These hill masses so completely dominated the major enemy approaches through the division sector to the Imjin, the lower river crossing sites and bridges, that their occupation by Marine personnel was considered essential in the event of any attack. Hill 229, adjacent to the Chan-dang corridor and part of the 229-181 axis, was considered the most critical terrain feature in the entire northern section.

Key areas to the rear of the 5th Marines’ sector were the two operating bridges (Freedom in 2/5 territory and Libby on the 3/5 right) and the two interior crossing sites (Honker and Spoonbill). All provided access to the Imjin and division support units deployed on the south side of the river. In the event of threatened hostile attack, the Northern Regiment was under orders to destroy the bridges to prevent their use by the enemy on any attempted advance to the rear.

Strong perimeter defenses, called “Bridgehead Positions” were to be built by 5th Marines’ battalions. Two were to protect the two bridges and a third, to include both ferry sites. Between the forward defended localities and the rear bridgehead positions, alternate and secondary sites were organized to create mutually supporting defenses in depth. The bridgeheads were a combination of linear and strongpoint defense, capable of withstanding severe pressure.

Organization of the defensive positions in the 5th Marine sector was complicated both by peculiarities of the terrain and political restrictions due to proximity of the DMZ. In addition to the regiment’s excess frontage, the demilitarized zone immediately to the front precluded use of either aerial or motorized reconnaissance for early warning. Security measures for the OPLR were less than ideal. Neither proper patrols nor a covering force in front of the OPLR was possible; the best that could be done was to maintain patrols along the friendly side of the No-Pass Line.

As the regimental left battalion pointed out: “Location of the DMZ and the No-Pass Line made the trace of the OPLR follow an artificial and arbitrary line rather than that of the best terrain.”[676] The most critical terrain feature in the sector, Hill 155, was located just outside the southern boundary of the DMZ. Although its possession was essential to successful defense of the OPLR and the bridgehead defense positions being developed to the interior and rear of the battalion sector, Hill 155 could not be occupied because of the armistice agreement. The solution to the problem was simply to occupy the best ground adjacent to the No-Pass Line.

[676] 2/5 Hist, in 5thMar Hist, dtd 12 Dec 53, p. 4, Folder #4.

Placement of automatic weapons was a factor of great importance in organizing the defensive positions. In order to accomplish the mission of an OPLR, weapons had to be situated to bring the enemy under fire at maximum ranges. Accordingly, machine guns and other weapons were placed on high ground well to the front. Some Marines commented that:

Many individuals having the MLR concept in mind insisted that weapons should be located forward on low ground to provide grazing fire. A period of education was required. For the same reason, it was necessary to place 81mm mortar and 4.2-inch mortar positions further forward than they would normally be in support of the MLR.[677]

[677] Ibid.

The problem of establishing depth to the defensive positions was never solved to the satisfaction of everyone. This was due primarily to the extended front which necessitated using more units for support elements than would normally be done. This situation was partly alleviated by establishing some unit defensive sectors further to the rear in the company areas.