The Hollandia Area and The Terrain

The Allied organizations which were to move against the Hollandia area were to find there an excellent site for a major air and supply base, including the only good anchorage between Wewak in Australian New Guinea and Geelvink Bay, 450 miles northwest in Dutch New Guinea.5 The coast line in the Hollandia area is broken by Humboldt and Tanahmerah Bays, which lie about twenty-five miles apart. Between the two are the Cyclops Mountains, dominating the area. This short range rises to a height of over 7,000 feet and drops steeply to the Pacific Ocean on its northern side. South of the mountains is Lake Sentani, an irregularly crescent-shaped body of fresh water about fifteen and a half miles long. Between the north shore of the lake and the Cyclops Mountains is a flat plain well suited to airdrome construction, while other airfield sites are to be found on coastal flatlands just east of Humboldt Bay. South of Lake Sentani are more plains, which give way to rolling hills and a largely unexplored mountain range running roughly parallel to the coast about thirty or forty miles inland.
Hollandia is a wet area. In the Humboldt Bay region the average annual rainfall is 90-100 inches; around Tanahmerah Bay 130-140 inches; and in the Lake Sentani depression 60-70 inches. April is neither the wettest nor the driest month--those distinctions are reserved to February and September, respectively. But rain and mud can be anticipated at Hollandia during April, when the average rainfall is eight and one-half inches and about thirteen rainy days are to be expected. The rivers in the area flood after heavy rains, but flood conditions usually last only a few hours.
The Hollandia region was well suited for defense. The Cyclops Mountains presented an almost impassable barrier on the north while the width of New Guinea, with its rugged inland mountain chains, prevented an approach from the south. Movement of large bodies of troops along the coast either east or west of Hollandia was nearly impossible. Thus, the only practical means of access to the most important military objective in the area, the Lake Sentani Plain, was by amphibious assault at Humboldt Bay, on the east, or Tanahmerah Bay, on the west. From these two bays Lake Sentani could be approached only over many hills and through numerous defiles. Roads inland through these approaches were little better than foot trails prior to the war, but it was believed that they had been somewhat improved by the Japanese.
Landing beaches were numerous in the Humboldt Bay area, but there were few along the shores of Tanahmerah Bay. Almost all beaches in the region were narrow, backed by dense mangrove swamps, and easily defensible from hills to their rear and flanks. Measured by standards of jungle warfare, the distances from the beaches to the center of the Lake Sentani Plain were long, being eighteen miles by trail from Humboldt Bay and about fourteen miles from Tanahmerah Bay.
Japanese Developments at Hollandia
Hollandia had little claim to prominence before the war. Once it had been a center of trade in bird-of-paradise feathers, but this commerce had declined after 1931. In the late 1920's and early 1930's the Netherlands East Indies Government had promoted colonization and agriculture in the area, but labor trouble and sickness had caused these ventures to be practically abandoned by 1938. The town of Hollandia, situated on an arm of Humboldt Bay, then ceased to be commercially important and served only as the seat of local government and as a base for several exploring expeditions into the interior of Dutch New Guinea.
The Japanese occupied the Hollandia area early in April 1942 but paid little attention to the region until almost a year later, when Allied air reconnaissance disclosed that the enemy was constructing airfields on the Lake Sentani Plain. This development progressed slowly until late 1943, by which time successive reverses in the air and on the ground in eastern New Guinea and the Bismarck Archipelago, together with increasing shipping losses in the same region, began to demonstrate to the Japanese the vulnerability of their air and supply bases east of Hollandia.6 In late 1943 and early 1944 the enemy built three airfields on the Lake Sentani Plain and started a fourth at Tami, on the seacoast east of Humboldt Bay. Their reverses in eastern New Guinea prompted the Japanese to withdraw their strategic main line of resistance to the west, and the Hollandia airdromes were developed as the forward anchor of a string of air bases stretching from the southern Netherlands East Indies into the Philippine Islands. The Japanese 4th Air Army, principal enemy air headquarters in New Guinea, established at Hollandia an air base which ultimately became so large that it was surpassed in size and strength only by the air center earlier developed by the Japanese at Rabaul. At Hollandia the 4th Air Army and its operating echelon, the 6th Air Division, felt comparatively safe, for prior to 1944 that area lay beyond the effective range of Allied land-based fighter planes.
In addition, because of shipping losses east of Hollandia, the Japanese began to develop Humboldt Bay into a major supply base and transshipment point. Large ships would unload at Hollandia, whence cargo would be carried by barge to points southeast along the coast of New Guinea as far as Wewak, 215 miles away. Much of the cargo of the large ships remained at Hollandia to build up the base there. Continuous Japanese shipping activity throughout western New Guinea indicated to General MacArthur's Intelligence (G-2) Section that reinforcements were pouring into that area--reinforcements which might reach Hollandia. At the same time, it seemed possible that the Japanese 18th Army might send reinforcements to Hollandia from eastern New Guinea. Time favored whatever development the Japanese were undertaking at Hollandia. It was highly important that the Allies seize the area before the enemy could build it into a formidable fortress.7

The Decision to Take Aitape
Preliminary planning for an advance to Hollandia had been undertaken in General Headquarters during late February 1944. On 3 March representatives from major commands in both the South and Southwest Pacific Areas gathered at General MacArthur's command post in Brisbane, Australia, to discuss the problems involved in carrying out the direct advance to Hollandia without seizing an intermediate base in the Hansa Bay-Wewak area. It was immediately apparent to the Brisbane conferees that the basic problem was that of obtaining air support.
Obtaining Carrier-Based Air Support
Previous operations in the Southwest Pacific Area had been undertaken within effective range of Allied land-based fighter cover, but Hollandia was beyond this range, since the nearest Allied base was Nadzab in Australian New Guinea, almost 500 miles southeast of the objective. On the other hand, the Japanese had completed one airfield and were constructing two others in the Wakde Island-Sarmi area of Dutch New Guinea, only 125 miles northwest of Hollandia. Neither the Wakde-Sarmi nor the Hollandia fields could be kept neutralized by long-range bomber action alone. Fighter sweeps against both objectives would be necessary before D Day at Hollandia.
Since land-based fighters could not accomplish these tasks, the long jump to Hollandia could be undertaken only if carrier-borne air support could be obtained. The Southwest Pacific's naval arm had no carriers permanently assigned to it. Therefore, carriers had to be obtained from sources outside the theater.
In their 12 March directive the Joint Chiefs had instructed Admiral Nimitz to provide support for the Hollandia operation. Now, in accordance with these instructions, Admiral Nimitz proposed that he provide air support for Hollandia by undertaking carrier-based air strikes against Wakde-Sarmi and Hollandia prior to D Day. In addition, he would provide air support for the landings and, for a limited period thereafter, operations ashore. This support was to be made available by two groups of fast carriers assigned to Task Force 58 of the U.S. Fifth Fleet, an operational part of Admiral Nimitz' Pacific Fleet.
Initially, General MacArthur planned to have these carriers conduct fighter sweeps against Hollandia and the Wakde-Sarmi area on D minus 1 and D Day of the Hollandia operation. On D Day carriers would support the landings at Hollandia and then would remain in the objective area to furnish cover for ground operations and unloading of supplies and troops through D plus 8 or until fields for land-based fighters could be constructed at Hollandia. This plan was opposed by Admiral Nimitz on the grounds that it would invite disaster. In western New Guinea the Japanese were building many new airfields to which they could send large numbers of planes from other parts of the Netherlands East Indies or from the Philippines. There was no assurance that Allied carrier-based aircraft and land-based bombers could keep these enemy fields sufficiently neutralized to prevent the Japanese from staging large-scale air attacks against the Hollandia area. Admiral Nimitz therefore refused to leave the large carriers in the objective area for the period desired by the Southwest Pacific Area. Instead, he would permit Task Force 58 to remain in the Hollandia region only through D plus 3. General MacArthur reluctantly accepted this condition, although it left unsolved the problem of obtaining air support at Hollandia from D plus 3 until land-based fighters could be sent there. Many solutions were proposed for this problem.
Land-Based Air Support
General Headquarters, Southwest Pacific Area, had once given serious consideration to a plan to drop parachute troops on the Japanese-held airfields north of Lake Sentani. Since a large Japanese force was estimated to be defending Hollandia, there was no assurance that this action would be tactically successful. Even if the paratroopers captured the airfields quickly, there could be no assurance that enough men and engineering equipment could be flown to the Lake Sentani Plain in time to construct a fighter strip there before Task Force 58 was scheduled to retire. This plan was therefore abandoned
The Allied Air Forces proposed the establishment of land-based fighters on Wuvulu Island, which lies about 125 miles northeast of Hollandia. This plan was also given up. Little was known about terrain conditions on Wuvulu, the island was much closer to Japanese bases than to Allied, and its seizure would disclose the direction of the main attack. Furthermore, the Wuvulu operation would absorb ground forces, amphibious shipping, and engineering equipment sorely needed for the Hollandia campaign.
A plan to develop a fighter strip at Tanahmerah (inland in south-central Dutch New Guinea and not to be confused with Tanahmerah Bay) was likewise proposed and discarded. The terrain at the inland Tanahmerah was poor and the transportation of supplies and engineering equipment to the site would present major problems. Since Tanahmerah lies south and Hollandia north of the great unexplored inland mountain range which laterally bisects New Guinea, bad weather over this range, by no means unusual, might prevent fighters based at Tanahmerah from supporting landings at Hollandia. Also given serious consideration was the possibility of seizing a field in the Wakde-Sarmi area simultaneously with Hollandia. The principal obstacle to the execution of this plan was lack of sufficient assault shipping and landing craft to insure tactical success. Information about the Wakde-Sarmi area was exceedingly meager, but it was estimated by General MacArthur's G-2 Section that enemy strength there was growing rapidly.
It was finally decided to obtain land-based air support for Hollandia by seizing an airfield site on the northern New Guinea coast east of the main objective. The location chosen was a lightly held area already partially developed by the Japanese near Aitape, which lies in Australian New Guinea about 125 miles east-southeast of Hollandia.
The Aitape Area
Aitape had been occupied by the enemy in December 1942. Before the war the town was the seat of local government and an interisland trading point of but small commerce. The entire region is a coastal plain, varying from five to twelve miles in width, swampy in many places and cut by numerous streams. The only prominent terrain feature on the coast is a small hill at Aitape. There are no natural eastern or western boundaries in the area. To the north lies the Pacific Ocean, and south of the coastal plain rise the foothills of the Torricelli Mountains. Offshore, about eight miles east of Aitape, are four small islands. Good landing beaches exist throughout the region, the best a few miles east of Aitape. The absence of suitable terrain features makes difficult the defense of the area against amphibious assault. The many rivers could provide some defense against lateral movement, but these rivers vary greatly in width and depth according to the amount of rainfall.
April marks the end of the wettest season in the Aitape region, where rainfall averages about 100 inches per year. Though June is one of the dryest months, July is one of the wettest, with almost eight inches of rain. Torrential tropical downpours rather than prolonged rains are to be expected at Aitape.
Japanese development in the area centered around airfield construction near Tadji Plantation, about eight miles east-southeast of Aitape. At least three fields were begun by the enemy near Tadji at one time or another, but terrain conditions and lack of equipment prevented the Japanese from completing more than one of these strips. They used this field as a staging area for aircraft flying between Wewak and Hollandia and as a dispersal field for planes evacuated from heavily bombed airdromes east of Aitape. Intelligence reports indicated that Japanese ground defenses in the Aitape area were weak. It therefore seemed probable that there would be little opposition to a landing and that the assault force, once ashore, could quickly seize the airstrip area. It was estimated that Allied engineers could rehabilitate one of the Tadji strips for the use of fighter planes within forty-eight hours after the initial landings. Aircraft based on the Tadji strips would be within easy supporting distance of Hollandia, able to provide air cover after the carriers departed from Hollandia
The seizure of the Aitape area had an additional important aspect besides providing land-based support for Hollandia. Once established ashore at Aitape, Allied forces could provide ground flank protection for Hollandia against any westward movement on the part of the Japanese 18th Army.
Additional Air Support Problems
Although the decision to seize the Tadji airstrips assured that the departure of Task Force 58 would not leave ground operations at Hollandia without air support, other air support problems arose. The seizure of the Aitape area itself required air support, but Aitape, like Hollandia, was beyond the most effective range of Allied land-based fighters. Not enough large carriers had been made available to support the Hollandia landings (providing support for operations there for a few days and carrying out air strikes against Japanese bases in western New Guinea) and also to support the landing at Aitape.
Eight escort carriers (CVE's), together with the large carriers, had been made available by Admiral Nimitz to support the Hollandia operation. At first General MacArthur planned to use the escort carriers for close support missions at both Hollandia and Aitape, but it was decided that Task Force 58's carriers could provide all the air support necessary in the Hollandia area. Therefore the eight CVE's were to be used to support only the assault at Aitape and to cover ground operations in that area until one of the Tadji strips could be rehabilitated. They were to be released for return to the Central Pacific Area no later than D plus 19 of the Hollandia and Aitape landings, and earlier if possible.
In order to carry out all the air support missions which might become necessary, it was extremely important that the maximum possible number of fighters be based on the Tadji strips at an early date. Originally it was planned to send one fighter group of the U.S. Fifth Air Force to Tadji, a group containing both P-38 and P-40 aircraft; but it was expected that the airstrips, if in operation by D plus 1, would be rough and lacking many normal airfield facilities. It was therefore decided to send No. 78 Wing of the Royal Australian Air Force to Tadji. This Australian unit, which was comparable in size to an American group, was equipped solely with P-40 aircraft, planes peculiarly suited to operations under the rough conditions and incomplete facilities that could be expected at Tadji.