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66. PURPOSE. The need for advanced landing fields becomes urgent as our troops move rapidly ahead or, in some cases, on islands or territory behind the enemy. Time is the all-important factor and this type field may serve its purpose if available for only a few days. As the forward area becomes the rear area, an advanced landing field can be improved for our medium and heavy bombers but initially it serves our fighter and transport planes.

67. REQUIREMENTS. a. Speed and simplicity are the essence of advanced landing field construction. Three essential factors govern speed of construction: reconnaissance to find a site at which little work is needed; getting troops, equipment, and material to the site quickly; and continuous work until the field is in operation. Simplicity means undertaking no more work than is necessary for immediate air operations.
  b. Dimensional and lay-out criteria for advanced landing fields are given in chapter 7. However, military necessity often requires deviation from recommended minimum standards, especially for the more temporary fields. The common deviations are steeper angle of glide and greater angular difference between direction of landing strip and prevailing wind direction.
  c. The minimum facilities to be provided at an advanced landing field usually are:
(1) One landing strip with dispersed hard standings and connecting taxiways, all cleared, drained, and graded. These must be surfaced if used for operations in wet weather (fig. 19(6)).
(2) An access road, unless air transport is used.
(3) Dumps for supplies, ammunition, and gasoline drums.
(4) Service roads from damps to taxiways and hard standings.
(5) Drinking water supply.
  d. To permit rapid construction a site must be fairly clear of trees and dense growth, flat enough to require little grading, and slightly sloped, so that effective drainage can be provided by simple open ditches.
  e. Because of their temporary nature and susceptibility to enemy raids provision must be made for continuous maintenance and repair (ch. 24).

68. RECONNAISSANCE AND LAY-OUT. a. The reconnaissance procedure for advanced landing fields, generally, is as described in chapter 8, with special emphasis on detailed study of aerial photographs, maps, and intelligence reports. All possible information should be compiled in advance of ground reconnaissance, sometimes even to the point of a preliminary lay-out. Ground reconnaissance upon arrival at the site must be a rapid but accurate appraisal of conditions, or verification of previously acquired information.
  b. A practical test for stability and wheel-supporting capacity of an earth surface may be made by running a car or truck back and forth over a short distance six times in the same tracks. If the resulting depression, measured at the midlength of the track, is no more than about one-half inch, and if no further deepening results with additional running in the same tracks, the surface is satisfactory.
  c. Lay-out is decided during the reconnaissance. Detailed surveys and plans are not made (fig. 24(1)). Usually a center-line profile and a few transverse profiles are taken from which the grade line is established and the drainage scheme decided. (See chs. 10 and 13.)
  d. If a base course is required, the reconnaissance must include location of suitable materials and decision as to the thickness and method of construction. (See chs. 11, 12, and 15.)

69. HASTY ESTIMATES. Quantities of work to be done are estimated from the plans formulated during reconnaissance. These quantities are the basis for estimating either the equipment and troops required to meet a specified completion date or the time required to do the job with the troops and equipment on hand. (See ch. 21 for methods of estimating, especially par. 169.)

70. DRY-WEATHER EARTH FIELDS (fig. 24). a. Soil. The character of soil on the landing-strip is the primary factor. Any soil is satisfactory if it can be stabilized easily and maintained in a firm condition suitable for plane operation. A well-graded soil containing coarse and fine particles is desirable because it can be stabilized readily by sprinkling and compaction. With good surface drainage it does not lose stability quickly in ordinary rains. Fine-grained soils are less desirable but will serve if they can be compacted. They lose stability quickly under rain, and during dry weather some types, such as silts with little cohesion, pulverize rapidly under traffic. Unsatisfactory soils are loose sand, cohesionless silt, and loose gravel. Often these can be made satisfactory by stabilizing processes discussed in paragraph 128, but considerable time is required for construction. Usually, laying a steel landing mat (ch. 16) is the quickest way of preparing such sites (fig. 26). (For complete discussion of soil classification and characteristics see ch. 11.)

Figure 24. Constructing compacted earth dry-weather advanced landing field.
(1) Start of work.
(1) Start of work.
(2) Grading.
(2) Grading.
(3) compacting with roller and trucks. Note corner marker of white stone rolled into surface.
(3) compacting with roller and trucks. Note corner marker of white stone rolled into surface.

  b. Construction (fig. 24). The usual procedure consists of clearing and grading, disking, sprinkling, and compacting. See chapter 13 for detailed explanation of these processes. Grading is limited to providing a longitudinal profile satisfactory for planes and a cross section that will drain the surface. Stones larger than about 2-inch diameter that are not embedded firmly in the surface must be removed from the landing strip. Slopes are difficult to judge by eye and in doubtful cases an engineer's level should be used. An ordinary clinometer is not sufficiently accurate. A practical test for smoothness of the surface may be made by driving a car over it at 20 and at 50 miles per hour. If there is no undue jarring or bumping, the surface is satisfactory.
  c. Maintenance. Earth surfaces require constant maintenance. The principal problems are dust from loosening of the surface and mud from rainstorms (figs. 107 and 25). To settle dust water-sprinkling and rolling are employed. Dust palliatives, discussed in chapter 17, also may be used. The best protection against mud is positive surface drainage and outfall discharge of collected surface water. (See ch. 24 for more detailed discussion of maintenance and repair procedures.)

71. ALL-WEATHER FIELDS. a. Drainage usually is the first and most important consideration for an all-weather field, both to preserve the strength of subgrade and base (par. 96) and to minimize the hazard to plane operations of standing surface water (fig. 25). Provision must be made for positive disposal of surface water by shaping the cross section to shed water to the sides (fig. 16). Open channels along the sides of the landing strip are provided to receive the surface water and carry it to a natural drainage channel or an outfall ditch away from the site (figs. 49 and 89). Every landing strip should be virtually an island surrounded by drainage channels carrying water away. (For design of drainage systems see ch. 13.) Wherever water may flow onto a site from adjoining ground it is necessary to construct intercepting ditches or dikes to collect and divert it from the landing strip (par. 117a). The ground-water level should be at least 2 feet below the low point of the subgrade. If the advanced landing field later is developed into a field airdrome for continuous operation, the subgrade should be 4 feet above ground-water level unless the soil is granular and unaffected by water. Where ground water is a consideration and the subgrade soil will respond to sub-drainage (table V) deep open ditches should be dug along the sides of the landing strip to lower and control the water level. Water collected by these side subdrains should be discharged through an outfall. When practicable, explosives should be used freely to permit rapid excavation of the side ditches and outfall.
  b. A steel landing mat usually is the fastest means of providing a surface for all-weather operations. It works well on subgrades or bases such as sand that do not soften appreciably when wet (fig. 26). In an emergency, it can be used for temporary operations on soils of low stability, but constant maintenance is required to keep the runway usable. If air operations must continue under such circumstances, a base course must be provided. (See par. 131 for design of the base.)

Figure 25. Surface water and mud are seriuos hazard to aircraft operation.
Figure 25. Surface water and mud are seriuos hazard to aircraft operation.

Figure 26. Steel landing mat works well on beach sand; however, for continuous operation sand should be treated (ch. 16) to prevent its displacement by propeller and exhaust blast.
Figure 26. Steel landing mat works well on beach sand; however, for continuous operation sand should be treated (ch. 16) to prevent its displacement by propeller and exhaust blast.

  c. Local natural materials often can be used for rapid construction of a base course for all-weather operations. To meet construction time requirements the materials must be relatively near the site and easily recovered from the deposits. To serve without a steel landing mat or a pavement, the base-course material must be a type that compacts readily into a stable mass. Examples are graded gravel containing some natural binder, coral, and sand-clay.

72. TIME REQUIRED TO CONSTRUCT ADVANCED LANDING FIELDS. Caution: The following statements of time cannot be used for estimating a particular job. Each project must be reconnoitered and estimated individually. See paragraph 69 and chapter 21. The figures given below are from records of aviation engineer units in various theaters and are presented primarily to emphasize the speed with which advanced landing fields must be built.
  a. Dry-weather advanced landing fields have been constructed by one battalion at favorable sites in flat terrain in from 1 to 3 days, including time for reconnaissance. At less favorable sites, where more clearing and grading are required, the time varies from 3 to 10 days.
  b. One battalion has constructed all-weather advanced landing fields in 10 to 21 days. On most of them steel landing mats were used on the natural subgrade; on others base courses of local natural materials were used without surface treatment, or surfaced with steel landing mat or bituminous treatment.
  c. Captured enemy airdromes have been restored for use as advanced landing fields in 1 to 3 days depending upon the amount of drainage and the number of mines and booby traps encountered.

73. AIR OPERATIONS AT ADVANCED LANDING FIELDS. Engineer troops frequently must assist air operations at advanced landing fields. To do so they must be familiar with runway marking procedure (par. 178) and signals for maneuvering planes on the ground (table XLI, app. II), control tower operations and signals (table XLII, app. II), flight patterns, and servicing of aircraft.

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