Relief and Drainage
4. PRECIPITATION. The depositing of moisture
(rain, mist, snow, sleet, hail) from the atmosphere upon
RELIEF is the term given to the differing areas of
the surface of the earth, expressed in kind and amount.
elevation and depression on the surface of the earth.
5. WIND. The movement of air within the
DRAINAGE refers to those areas of surface depression
atmosphere. It is expressed as strength (velocity) and
that serve as water runoffs or collection points, such as
direction.
marshes, swamps, streams, rivers, ponds, and lakes.
Knowledge of the general shape of the land is gained
6. PHASES OF THE MOON. Usually, phases of
through a detailed study of the relief and drainage
the moon are expressed in quarters. The first quarter is
features. The steepness of slopes; the height and size of
between the new moon and the full moon; the second,
hill masses; the depth, the width, and the length of
or last quarter, between the full moon and the new moon.
drainage features; and the sizes of valleys and draws are
The two phases have a direct bearing on night visibility
major features to consider when studying the terrain of
and the amount of rise and frill of the tides.
a given area. These irregularities in the surface of the
earth influence tactics by the degree of observation they
The Effect of Weather on Tactics
provide the opposing forces, the ease or difficulty of
movement, and the degree of protection provided
Weather has a direct effect on the visibility, the
against enemy fire. Flat ground provides equal
movement, and the use and effect of weapons.
observation for the opposing forces; normally, high
Horizontal visibility may be materially reduced
ground in rolling or mountainous terrain provides for
(resulting in reducing the observation of the enemy or
better observation.
the effect of your fire on them) by fog, haze, heat
Any advances made parallel to a series of ridges or
refraction, or precipitation. Vertical visibility may be
to a river or stream are mechanically easier than
restricted by fog, precipitation, or a large mass of
movement perpendicular to them. The steepness of a
low-lying clouds, thus reducing the effectiveness of air
slope may limit movement; tanks, for instance, cannot
support or aerial reconnaissance. Ease of movement,
climb slopes greater than 30 degrees.
both logistical and tactical, on roads or cross-country
may vary drastically from day to day because of
Flat ground offers little protection against enemy
precipitation and temperature changes. A heavy rain
fire, but rolling ground will, particularly against
may change a passable area into an impassable
flat-trajectory weapons.
quagmire; but a severe temperature drop may cause the
Vegetation
same quagmire to frieeze, thus aiding movement.
Weather affects weapons, both in employment and
Vegetation is classified for practical purposes as
in the effectiveness of the weapon itself. The trajectory
either NATURAL or CULTIVATED. Natural plant life
of artillery and mortar rounds is greatly influenced by
includes all types of grasses, bushes, and trees growing
temperature and humidity. Extreme cold and hot
without the assistance of man; cultivated vegetation
weather require special treatment and handling of
includes all crops and orchards tended by man. Density,
gasoline engines, thus affecting the use of equipment
height, and types of growth, as well as the diameter of
and vehicles. The effects of weather are particularly
tree trunks, are significant features when you are
noticeable in air and naval weapon systems support. Air
studying vegetation.
support may be restricted or prevented entirely by
Although vegetation may restrict vision, it offers
clouds, fog, or heavy precipitation. Fog, snow, or heavy
concealment and limited cover. Of course, the thicker
rainfall reduce visibility; therefore, naval gunfire
the growth, the harder it is for the forces to move about.
support cannot be delivered as effectively, and new
targets cannot be rapidly located and engaged.
Surface Materials
TOPOGRAPHY
Surface materials are studied to determine the
trafficability of an area. "Trafficability" is defined as the
ability of a soil in its normal state to support vehicular
Topography consists of the physical aspects of the
traffic moving cross-country or on unimproved roads
surface of the earth and includes such features as relief
and trails. In general, all types of soil, except very loose
and drainage, vegetation, surface materials, and cultural
sand, afford good trafficability when dry. However, soils
features.
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