Though the exposure of confidential deliberations among high-ranking civilian officials was a boon, providing a glimpse into Tokyo’s strategic plans for adding to the empire’s territorial holdings, the real prize was the Japanese military codes. Grotjan and other analysts attacked them with equal vigor, making inroads shortly after the war began, particularly against JN-25, the enciphering system widely used across the Imperial Japanese Navy.
Such breakthroughs would have a seismic impact. In April 1942, American forces were reeling across the Pacific when decoded intercepts pointed to a brewing campaign targeting Port Moresby, an Allied base on the southwest coast of New Guinea, just 300 miles from Australia. The Japanese already had footholds on both New Guinea and nearby New Britain, intending to use the two islands as a bulwark to protect the southern rim of their empire. The lure of Port Moresby was its airfield, from where Japanese bombers could reach Darwin, a major Allied port in northern Australia, and disrupt the shipping lanes connecting the United States to Australia and New Zealand.
It was a significant threat, not just to Australia and its seven million inhabitants, but to the long-range plans of US General Douglas MacArthur. Shortly after his arrival in Australia from the Philippines in March 1942, MacArthur was named commander-in-chief of all Allied ground, naval, and air forces in the Southwest Pacific Area. He intended to use the continent as his base of operations and a future springboard for a counteroffensive to the north.
MacArthur had vowed to return to the Philippines, deeply stung by his forced evacuation from Corregidor and the subsequent American surrender there. His first task was to amass men and materiel for such a campaign, but Admiral Chester W. Nimitz, commanding US forces in the adjoining theater, was clamoring for resources as well, and American factories and shipyards were still ramping up production, with hundreds of thousands of inductees awaiting training. That left MacArthur with limited means to block the expected Japanese thrust toward Port Moresby. He nonetheless plotted to turn the tables on his overstretched adversary, reclaim New Guinea and New Britain, and ultimately pivot north, where millions of Filipinos awaited liberation.
It would not be easy. A confident, experienced Japanese military held nearly every material advantage in 1942, but the ability of Allied intelligence to tap into Japanese communications more than evened the odds. That would soon be evident in the waters separating Australia from New Guinea, known as the Coral Sea.
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New Guinea, the second largest island in the world, featured some of the most rugged, unforgiving terrain in the Pacific. Measuring nearly 1,500 miles from end to end, or roughly the distance from Boston to Miami, it was completely roadless, and the island’s mountainous interior fed a network of meandering streams that could become torrents of water in the rainy season. Inland areas absorbed up to 300 inches of rain a year, leaving much of the landscape carpeted with lush jungles and mangrove swamps and producing a damp, oppressive environment with suffocating humidity and tropical heat.
A panoply of jungle diseases also flourished on New Guinea, including malaria, dysentery, and dengue fever. Ants, fleas, and spiders were everywhere, and future combatants on both sides would contract tropical ulcers—painful skin lesions—across their limbs and torsos, better known as “jungle rot.” In time, New Guinea became a cursed den of misery to every soldier who fought there.
The island comprised three distinct territories. Western New Guinea was part of the Dutch East Indies, while northeastern New Guinea, a former German colony, was a self-governing Australian mandate, awarded to Australia at the close of the First World War. Southeastern New Guinea, annexed by Australia in the late 19th century, was known as Papua, and Port Moresby was its capital. Across a narrow strait was the island of New Britain, with the city of Rabaul perched on its eastern tip. Occupied early in the war by the Japanese, Rabaul had an immense, natural harbor and multiple airfields. With a garrison of 100,000 soldiers, it had become Japan’s preeminent air and naval base in the Pacific and anchored a formidable defensive belt in the south. Sandwiched between New Guinea and the Japanese-held Solomon Islands, Rabaul was also ringed by a network of neighboring island bases.
Battle of the Coral Sea
To capture Port Moresby, nestled along Papua’s southern coast, the Japanese planned to surprise the Allies with an amphibious landing led by two of their premier aircraft carriers, with a smaller aircraft carrier in support. There would be no surprise, however, as Allied codebreakers had learned of the operation well before it began. MacArthur could not intercede, lacking much of a naval force, but Nimitz, commanding the US Pacific Fleet, gambled with his limited assets, ordering two of his four prized aircraft carriers into the Coral Sea to thwart the Japanese invasion. The clash in May 1942 made immediate history, becoming the first naval battle ever fought entirely by air groups operating from ships never in sight of one another.
The outcome proved costly to both sides. The Americans lost one flattop, the venerable USS Lexington, while another, the USS Yorktown, suffered severe damage to its flight deck. For their part, US carrier planes sank the smallest of the Japanese aircraft carriers, but neither of the other two emerged unscathed. The Zuikaku lost much of its air group, and the Shōkaku was marred by bombs, leaving Japan without the services of either during the forthcoming Battle of Midway.
New Guinea: The Fight Begins
With their Coral Sea operation derailed, the Japanese drew up an alternative plan for Port Moresby. In July, Imperial Army troops landed at Buna, on New Guinea’s eastern shore, with orders to cross overland and assault the Allied base from the island interior. Some 14,000 men set out on a backbreaking march thru the steeply sloped, 13,000-foot Owen Stanley mountain range that divided Papua. As the Japanese trudged across a narrow, precarious mountain trail inhospitable to vehicles, they were met by pockets of resistance. They pushed back the overmatched Australians and eventually closed to within twenty miles of Port Moresby, where they were blocked by a wall of fresh Australian troops. Weeks passed as the two sides engaged in a punishing, back-and-forth duel, but the Japanese were at a greater disadvantage, fighting well beyond their supply lines. Exhausted and starving, they fought in desperation, even resorting to cannibalism and consuming the flesh of dead comrades and prisoners.
By that time, the Imperial Army was locked into another brawl with US Marines on Guadalcanal, 900 miles to the east in the Solomon Islands. Unwilling to divide reinforcements and provisions between two fronts, the Japanese halted the drive to Port Moresby, withdrawing what was left of their invasion force and ending any imminent threat to Australia.
With the Japanese on the retreat and Allied bases already established along Papua’s southeastern coast, MacArthur was itching to go on the offensive. In November 1942, he ordered two divisions—the battle-tested Australian 7th Infantry and the newly arrived American 32nd Infantry—to attack Gona and Buna, the main Japanese beachheads in northern Papua.
It was an inauspicious beginning for the 12,000 men of the 32nd Division. There were thousands of Japanese around Buna, firmly entrenched in bunkers fronted by treacherous, swamp-filled ground, and the Americans, fresh out of training, were entirely unprepared for such warfare. Malaria and other diseases spread through the ranks, felling thousands of men, and poor leadership and rampant supply shortages compounded the woes. Only weeks into the operation, the division was in paralysis, plagued by disease, malnourishment, and plummeting morale. MacArthur, engaged by the widespread ineptitude and dereliction, ordered the three-star general in command of his ground forces to take personal charge of revitalizing the division.
The changes were swift. Officers were relieved, the division was restocked with replacement troops, tanks, medicine, and other supplies, and the men melded back into fighting shape. The Japanese, wilted by hunger and illness, were unable to withstand the renewed push, and by the end of 1942, most of the Japanese beachheads and perimeter were in Allied hands. An estimated 13,000 Imperial Army troops died in Papua, and though the Allies suffered far fewer casualties—an estimated 3,000 were killed—the 18,000 cases of malaria were an early lesson about the imperative of caring for troops in such harsh conditions.
The Allied Offensive
Despite the eventual loss of both Papua and Guadalcanal, the Japanese still wielded considerable strength in the theater and continued to hold out on New Guinea. In early 1943, they attempted to reinforce Lae, a key outpost in eastern New Guinea, but MacArthur was again tipped off by intelligence. His Fifth US Air Force sprang into action, pouncing on a Japanese convoy ferrying an entire division of 7,000 men across the straits from New Britain. The flotilla was ravaged, then attacked a second time the following morning, and what became known as the Battle of the Bismarck Sea ended in a lopsided Allied triumph, with eight transports and four of the escorting destroyers sent to the ocean bottom. Only a fraction of the troops reached New Guinea.
Weeks later, the Japanese suffered another dispiriting blow when a transport plane carrying Admiral Isoroku Yamamoto, commander in chief of the Japanese Combined Fleet and a national hero, was shot down by American fighter pilots in the Solomon Islands. The ambush, ordered after decoded intercepts revealed the iconic admiral’s flight plan, was a stunning blow to Japan and deprived the Imperial Navy of its most revered leader for the duration of the war.
By that time, American manufacturing was pouring new ships and aircraft into the Pacific, creating a widening divide in manpower, materiel, and technology, and leading to the launch of Operation CARTWHEEL. The long-anticipated counteroffensive was a sweeping, ambitious plan intended to isolate Rabaul, reduce its strength, and shatter Japanese defenses in the south. MacArthur was to advance up the coast of New Guinea, while Nimitz would push west across the Solomons, trapping the Japanese stronghold in a pincer between two powerful forces.
It started in June 1943 with MacArthur’s forces landing on the eastern tip of New Guinea. They drove up the coastline, battling assorted outposts supported by hundreds of bombers and fighter planes, but the Fifth US Air Force stepped in again. Despite persistent demands for new planes in the European Theater to support the strategic bombing campaign against Germany, MacArthur had managed to cobble together a potent air fleet in the southwest Pacific. Relying on planes largely unwanted in Europe, including P-40 Warhawks, P-38 Lightnings, and A-20 Havocs, American pilots began to dominate their matchups in the air. As the months passed, fewer and fewer Japanese pilots were left to contest the skies.
By September, US and Australian forces had captured the Japanese strongholds of Lae and Salamaua, followed by American soldiers and Marines wading ashore on western New Britain. They captured the Arawe Peninsula and Cape Gloucester, winning control of the straits between New Britain and New Guinea, and by February 1944, Nimitz had completed his drive across the Solomons, leaving Rabaul fully encircled.
At that point, US leaders saw little utility in sacrificing thousands of lives to wrestle the base away from such a massive garrison. Instead, Rabaul was bypassed, though air strikes would continue to whittle away any of its remaining offensive power. That freed Nimitz to pursue a new strategy. Armed with fresh divisions of soldiers and Marines and powerful new aircraft carriers and battleships, his forces began a concerted push in the Central Pacific, home to Japanese-held airstrips that could be converted to US air bases. That would position newly arrived B-29 long-range bombers within reach of the Japanese home islands.
Though MacArthur was as displeased by the decision to bypass Rabaul as he was with the spotlight shifting to Nimitz, he at least had approval to continue his march to the Philippines. He resumed his northward drive, eager to vanquish the Japanese in eastern and western New Guinea and use coastal bases and islands there as steppingstones to Philippine waters. He had no shortage of manpower, as ten American and Australian divisions were now under his fold, with three more divisions in transit from the United States. He also had ample air and naval support, with more than 1,000 bombers and fighters planes and enough naval transports and escort ships to safely land his army along the New Guinea coastline.
In April 1944, more intercepted messages—US forces had captured a bounty of Japanese codebooks—revealed a large concentration of enemy troops near Wewak and Hansa Bay, awaiting the next American landing. MacArthur detoured around them, sending his assault forces hundreds of miles up the coast to Hollandia, a major Japanese air and supply base in Dutch New Guinea. Masses of B-24 Liberators and long-range P-38 Lightning fighter planes delivered a pre-invasion drubbing, feasting on the aircraft sprinkled across Hollandia’s airfields and destroying more than 340 planes. It virtually wiped out Japanese air power on New Guinea and allowed a pair of US infantry divisions to land near Hollandia with relative ease. The sparse Japanese troops nearby fled into the adjoining jungle, leaving Hollandia in American hands and leapfrogged Imperial Army troops near Wewak and Hansa Bay cut off from retreat.
MacArthur’s forces continued their westward drive along the coast, battling remnants of defenders along a series of enclaves and islands just offshore. By late summer, most of New Guinea was under Allied control, including key bases scattered along the island’s far northwestern coast. That put MacArthur’s air forces within striking distance of Japanese outposts in the Philippines, and in October, the vanguard of his army arrived on the beaches of Leyte. That became the opening act of a months-long campaign to liberate and reclaim one of the most prized possessions in the Far East.
Aftermath
It had been a costly, painstaking journey across the South and Central Pacific, and for more than two years, American and Australian soldiers endured unimaginable hardships during their jungle combat on New Guinea. The island became as much of an enemy as the Japanese. Monsoon rains and ankle-deep and mud-filled trails and roads were among the horrors, as were constant sniper attacks, nighttime ambushes, disease, and utter exhaustion. Psychological trauma was also rampant, with scores of soldiers suffering neuropsychological breakdowns.
If the campaign was trying for the Allies, it was a catastrophe for the Japanese. Virtually an entire army was lost on New Guinea, and on New Britain, 100,000 soldiers and sailors at Rabaul were stranded and removed from the war entirely. The Allied triumph left MacArthur’s forces poised for a return to the Philippines, but the most formidable enemy force outside mainland Asia—nearly half a million men, supported by thousands of tanks and planes—awaited their arrival. In the end, MacArthur fulfilled his past promise, triumphantly returning to the beloved land and people he was so ardently attached to.
