The 'Campaign for Eastern Papua' was fought between the Allied and Japanese forces in the western coastal region of the large island of New Guinea (23 January 1942/16 April 1943).

During the campaign’s initial phase early in 1942, Japanese forces invaded the Territory of New Guinea on 23 January and the Territory of Papua on 21 July, and overran western New Guinea (part of the Netherlands East Indies) from on 29 March. During the second phase, lasting from late 1942 until the Japanese surrender, the Allied forces, composed largely of Australians together with significant numbers of Americans, cleared the Japanese first from Papua, then New Guinea and finally from the Dutch colony.

The campaign resulted in a crushing defeat and heavy losses for Japan: as in most Pacific War campaigns, disease and starvation claimed more Japanese lives than Allied action. Most Japanese troops never even came into contact with Allied forces and were instead simply cut off and subjected to an effective blockade by the Allied naval forces. Garrisons were effectively besieged and denied shipments of food and medical supplies, and as a result some claim that as much as 97% of Japanese deaths in this campaign were from non-combat causes.

The struggle for New Guinea began with the 'R' capture by the Japanese of Rabaul at the north-eastern tip of New Britain island during January 1942. Rabaul overlooks Simpson Harbour, a considerable natural anchorage in an area ideal for the construction of airfields. Over the next year, the Japanese built the area into a major air and naval base, and the Allies responded with several bombing raids on Rabaul as well as action off Bougainville.

The Japanese 8^th Area Army, under the command of Lieutenant General Hitoshi Imamura and based at Rabaul, was responsible for the campaigns in both New Guinea and the Solomon islands group, and the 18^th Army, under the command of Lieutenant General Hatazo Adachi, was responsible for Japanese operations on mainland New Guinea.

Port Moresby, on the southern coast of Papua and the Australian colonial capital, was the strategic key for the Japanese in this area of operations. The capture of Port Moresby would both neutralise the Allies' principal forward base and serve as a springboard for a possible invasion of Australia. For the same reasons, General Douglas MacArthur, commander of the Allied forces in the South-West Pacific Area, was determined to hold it. MacArthur was further determined to take all New Guinea in his progress toward the eventual recapture of the Philippine islands group. Operational Instruction No. 7, issued by the General Headquarters South-West Pacific Area on 25 May 1942, placed all Australian and US Army, US Army Air Force and US Navy forces in the Port Moresby Area under the control of New Guinea Force, itself commanded by Major General B. M. Morris, from August 1942 Lieutenant General S. F. Rowell and from September 1942 Lieutenant General E. F. Herring.

Directly to the north of Port Moresby, on the north-eastern coast of Papua, are the Huon Gulf and the Huon peninsula. The Japanese entered Lae and Salamaua, two towns on Huon Gulf, on 8 March 1942 in their 'Sr' undertaking and met no opposition. MacArthur would have preferred to deny this area to the Japanese, but he lacked the strength of both land and sea forces to undertake a counter-landing. The Japanese at Rabaul and other bases on New Britain would have easily overwhelmed any such effort. By the middle of September, MacArthur’s entire naval force, under the command of Rear Admiral Arthur S. Carpender, comprised five cruisers, eight destroyers, 20 submarines and seven small craft. The only Allied response was the bombing of Lae and Salamaua by aircraft flying over the Owen Stanley mountain range from the US fleet carriers Lexington and Yorktown: the only real result of the bombing was the Japanese decision to reinforce these sites.

'Mo' was the designation given by the Japanese to their initial plan to take Port Moresby. The operation’s plan decreed a five-pronged attack: one task force to establish a seaplane base at Tulagi island in the south-eastern end of the Solomon islands group, one to establish a seaplane base in the Louisiade archipelago off the eastern tip of New Guinea, one of vessels to transport and land troops near Port Moresby, one with a light carrier to provide air cover for the landing, and one with two fleet carriers to sink the Allied forces sent in response to the Japanese operation. In the resulting 'Battle of the Coral Sea' (4/8 May 1942), the Allies suffered higher losses in ships but achieved a crucial strategic victory by persuading the Japanese to recall their landing force, thereby removing the direct threat to Port Moresby, at least for the time being.

Following this failure, the Japanese decided on a longer-term, two-pronged assault for their next attempt on Port Moresby. Forward positions would first be established at Milne Bay, located in the forked eastern end of the Papuan peninsula, and at Buna and Gona, villages on the north-eastern coast of Papua about midway between the Huon Gulf and Milne Bay. Simultaneous operations from these two locations, one amphibious and one overland, would converge on Port Moresby.

Buna and Gona were easily taken as the Allies had no military presence there: MacArthur had sagely selected not to attempt an occupation by paratroopers since any such force would have been easily wiped out by the Japanese. In 'Ri', the Japanese occupied the villages with an initial force of 1,500 men on 21 July 1942 and by 22 August had 11,430 men under arms at Buna.

The Japanese objective was to seize Port Moresby by means of an overland advance from the north coast, following the Kokoda Track over the mountains of the Owen Stanley mountain range, as part of a strategy to isolate Australia from the USA. By 17 September the Japanese had reached the village of Ioribaiwa, just 18.5 miles (30 km) short of the Allied airfield at Port Moresby. The Australians held firm under the most arduous of operational and natural conditions, however, and began their counterdrive on 26 September. According to the US Navy’s official historian, '…the Japanese retreat down the Kokoda Track had turned into a rout. Thousands perished from starvation and disease; the commanding general, [Major General Tomitaro] Horii, was drowned.' Thus was the overland threat to Port Moresby permanently removed.

As Port Moresby was the only port supporting operations in Papua, its defence was critical to the campaign. The air defences consisted of Bell P-39 Airacobra and Curtiss P-40 Warhawk single-engined fighters. Royal Australian Air Force radar could not provide sufficient warning of Japanese attacks, so reliance was placed on coastwatchers and spotters in the hills until a US radar unit arrived in September with better equipment. Japanese bombers were often escorted by fighters and arrived at 30,000 ft (9145 m), which was too great an altitude for interception by the P-39 and P-40 fighters, giving the Japanese an altitude advantage in air combat. The cost to the Allied fighters was high: before June, between 20 and 25 P-39 fighters had been lost in air combat, while three more had been destroyed on the ground, and eight had been destroyed in landing accidents. In the following month at least 20 fighters were lost in combat, while eight were destroyed in July.

The Australian and US anti-aircraft gunners of the Composite Anti-Aircraft Defences played a crucial role in protecting Port Moresby, which had suffered 78 air raids by 17 August 1942. A gradual improvement the numbers and skill of anti-aircraft gunners forced the Japanese bombers up to higher altitude, where their bombing was less accurate, and then, in August, to raiding by night.

Although RAAF Consolidated PBY Catalina twin-engined flying boats and Lockheed Hudson twin-engined light bombers were based at Port Moresby, the Japanese air attacks meant that long-range bombers such as the Boeing B-17 four-engined heavy bomber, North American B-25 Mitchell twin-engined medium bomber and Martin B-26 Marauder twin-engined medium bomber could not be safely based there and were instead staged through from bases in Australia. This resulted in considerable fatigue for the air crews. As a result of USAAF doctrine and the lack of long-range escort fighters, long-range bomber raids on targets like Rabaul went in unescorted and suffered heavy losses, prompting severe criticism of Lieutenant General George H. Brett by war correspondents for misusing his forces. But fighters did provide cover for the transport aircraft and for the bombers when their targets were within range. Aircraft based at Port Moresby and Milne Bay fought to prevent the Japanese from basing aircraft at Buna, and attempted to prevent the Japanese reinforcement of the Buna area. As the Japanese ground forces pressed toward Port Moresby, the Allied air forces struck supply points along the Kokoda Track. Japanese makeshift bridges were attacked by P-40 fighter-bombers with 500-lb (227-kg) bombs.

While it was beyond MacArthur’s capabilities to deny Buna to the Japanese, the same could not be said of Milne Bay, which was easily accessible by Allied naval forces. Early in June, US Army engineers, Australian infantry and an anti-aircraft battery were landed at Gili Gili, and work on an airfield was started. By 22 August, about 8,500 Australians and 1,300 Americans were on site. The Japanese 'Re' assault arrived, from 25 August the 'Battle of Milne Bay' was fought, and by 7 September had been won by the Allies.

The D’Entrecasteaux islands group lies directly off the north-eastern coast of the lower portion of the Papuan peninsula. The westernmost island of this group, Goodenough, had been occupied in August 1942 by 353 stranded troops from bombed Japanese landing craft. The destroyer Yayoi, sent to recover these men, was bombed and sunk on 11 September. A force of 800 Australian troops landed on 22 October on either side of the Japanese position. Beleaguered, the survivors of the Japanese garrison were evacuated by submarine on the night of 26 October. The Allies proceeded to turn the island into an air base.

The Japanese attempt to take the whole of New Guinea had been decisively stopped. MacArthur was determined not just to halt the Japanese but then to liberate the island as a stepping-stone to the reconquest of the Philippine islands group, and began his strategic campaign on 16 November 1942. The inexperience of Major General Edwin F. Harding’s US 32^nd Division, just out of training camp and unschooled in jungle warfare, was nearly disastrous. Instances were noted of officers completely out of their depth, of men eating meals when they should have been on the firing line, even of cowardice. MacArthur replaced Harding with Lieutenant General Robert L. Eichelberger on 15 December after two interim commanders had been wounded, and on 30 November had already instructed this officer, who was also commander of the US I Corps, to go to the front personally with the order 'to remove all officers who won’t fight…if necessary, put sergeants in charge of battalions…I want you to take Buna, or not come back alive.'

The Australian 7^th Division, commanded by Major General G. A. Vasey, and the revitalised US 32^nd Division resumed the Allied offensive. Gona fell to the Australians on 9 December 1942, Buna to the US 32^nd Division on 2 January 1943, and Sanananda, located between the two larger villages, fell to the Australians on 22 January.

Between 18 December 1942 and June 1943, 'Lilliput' was an ongoing resupply operation to deliver troops and supplies from Milne Bay to Oro Bay, a little more than mid-way between Milne Bay and the Buna/Gona area.

Wau is a village in the interior of the Papuan peninsula, about 31 miles (50 km) to the south-west of Salamaua. An airfield had been built there during the area’s gold rush in the 1920s and 1930s, and this airfield came to be of great value to the Australians during the fighting for north-eastern Papua. Once the Japanese had decided to end their attempt to take and hold Guadalcanal, the capture of Port Moresby loomed even larger in their strategic thinking. Taking the airfield at Wau was a crucial step in this process, and to this end, Lieutenant General Hidemitsu Nakano’s 51^st Division was transferred from Indo-China and placed under Imamura’s 8^th Area Army at Rabaul. One of the division’s regiments arrived at Lae early in January 1943. In addition, about 5,400 survivors of the Japanese defeat at Buna and Gona were moved into the area of Lae and Salamaua. Opposing these forces were the Australian 2/5^th, 2/6^th and 2/7^th Battalions along with Lieutenant Colonel N. Fleay’s 'Kanga' Force. The Australians decisively beat the Japanese assault in the ensuing 'Battle of Wau' on 29/31 January 1943. About one week later, the Japanese completed their 'Ke' (i) evacuation of Guadalcanal.

Imamura and his naval counterpart at Rabaul, Vice Admiral Jinichi Kusaka, commander of the South-East Area Fleet, resolved to reinforce their ground forces at Lae for a final assault to take Wau. If the transport vessels succeeded in staying behind a weather front and were protected the whole way by fighters from the various airfields surrounding the Bismarck Sea, the Japanese command came to believe that they might reach Lae with an acceptable level of loss (the loss of only half of the task force). It is indicative of the extent to which Japanese ambitions had fallen at this point in the war that a 50% loss of ground troops aboard ship was considered acceptable.

A trio of factors combined to create disaster for the Japanese. Firstly, they had woefully underestimated the strength of the Allied air forces. Secondly, the Allies had become convinced that the Japanese were preparing a major seaborne reinforcement and so had stepped up their air searches. Thirdly and most importantly of all, the bombers of MacArthur’s air forces, under the command of Lieutenant General George C. Kenney, had been modified to enable new offensive tactics. The noses of several Douglas A-20 Havoc twin-engined light bombers had been refitted with eight 0.5-in (12.7-mm) machine guns for strafing slow-moving ships. In addition, their bomb bays were filled with 500-lb (227-kg) bombs to be used in the newly devised practice of skip bombing.

About 6,900 troops aboard eight transports, escorted by eight destroyers, departed Rabaul at 00.00 on 28 February under the command of Rear Admiral Masatomi Kimura. Through the afternoon of 1 March, the overcast weather continued, but at this point everything began to go wrong for the Japanese. The weather changed direction and Kimura’s slow-moving task force was spotted by an Allied reconnaissance aeroplane. By the time the Allied bombers and PT-boats finished their work on 3 March, Kimura had lost all eight transports and four of his eight destroyers in the 'Battle of the Bismarck Sea'. The remaining destroyers, carrying about 2,700 surviving troops, limped back to Rabaul and the Japanese never again risked a transport larger than a small coaster or barge in waters shadowed by US aircraft.

Admiral Isoroku Yamamoto, commander of the Combined Fleet, promised Emperor Hirohito that he would pay back the Allies for the disaster at the Bismarck Sea with a series of massive air attacks. For this, Yamamoto ordered the air arm of Vice Admiral Jisaburo Ozawa’s 3^rd Fleet carriers to reinforce the 11^th Air Fleet at Rabaul. To demonstrate the seriousness of the effort to the supreme war council, several changes of high-ranking personnel were also effected: both Yamamoto and Ozawa moved their headquarters to Rabaul, and Vice Admiral Gunichi Mikawa, the 8^th Fleet's commander, and Major General Rimpei Kato, the 8^th Area Army's chief-of-staff were sent to Tokyo with advice and explanations for the respective general staffs. Vice Admiral Baron Tomoshige Samejima replaced Mikawa as commander of the 8^th Fleet.

The resulting 'I' operation was to be carried out in two phases, one against the lower end of the Solomon islands group and the other against Papua. The first attack, on 7 April, was flown against Allied shipping in the waters between Guadalcanal and Tulagi. With 177 aircraft, this was the largest Japanese air attack since Pearl Harbor. Yamamoto then turned his attention to New Guinea, and 94 warplanes struck Oro Bay on 11 April, 174 aircraft hit Port Moresby on 12 April, and in the largest raid of all 188 aircraft struck Milne Bay on 14 April.

'I' clearly illustrated the fact that the Japanese command was not learning the lessons of air power that the Allies were learning and implementing. The Allied reduction of Rabaul was made possible only by relentless air attacks on a day-by-day basis, but Yamamoto thought the damage inflicted by a few attacks of large formations would derail Allied plans long enough for Japan to prepare a defence in depth. Also, Yamamoto accepted at face value his air crews' over-optimistic reports of damage: they reported a score of one cruiser, two destroyers and 25 transport vessels, as well as 175 Allied aircraft, figures which should certainly have aroused scepticism. Actual Allied losses amounted to one destroyer, one oiler, one corvette, two cargo ships and about 25 aircraft. The poverty of these results were in no way commensurate with either the resources expended or the expectations that had been raised.

In order to reduce and capture the very substantial Japanese naval and air facilities at Rabaul, two major moves were planned for the end of June: Rear Admiral Richmond K. Turner’s Task Force 31 undertook the 'Toenails' campaign on the New Georgia islands group’s midway up the chain of the Solomons islands group (30 June/7 October 1943); and Rear Admiral Daniel E. Barbey’s Task Force 76 carried out two back-to-back landings on the form of the 'Chronicle' seizure of the Trobriand islands group between Papua and the Solomon islands group (22/30 June 1943), and the landing of a combined US and Australian force at Nassau Bay on the Papuan coast just to the south of the Huon Gulf (30 June/6 July 1943).

Eventually, the Joint Chiefs-of-Staff realised that a landing and siege of 'Fortress Rabaul' would be far too costly and that the Allies' ultimate strategic purposes could be achieved by simply neutralising and bypassing it. At the 'Quadrant' conference in Quebec during August 1943, the leaders of the Allied nations agreed to this change in strategy as 'Cartwheel' focusing on the neutralisation rather than seizure of Rabaul.

Despite their disaster in the 'Battle of the Bismarck Sea', the Japanese could not forego the recapture of Wau, and this paved the way to the 'Campaign for Salamaua and Lae', which was the next step in the 'Campaign for New Guinea'.