c) Weather. The seasonal weather in the theater will have a direct
bearing upon operations. The use of aircraft, the employment of light
forces, the habitability of ships over long periods, the use of smoke,
the range at which a gun action may be fought, the effect of spray and
gases,--these considerations are but some of the matters which will be
affected by weather.

The possession of, and the position of, meteorological stations within
the theater are of growing importance in the successful planning of
coordinated air, submarine, and surface operations.

(d) Daylight and Dark Periods. It may be well under this heading to
put in tabular form the times of sunrise, sunset, moonrise, moonset,
the phases of the moon, and the duration of morning and evening
twilight. When, for example, the commander is considering night
destroyer attacks, the operation of submarines, or the type of
protective screens he desires to use, he may profitably refer to these
tabulations.

(e) Relative Location and Distance. No part of the study of the
characteristics of the theater is of greater importance than that
pertaining to relative location and distance. At this point it may be
found advantageous to place in tabular form the distances between the
important positions within the geographical area of the theater. This
study furnishes knowledge as to the availability of certain localities
for use in support of, or in cooperation with, forces at other
localities, and as to distances in relation to steaming capabilities
of the various units which make up the commander's force.

(f) Lines of Transportation and Supply. The usual sea routes which
pass through the theater are an important subject of study; also,
particular focal points, defiles, and restricted waters which are, or
may prove to be, critical areas with respect to own or enemy forces.
Other items are the significant routes from home or enemy territory,
i.e., the lines of communication, the terminal points, and the
flanking positions along these lines.

(g) Facilities and Fortifications. The facilities for the support,
upkeep, and repair of the units of the commander's forces and of the
opposing force, as well as the fortifications existing within the
area, may require consideration. Other features which may render a
port or base of value, or which may indicate a possible necessity of
denying it to the enemy, also merit attention.

(h) Communications. In strategical estimates, mo