RADM Kusaka Junichi, CO 11th Air Fleet, enjoyed a long, happy relationship. Kusaka was a cousin of long-time Kido Butai and later 1st. Mobile Fleet Chief-of-Staff, Ryunosuke.

RABAUL COMMANDERS—LTG Imamura (left), who had the unenviable task of defending the base ‘til the bitter end. After the surrender he was tried as a war criminal for abusing prisoners, and sentenced to 10 years in prison. VADM Kusaka (right) commanded the 11th Air Fleet.

The Tunnels of Rabaul

Despite the mass AirSols raids throughout the spring of 1944, Japanese troops at Rabaul were surprisingly better off than Allied aerial observers could estimate. What they could not tell was that the Japanese were continually dispersing a large portion of their supplies, ammunition out of sight under ground and south of the airstrips, under cover of the jungle. Every able-bodied man was ordered to dig caves and tunnels for the day when the presumed Allied landing would come. Supplementing the Japanese Army and Navy troops were some 6,000 Indian soldiers captured at Singapore, plus about 1,500 Chinese slave laborers. Hospitals, artillery emplacements, barracks, ammo dumps and ammo factories, repair shops, air raid shelters and the like were built into a maze of tunnels and caves that would eventually total nearly 350 miles in length, although estimates vary, and even today additional tunnels are occasionally uncovered. Tunneling continued until the end of the war, and turned Rabaul from a base into a formidable fortress, anticipating an Allied amphibious attack they so desired but that never came.

The defenders had endured almost daily pounding from Allied aircraft; some records show 29,354 sorties having dropped 20, 967 tons of bombs! Notwithstanding this impressive amount, the Japanese still had plenty of guns left untouched. Immediate post-war inventories and interrogations revealed only 93 out of a total of 367 antiaircraft guns, one of 43 coast defense guns, and absolutely none of the thousands of infantry support weapons, (light machine guns to 150mm howitzers) had been destroyed. Clearly disposition in the tunnels and nearby jungle had preserved them.

Throughout the last two years of the campaign, Rabaul’s troops subsisted on rations, dressed in uniforms, and used the equipment that had been stockpiled for future operations in the southern Solomons which never eventuated, as well material intended for eastern New Guinea. When supplies ran short—which was frequent—the Japanese improvised. Daily field rations were supplemented by extensive vegetable gardens. More surprisingly, factories were built which turned out black powder and sulfuric acid for explosives, built home-made flame throwers and mortars, fabricated about 100,000 antitank mines and fused some 30,000 bombs as antipersonnel mines.

On September 6, 1945, Imamura and Kusaka boarded Royal Navy carrier HMS Glory, standing off Rabaul, and surrendered the forces of the Eighth Area Army and the Southeast Area Fleet to General Vernon A. H. Sturdee, commanding the Australian First Army. They and their men accepted the Emperor’s surrender order without incident. After three years, Rabaul had finally fallen.

Morison summed up Rabaul’s strength:

Fortunate it was indeed that the Joint Chiefs of Staff never ordered the capture of Rabaul and that the by-passing strategy was employed instead. Tarawa, Iwo Jima and Okinawa would have faded to pale pink in comparison with the blood that would have flowed if the Allies had attempted an assault on Fortress Rabaul.

(Cross-posted at USNI blog)