Upon its arrival in West Korea, the 1st Marine Division was under orders to relieve the 1st ROK Division and take over a sector at the extreme left of the Eighth Army line, under I Corps control, where the weaknesses of Kimpo Peninsula defenses had been of considerable concern to EUSAK and its commander, General James A. Van Fleet. As division units reached their new sector, they moved to locations pre-selected in accordance with their assigned mission. First Marine unit into the I Corps main defensive position, the JAMESTOWN Line, was the 1st KMC Regiment attached to the division, with its organic artillery battalion. The KMCs, as well as 1/11, began to move into their new positions on 18 March. At 1400 on 20 March, the Korean Marines completed the relief of the 15th Republic of Korea Regiment in the left sector of the MLR (main line of resistance). Next into the division line, occupying the right regimental sector adjacent to the 1st Commonwealth Division, was Colonel Sidney S. Wade’s 1st Marines with three battalions forward and 2/5 attached as the regimental reserve. Relief of the 1st ROK Division was completed on the night of 24–25 March. At 0400 on 25 March the Commanding General, 1st Marine Division assumed responsibility for the defense of 32 miles of the JAMESTOWN Line. That same date the remainder of the Marine artillery battalions also relocated in their new positions.
As the division took over its new I Corps mission on 25 March, the Marine commander had one regiment of the 1st ROK Division attached as division reserve while his 5th Marines was still in the east. Operational plans originally had called for the 5th Marines, less a battalion, to locate in the Kimpo Peninsula area where it was anticipated Marine reserve units would be able to conduct extensive amphibious training. So overextended was the assigned battlefront position that General Selden realized this regiment would also be needed to man the line. He quickly alerted the 5th Marines commanding officer, Colonel Thomas A. Culhane, Jr., to deploy his regiment, then en route to western Korea, to take over a section of the JAMESTOWN front line instead of assuming reserve positions at Kimpo as originally assigned. General Selden believed that putting another regiment on the main line was essential to carrying out the division’s mission, to aggressively defend JAMESTOWN Line, not merely to delay a Communist advance.
Only a few hours after the 5th Marines had begun its trans-Korea move, helicopters picked up Colonel Culhane, his battalion commanders, and key regimental staff officers and flew them to the relocated division command post (CP) in the west. Here, on 26 March, the regimental commander officially received the change in the 5th Marines mission. Following this briefing, 5th Marines officers reconnoitered the newly assigned area[15] while awaiting the arrival of their units. When the regiment arrived on the 28th, plans had been completed for it to relieve a part of the thinly-held 1st Marines line. On 29 March, the 5th Marines took over the center regimental sector while the 1st Marines, on the right regimental flank, compressed its ranks for a more solid defense.
[15] Col Thomas A. Culhane, Jr. ltr to Hd, HistBr, G-3 Div, HQMC, dtd 16 Sep 59, hereafter Culhane ltr.
Frontline units, from the west, were the 1st KMCs, the 5th, and 1st Marines. To the rear, the 7th Marines, designated as division reserve, together with organic and attached units of the division, had established an extensive support and supply area. As a temporary measure, a battalion of the division reserve, 2/7, was detached for defense of the Kimpo Peninsula pending a reorganization of forces in this area. Major logistical facilities were the division airhead, located at K-16 airfield, just southwest of Seoul, and the railhead at Munsan-ni, 25 miles northwest of the capital city and about five miles to the rear of the division sector at its nearest point. Forward of the 1st Marine Division line, outposts were established to enhance the division’s security. In the rear area the support facilities, secondary defense lines, and unit command posts kept pace with development of defensive installations on the MLR. Throughout the 1st Marine Division sector outpost security, field fortifications, and the ground defense net were thorough and intended to deny the enemy access to Seoul.
The Marines’ Home in Western Korea[16]
[16] Unless otherwise noted, the material in this section is derived from: 1stMarDiv ComdD, Mar 52; CIA, NIS 41B, South Korea, Chap I, Brief, Section 21, Military Geographic Regions, Section 24, Topography (Washington: 1957–1962); Map, Korea, 1:50,000, AMS Series L 751, Sheets 6526 I and IV, 6527 I, II, III, and IV, 6528 II and III, 6627 III and IV, and 6628 III (prepared by the Engineer, HQ, AFFE, and AFFE/8A, 1952–1954).
In western Korea, the home of the 1st Marine Division lay in a particularly significant area. (See [Map 2].) Within the Marine boundaries ran the route that invaders through the ages had used in their drive south to Seoul. It was the 1st Marine Division’s mission to block any such future attempts. One of the reasons for moving the Marines to the west[17] was that the terrain there had to be held at all costs; land in the east, mountainous and less valuable, could better be sacrificed if a partial withdrawal in Korea became necessary. At the end of March 1952, the division main line of resistance stretched across difficult terrain for more than 30 miles, from Kimpo to the British Commonwealth sector on the east, a frontage far in excess of the textbook concept.
[17] The two other reasons were the weakness of the Kimpo defenses and abandonment of plans for an amphibious strike along the east coast. Montross, Kuokka, and Hicks, USMC Ops Korea, v. IV, p. 253. Planning for a Marine-led assault had been directed by the EUSAK commander, General Van Fleet, early in 1952. The Marine division CG, General Selden, had given the task to his intelligence and operations deputies, Colonel James H. Tinsley and Lieutenant Colonel Gordon D. Gayle. On 12 March General Van Fleet came to the Marine Division CP for a briefing on the proposed amphibious assault. At the conclusion of the meeting the EUSAK commander revealed his concern for a possible enemy attack down the Korean west coast and told the Marine commander to prepare, in utmost secrecy, to move his division to the west coast. Lynn Montross, draft MS.
Although Seoul was not actually within the area of Marine Corps responsibility, the capital city was only 33 air miles south of the right limiting point of the division MLR and 26 miles southeast of the left. The port of Inchon lay but 19 air miles south of the western end of the division sector. Kaesong, the original site of the truce negotiations, was 13 miles northwest of the nearest part of the 1st Marine Division frontline while Panmunjom was less than 5 miles away and within the area of Marine forward outpost security. From the far northeastern end of the JAMESTOWN Line, which roughly paralleled the Imjin River, distances were correspondingly lengthened: Inchon, thus being 39 miles southwest and Kaesong, about 17 miles west.