5-7. Effects of Environment
a. General. Basically, mapreading, as well as navigation under cold weather conditions, follows the same principles as in the temperate zones. In addition to the normal procedures, every individual must be most familiar with certain conditions peculiar to the cold weather regions and the techniques applicable to navigation. Due to the fact that a technical failure or human error may easily, and especially in the winter, be fatal to the individual or to a unit, great care must be exercised when navigating in low temperatures.
b. Navigation Problems. The following conditions, characteristic of the cold weather regions, will make accurate navigation very difficult:
(1) Lack of adequate large scale maps in the sparsely populated areas which will increase the requirements for and the use of aerial photographs.
(2) Photos of many areas will be difficult to read and interpret because of the absence of relief and contrast, and absence of manmade works for use as reference points.
(3) Dense forests and wildernesses offer few landmarks and limit visibility. Also, barren, monotonous tundra areas north of the tree line are characterized by lack of landmarks as aids for navigation.
(4) In winter, short daylight, fogs, snowfall, blizzards, drifting snow, especially in the barren areas, drastically limit visibility. At times an overcast sky and snow-covered terrain create a phenomenon called whiteout which makes recognition of irregularities in terrain extremely difficult.
(5) Heavy snow may completely obliterate existing tracks, trails, outlines of small lakes, and similar landmarks. Because the appearance of the terrain is quite different in winter from that in summer, particular attention must be paid to identifying landmarks, both on the ground and in aerial photos.
(6) Magnetic disturbances are encountered, making magnetic compass readings difficult and sometimes unreliable.
(7) Magnetic declination in different localities varies considerably, and must be taken into consideration when transposing from a map to a compass.
(8) Handling maps, compass, and other navigation instruments in low temperatures with bare hands is difficult. Removing handgear may often be possible for a very short period of time only.
5-8. Methods of Land Navigation
a. The normal methods of land navigation under cold weather conditions remain the same as anywhere else. Maps and aerial photos may be used alone during daylight in terrain which offers enough distinctive terrain features to serve as useful landmarks. They may also be used in conjunction with a compass, especially in terrain which contains insufficient landmarks or under circumstances when visibility is limited. However, in most instances, utilizing the map and compass together will provide for the surest land navigation in northern areas of operation.
b. Depending on various conditions, certain supplementary methods, such as position of the sun in daytime, North Star and Big Dipper at night, as described in FM 21-26, may be used to aid in land navigation. Where possible, these methods should be employed in conjunction with the normal methods described above.
c. It is obvious that on vast barren grounds as well as in wide forest, navigation by dead reckoning often becomes the only practical method. Dead reckoning is the process by which position at any instant is found by applying to the last determined position the direction and distance of the course traveled. This method should also be used in areas where landmarks are very limited or totally nonexistent. It is also desirable when the landmarks are obliterated by the limited visibility.
5-9. Navigation by Dead Reckoning
Navigation by dead reckoning is performed in accordance with FM 21-26. Due to the peculiarities of the cold weather regions, the following hints should be observed when applicable:
a. Responsibility for navigation is assigned to a detail of one officer or noncommissioned officer and 1 to 2 men, all thoroughly experienced in navigation techniques. The detail is placed directly under the control of the unit commander and must be released from the carrying of individual heavy loads and from details such as trailbreaking in order to perform their duties properly. Using a small detail rather than a single navigator is based upon the fact that the method of pacing distances in deep snow has to be modified as described in c below.
b. In general, the navigation detail is responsible for--
(1) Accumulating necessary instruments and equipment.
(2) Keeping instruments and equipment serviceable.
(3) Performing the detailed duties of taking and recording necessary data for precise location at all times.
(4) Maintaining liaison with the commander of the unit.
(5) Supplying data to keep the column on course.
c. Due to the sliding capacity of the skis, normal pacing system is very inaccurate or, in certain cases, such as on steep slopes, entirely useless. Pacing on snowshoes can be done in emergency. It must be borne in mind, however, that an individual mounted on snowshoes takes much shorter paces than on foot. The only recommended method for accurate ground measurements is a piece of line or field wire preferably 50 meters long (50 yds) used by two navigators.
d. Keeping a log is mandatory. The preparation of the log, as well as plotting the route from the log data on the face of the map or on a separate piece of paper at the same scale as the map, must be completed prior to the departure to minimize the use of instruments and equipment in low temperatures with bare hands.
e. Certain mechanized aids are highly valuable for navigation by dead reckoning.
(1) A magnetic compass has been developed for mounting in all vehicles.
(2) Odograph M1 is an instrument which automatically plots the course of a moving vehicle. It consists of three principal units--the compass; the plotting unit; and the powerpack. All components are interconnected by electric cable and flexible shafts. It was originally designed for use in the ¼-ton truck, but can be used in other vehicles to include track-laying vehicles and sleds for operation under winter conditions.
(3) Odograph M2 is much more accurate and convenient to use than the M1. It utilizes the miniature gyro-compass for the input of direction. In normal operations, if the map coordinates of the starting point are set on the instrument, it will provide the true coordinates of any point along the course of travel.
(4) The use of rotary wing aircraft for "pathfinding" in bush country greatly assists in land navigation. From the tactical point of view, however, it is less feasible because it tends to disclose the movement. Troops can reveal their position to the aircraft by the use of colored smoke. The pilot can then give them their position location by radio or dropped message.
