Control Measures
Line of departure (LD) should be:
(a) Clearly defined on the ground and on the map.
(b) Approximately perpendicular to the direction of the attack.
(c) Under control of friendly units.
(d) Marked on both ends.
Line of contact (LC):
If the LC is used as an LD, it is marked LD/LC.
If the LC is not used, the LD is shown by a solid line marked LD.
Phase lines (PLs) are used to control fires and unit movement and even to limit the advance of attacking elements. Units report their arrival at or clearance of a phase line, but they do not halt unless ordered to do so. A PL is drawn as a solid line with the letters PL at each end of the line or where appropriate to allow easy identification. A PL is identified further by a number, a letter, or code name, which can be phonetic letters, colors, flowers, cars, or any other code system, under or beside the PL abbreviation.
The initial delay positions (IDPs) and successive delay positions are shown on boundaries by coordination points with a solid line between them. Although most IDPs are given a code name, they may have a number, letter, or a variety of code names. The letter abbreviation (IDP) will be displayed at the flank of the coordination symbol in parentheses, or on the line itself. Its time phase is indicated as a date-time group displaying a two-digit day and a four-digit hour that are both connected. The month indicator can be three-letters typed or spelled out, depending upon the desires of the commander. The letters IDP should be placed in parentheses between the line code name, letter, or number and the date-time group.
Delay lines (DLs) indicate where a succeeding delay position is located. Delay positions (other than initial) are drawn the same as the delay lines, except that the letter abbreviation is along the line, and no abbreviation is placed to the flanks at the coordinating points.
Coordinating points are designated on boundaries as specific points for coordination of fires and maneuver between adjacent units. They are indicated whenever a boundary crosses the forward edge of the battle area and should be indicated whenever the boundary crosses the covering force. Coordinating points are also used where delay lines and internal boundaries intersect. The symbol for a coordinating point is shown by a circle with an "X" centered in it. The symbol is labeled as appropriate.
A checkpoint is shown as a number, letter, or code word inside an upright rectangle with a pointed bottom. They are easily recognizable terrain features or objects, such as crossroads, churches, lone buildings, stream junctions, hills, bridges, and railroad crossings.
Contact points, shown graphically by squares with a staff extending from the bottom center, are designated at the units to make physical contact.
A passage point, shown similar to a checkpoint with the letters PP and the number or letter designation of the passage point within the symbol, is designated along the LD or the forward edge of the battle area of the unit being passed through.
The linkup is an operation in itself and conducted as part of an airborne or airmobile operation, an attack to assist in the breakout of an airborne or airmobile operation, an attack to assist in the breakout of an encircled force, or an attack to join an infiltrating force. The battalion may participate in a linkup as part of a larger force, or it may, itself, conduct a linkup.
Points of departure symbols are similar to a checkpoint containing the abbreviation PD and a letter or number within the symbol. The point of the arrow is at the bottom of its location.
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