Organization of New Defense Positions[675]
[675] Unless otherwise noted, the material in this section is derived from: 1stMarDiv ComdDs Jul-Sep 53; 1stMarDiv Type “C” Rpt Defense of “C” Sector, 27 Jul-31 Oct 53, Folder #3 (this and following 1stMarDiv end-of-war records retired in 61 A2265, Box 74, FRC, Suitland, Md.); 1stMar Hist of Defense of “D” Sector, 27 Jul-31 Oct 53, Folder #3 (contains brief histories of individual units); 5thMar Hist of Defense of “D” Sector, 27 Jul-31 Oct 53, in Folders #3 and #4; 7thMar Hist of Defense of “D” Sector, 27 Jul 53–10 Feb 54, in Folder #5; 1stMarDiv Type “C” Rpt Defense of “C” Div Sect, 27 July-31 Dec 53, Folder #6 (containing, among others, brief rpts 11thMar, 1st TkBn, 1st EngrBn, 1stMTBn, 7th MTBn, 1st KMC Rgt, 2d KMC Rgt).
Upon withdrawal from the demilitarized zone and organization of the MBP, the Eighth Army established its plan for defense on a wide front. This was based on the organization of strongpoints disposed in depth, with planned counterattacks by mobile reserves.
As it had during active hostilities, the 1st Marine Division in the post-armistice period continued as one of the four UNC divisions manning the general outpost and MBP in the U.S. I Corps sector. Immediately east of the division was its long-time neighbor, the 1st Commonwealth Division. Still further east in I Corps were the 1st ROK and U.S. 7th Infantry Divisions.
Since 1 August, the Marine division had continued to outpost the most favorable terrain in its sector below the southern boundary of the DMZ. The division manned the No-Pass Line and prepared its defenses to resume full scale military operations, if necessary. The Munsan-ni Provisional Command, composed of the Marine-Navy-Army personnel responsible for implementing the final prisoner exchange, was also headquartered in the 1st Marine Division sector.
The strongpoint organization of the division’s main battle position was accomplished by the deployment of the 5th Marines at the general outpost line of resistance (or OPLR, a term and concept not in use since April 1952). The outpost defense concept embodied a number of forward positions, lightly held in actual numbers of men but strongly defended in numbers of automatic weapons and firepower. (This capability was possible due to the excess number of automatic weapons on hand, above normal T/E allowances, which previously had been required by MLR defenses.) In the organization of the positions, emphasis was placed on construction of bunkered observation posts, the emplacement of automatic weapons with flanking fires, and clearing of fields of fire for these weapons.
Basically, the general concept of OPLR defense was to establish mutually supporting defensive positions across the front, as well as to develop additional defense in depth positions whose strength increased from front to rear. The positions thus formed successive defense lines, from the southern DMZ boundary—the new Marine division front—south to the KANSAS Line, the Main Battle Position. (These defense lines were the old secondary defensive lines of WYOMING, KANSAS, and KANSAS SWITCH.) The KMC, 1st Marines, 7th Marines, and other units located in the KANSAS vicinity engaged in bunker construction and trench improvement. Battalion fire plans coordinated the organic, attached, and supporting weapons. Construction of the new positions and development of the KANSAS Line would be a continuing process throughout the rest of the year.
The 1st Marines received the assignment of developing the blocking positions, most of these battalion-sized strongpoints. As in the past, division support units continued to be located in the old rear supply areas south of the Imjin. In early August the division had stationed the 7th Marines in the right sector; the 1st KMC in the center; and the 1st Marines, to the south of the KMC sector. The 11th Marines, to the rear of the 7th Marines, had displaced its artillery, relaid, and was prepared to fire in support of the general outpost and MBP. ([Map 35].) Additional artillery battalions included I Corps and army units. Essentially these were the positions held until early October when, during a period of political unrest resulting from the prisoner exchange, the 1st Marines relieved the 1st KMC/RCT in the center sector (which held the southern approaches to Freedom Bridge and the nonrepatriate war compound). The Korean unit then relocated to blocking positions and assumed the mission of reserve regiment.
MAP 35 K. WHITE