Jungle

Much of the fighting of the Pacific War took place in jungles. Nowadays usually referred to as tropical rain forests, these are ecosystems 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 a variety of diseases. 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. Neither cured the disease once it was contracted, but they could help prevent infection and reduce the severity of symptoms. The best solution, from the Allied perspective, came with the introduction of 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 equally drastically.

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.

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.

References

Bergerud (1996)