Photograph of Army troops moving through the jungle on New Georgia

U.S. Army. Via Wikipedia

Much of the fighting of the Pacific War took place in jungles. Nowadays usually referred to as tropical rain forests, these are ecosystems whose climate is characterized by high temperatures and heavy rainfall with little seasonal variation in either. They are found near the equator in areas that generally lack monsoons. The term "jungle" is somewhat variable in usage. Some authors include monsoon forests with tropical rain forests as jungles, while others define jungle as the nearly impenetrable mass of shrubs and vines found around the edges of tropical rain forests.

Jungles were terrible places for both the Japanese and the Allies to live and fight. When temperatures rose above 100° and the humidity was near 100%, even the slightest exertion would rapidly lead to heat exhaustion. The constant moisture quickly corroded metal, rotted leather and cloth, and reduced the resistance of human skin to infection. It was almost impossible to live off the land, since edible crops or animals were rarely to be found. Giant insects and dangerous animals seemed to be everywhere. But the biggest challenge may have been the abundance of tropical diseases, some of which still have no names in Western medical lexicons.

The most troublesome tropical disease was malaria, which infected 80% of the soldiers of some U.S. units stationed in the South Pacific. The Japanese fought malaria with quinine seized from Java; the Americans used atabrine, a synthetic antimalarial drug. The best solution to malaria, from the Allied perspective, was the wonder pesticide DDT, which eliminated the carrier mosquitoes. After the war, DDT would drastically reduce malaria rates around the world, only to be abandoned as an environmental threat — after which malaria rates would rebound drastically.

Another danger in the jungle was the leech, a distant relative of the earthworm. Some species of jungle leech were parasitic, attaching themselves to soldiers at the first opportunity to obtain a blood meal. When pulled off by hand, the leech left a laceration that often contained part of the jaw parts of the leech. Such wounds rapidly became infected, producing ulcers known in Burm as "Naga sores". Soldiers were advised to apply a burning cigarette to the leech to get it to let go, but this may have caused the leech to regurgitate part of its stomach contents into the wound. The modern recommendation is to break the seal between the leech's oral disk and the skin with a fingernail (Siddell 2008).

Although all jungle was characterized by abundant vegetation and high rainfall, the underlying terrain was highly variable. In flat regions like most of Sumatra or the New Guinea coast, poor drainage produced vast swamps that multiplied the misery of the troops. Terrain suitable for airfield construction existed only where fossil riverbeds of sand or gravel washed down from higher terrain provided a more stable base. Such terrain was particularly suitable for the growth of kunai grass, which was both a useful marker and a noisome hindrance to development: The very tall leaves (up to 10 feet or 3 meters) had razor-sharp edges. Where drainage was better, as in the rougher terrain characterizing most of the Solomon Islands, the soil was laterite, a kind of heavily leached soil poor in clay that often made an acceptable base for construction. Jungle was also found overlying fossil coral reefs, which hindered entrenchment and whose rough surface quickly destroyed foot gear. Ironically, while fossil reefs were impervious to entrenching tools, they were riddled with caves that were excellent as the basis of more elaborate field works constructed using heavier equipment, and the Japanese built almost impenetrable fortifications in places like Biak and Peleliu.

Undisturbed rain forest had relatively little undergrowth due to the perpetual twilight under the canopy of the trees. Such a forest was relatively easy to move about in. However, disturbed rain forest (and almost all the rain forest the troops operated in had been disturbed, either by native peoples or by Western planters) let in enough light to produce massive undergrowth, including tropical vines, that greatly hindered movement. The machete, a cleaver knife that could cut through vegetation, became standard equipment. Early in the war, U.S. Marine units improvised machetes out of surplus officer's swords. Army units at Bougainville concluded that a patrol moving out of the perimeter could expect to move no more than 700 yards (640 meters) per hour.

Because of restricted visibility, jungle combat tended to be fought at short range, with small arms and hand grenades, with an unusually high risk of friendly fire. Tanks found their movements highly restricted, and artillery often had to fire at high angle from small jungle clearings where it could neither be properly dispersed nor easily concentrated. This assumes that the artillery could even find a target: For example, flash-spotting and sound-ranging for counterbattery fire were almost impossible.  On the other hand, natural materials for camoflage were abundant and easily used.

The worst jungles in the world may well be the jungles of the Solomon Islands and New Guinea — precisely the areas where the decisive South Pacific campaign was fought. Some islands, such as Ndeni in the Santa Cruz group, were plagued with local strains of malaria so virulent that attempts to establish bases there had to be abandoned.

The Japanese soldier acquired a reputation early in the war as the supreme jungle fighter. This was largely a myth. Japan is a temperate country, and the Japanese Army gave little thought to jungle warfare prior to 1941, focusing instead on subarctic operations against the traditional enemy, Russia. Jungle warfare doctrine and training were largely the product of the Jungle Warfare Unit set up on Formosa in January 1941. This unit was shaped largely by Tsuji Masanobu, a fanatical pan-Asian who gave little thought to the welfare of the common soldier. Early successes in Malaya, where the Japanese outmaneuvered the largely road-bound British Army via flanking movements through the jungle, helped create the myth, and it was reinforced by further Japanese successes throughout southeast Asia during the Centrifugal Offensive. However, these Japanese operations were relatively brief and were heavily supported by air and sea power. Japanese troops attempting to duplicate the successes of the Centrifugal Offensive on Guadalcanal impressed the Marines with their tenacity, but it became clear during the counteroffensive just how much the Japanese troops had suffered in the jungle. Although Japanese troops continued to show considerable skill at prolonged defense on jungle islands, the majority of Japanese casualties in these areas were from disease and starvation, with 17 and 18 Armies suffering particularly heavily.

For the most part, American troops dealt with the jungle by either avoiding it or by getting rid of it. Allied bombardments stripped large areas of their jungle cover, and American engineering units (such as the Seabees) showed great skill at clearing jungle for roads and other facilities, burning off kunai grass and other growth and making heavy use of crushed coral and Marston mat. Liberal use of DDT disposed of tropical disease vectors, greatly reducing the incidence of malaria and other tropical fevers. However, the jungle could not be avoided during combat operations, and Allied troops developed considerable skill at jungle fighting, even if they never entirely lost their fear of the jungle.

Commonwealth troops proved particularly adept at jungle fighting, which was ironic given Churchill's unskeptical acceptance of the myth of  Japanese jungle superiority. Many of the Commonwealth troops that fought in Burma were Indian or African troops native to the tropics. Slim ordered a jungle warfare training school set up for 14 Army, with an entire division (39 Indian) designated as a jungle warfare training division. Bergerud (1996) argues that the volunteer Australian troops that fought in New Guinea were the best infantry in the Pacific. There seems little doubt that, by 1945, the Allies had become as adept at jungle warfare as their Japanese opponents.


Allen (1984)

Bailey (2004)

Bergerud (1996)

"Colonel Tsuji of Malaya"  (accessed 29 December 2006)

Gailey (1991)

Siddell (2008; accessed 2014-3-28)

Valid HTML 4.01 Transitional