The Pacific War Online Encyclopedia
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U.S. Marine Corps. Via ibiblio.org
Military operations have always been strongly affected by the terrain of the battlefield, which affects movement and provides cover.
Movement. Flat, firm ground favors rapid movement by men and vehicles. However, in the presence of even modest rainfall, heavy military traffic could quickly pound seemingly substantial terrain into nearly impassable mud. Thus, engineers were required to build roads that could take heavy traffic. Where gravel and construction equipment was available, macadam roads could be constructed. At other locations, corduroy roads could be built from local timber, though this was an unpleasant surface for vehicular movement. United States engineers often made use of Marston mat to rapidly construct roads under less than ideal conditions.
required large areas of flat, firm
terrain and were built in essentially the same way as roads. Suitable
terrain for airfields was precious enough that entire campaigns were
fought for it. In New Guinea,
the Allies discovered that
ancient river beds, whose accumulated gravel provided a suitable base
for airfield construction, were often marked by fields of kunai grass.
In the equatorial jungles of the South Pacific, flat ground often lacked sufficient drainage to shed the torrential rainfall, which turned the terrain into swamps. Swamps were impassable to any kind of vehicle and all but impassable to men on foot. Relatively solid paths through swamps became killing grounds, as an advance was channeled along the paths and subject to heavy fire from defenders who were acquainted with the terrain.
Marine command post taking cover in gully. Via ibiblio.org
Vegetation provided much of the cover in the South Pacific and
elsewhere, but the underlying terrain was also critical. Possession of
the high ground favored both
attackers and defenders, as troops could
move behind a crest line unobserved. In
addition, some kinds of terrain were more favorable to entrenchment
than others. Entrenchment was all but impossible in either waterlogged
terrain, where the water table was struck just below the surface, or in
rocky terrain such as the fossil coral reefs
found at Peleliu and other
the other hand, fossil coral with its many caves was ideal for
construction of prepared positions using explosives and heavy equipment.
Effects on combat.
In general, rugged terrain favors the defense. Even under the best of
conditions, an attacker was reckoned to need a fire superiority of
three to one to overcome the natural advantages of the defender, whose
men could take maximum advantage of any available cover and whose heavy
weapons could be predeployed with maximum fields of fire. Thus an
attacker needed to be able to concentrate his forces faster than the
defender. An attack was a race to break through the defender's lines
before the defender could bring up reserves to reduce the
attacker's fire superiority to an ineffective level.
Rough terrain usually favors the defender in this race, who is able to bring up forces along routes that are not under enemy observation, while the attacker must frequently break cover to sustain his attack. However, skilled commanders were sometimes able to take advantage of terrain while attacking, particularly against inept defenders, as was the case for the Japanese in Malaya. The poorly-trained Allied troops were very reluctant to move off the established highways into the jungle, which allowed the Japanese to infiltrate through cover and surround Allied units before the Allies knew they were there.
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