On 30 August, ComNavFE issued his Operation Plan 108–50, assigning to JTF–7, of which X Corps was a part, the mission of seizing by amphibious assault a beachhead at Inchon. X Corps OpnO No. 1 was dated on the 28th, though not received by Division until the 30th.
By that time, Division planning had made so much progress that Embarkation Order 1–50 was issued on the last day of the month, followed on 4 September by the final draft of Division OpnO 2-50.
Operations orders of JTF–7 and TF–90 were issued concurrently.
“Our accumulated knowledge of the enemy’s military tactics, prior to our landing at Inchon on 15 September 1950, consisted almost in its entirety of knowledge about the enemy’s offense. . . . With but few exceptions, UN forces were forced to take a defensive stand and denied the opportunity to study large scale enemy defensive tactics from actual combat. Thus it was that our assault landing was made with relatively little prior knowledge regarding the enemy’s probable reaction to a large-scale offensive of this nature, particularly when it involved the penetration into the very heart of his newly acquired domain”
Photographic coverage showed the Inchon harbor area to be honey-combed with gun positions and other defensive installations. On the other hand, daily aerial observation indicated that most of them were not occupied. G–2 conclusions during the planning phase often had to be based on such conflicting evidence, even though the penalties of faulty interpretation might be drastic. But after being viewed with due suspicion, signs of negative enemy activity were finally accepted as valid in estimates of light to moderate NKPA resistance. “Sadly lacking as was information on the objective area,” commented the Division G–2 report, “more so was that on the enemy in the area.” Early in September, however, the Attack Force and Landing Force concurred in the initial X Corps estimate of 1,500 to 2,500 NKPA troops in the immediate area, consisting largely of newly raised personnel.
Radio reports of first-hand observations in the objective area, though coming too late for initial planning purposes, confirmed some of the G–2 estimates. This dangerous mission was undertaken by Lieutenant Eugene F. Clark, a naval officer on General MacArthur’s JSPOG staff. U.S. and British Marines provided an escort on 1 September when the British destroyer HMS Charity (R-29) brought him from Sasebo to a point along the coast where the South Korean patrol vessel PC 703 waited to land him at Yŏnghŭng-do, an island about 15 miles southwest of Inch'ŏn.
Clark went ashore with a small arsenal of firearms, grenades and ammunition, as well as 30 cases of C rations and 200 pounds of rice. He quickly made allies of the 400 friendly Korean inhabitants of the island and organized his own private little “army” of about 150 youths from 14 to 18 years old. These “troops” were posted about Yŏnghŭng-do for security, since the near-by island, Taebu-do, was occupied by 400 NKPA soldiers within wading distance at low tide.
The naval officer had no illusions as to what his fate might be in the event of capture. Day and night, he kept a grenade within reach, since he did not intend to be taken alive. When the long expected enemy attack from Taebu-do materialized, he commandeered a “one-lung” South Korean motor sampan and fought it out with the NKPA motor sampan escorting boats filled with soldiers. The enemy began the strange “naval” battle with a few badly aimed rounds from a 37mm tank gun. Clark and his crew of three friendly Koreans finished it with a long burst from a .50 caliber machine gun. After sinking the NKPA motor sampan, he destroyed another boat with 18 soldiers aboard and captured three prisoners for questioning.
One night the intrepid lieutenant rowed a dinghy to the Inch'ŏn sea wall. When the tide went out, he tested the mire by wading in it up to his waist. This experience led to the sending of a radio report, “Inch'ŏn not suitable for landing either troops or vehicles across the mud.”
Korean youths, posing as fishermen, brought intelligence which Clark included in his daily radio messages. One of these spies made an effort to count the guns on Wŏlmi-do and describe the locations. Others took measurements of the Inch'ŏn sea wall and penetrated as far inland as Seoul to report numbers and positions of NKPA troops.
Clark declined all offers to evacuate him. As the climax of his exploit, he managed to restore the usefulness of the lighthouse on P'almi-do Island which the enemy had put out of commission. This structure, the former entrance beacon for Inch'ŏn by way of Flying Fish channel, served him as a refuge when he had to leave Yŏnghŭng-do hurriedly just ahead of NKPA troops who landed in force and butchered 50 civilians of both sexes. Clark, who received a Silver Star, stuck it out on P'almi until midnight of 14 September, when he turned on the beacon light to guide the amphibious task force.
The Inch'ŏn-Seoul Operation, Ch 4, Intelligence Planning for Inch'ŏn Page 2 of 2
The Inch'ŏn-Seoul Operation
Lynn Montross and Nicholas A. Canzona
Chapter 4. The Planning Phase
The Landing Force Plan
The decisions behind the Landing Force Plan—1st Marine Division OpnO 2–50—obviously had to be made without benefit of Lieutenant Clark’s reports, since the publication date was 4 September 1950. It is to the credit of these conclusions, therefore, that so few of them had to be corrected in the light of first-hand evidence from the objective area.
Although CG X Corps was the assigned Expeditionary Troops Commander, planning on the Corps level was concerned almost entirely with the exploitation phase following the seizure of the beachhead. All Landing Force planning was done on the Mount McKinley by the Division in close coordination with PhibGru One. The first consideration, as viewed by the Navy planners, was that the tides, currents, and tortuous channels of Inch'ŏn made necessary a four-hour daylight approach to the transport area. This meant that 1130, at low tide, was the earliest hour of arrival; and not until about 1700 would the next high tide provide enough water for an assault landing.
On 15 September a maximum high tide of 31 feet could be expected at 1919. Evening twilight came at 1909 [I have 1905] . It was estimated initially that 23 feet of water would take the LCVPs and LVTs over the mud flats, but that 29 feet were necessary for the beaching of the LSTs.
In view of these conditions, PhibGru One planners concluded that 1700 was the best time for landing the LCVPs and LVTs, and it was decided to beach the LSTs at about 1900. Simultaneous landings of troops on Wŏlmi-do and the mainland were contemplated.
This was the point of departure for Division planners. They maintained that Wŏlmi-do was the key terrain feature, and that it should be secured first in a separate landing. The logical course, according to the Marines, would be to utilize the morning high tide for the seizure of this island commanding the waterfront. The enemy would be given the whole day in which to prepare for the attack on the mainland; but the Landing Force could also utilize this period for cleaning up Wŏlmi-do and moving in supporting artillery.
It was typical of the harmony prevailing between the two planning groups on the Mount McKinley that PhibGru One immediately accepted the concept of a double-barreled attack. The rub was that a night approach would be necessary to assault Wŏlmi-do at 0600 on the morning high tide, and the Navy doubted the feasibility of a movement of the slow-moving and un-maneuverable APAs, AKAs, and LSTs through winding, mud-lined channels in the darkness.
At length a compromise was reached with the decision to employ DD, APD, and LSD types primarily, which were more maneuverable in addition to being equipped with radar navigational instruments. The morning landing on Wŏlmi-do was to be made with a single battalion of the 5th Marines, to be designated by the Brigade. On the mainland the remaining two battalions would land with the evening high tide on RED Beach, just north of the causeway connecting the island with the city, while two battalions of the 11th Marines landed in support on Wŏlmi-do. Meanwhile the 1st Marines was to hit BLUE Beach, southeast of the urban area. And after driving rapidly inland to consolidate their positions before nightfall, the two Marine regiments were to make a junction in the morning and seize the beachhead while the 17th ROK Regiment (later replaced by 1st KMC Regiment) mopped up the city streets.
Marine G–4 planners suggested one of the most daring of all the calculated risks. This was the decision to use LCVPs for the RED Beach landings because their comparative speed would clear the landing area for the beaching of eight LSTs—all that could be crammed into the narrow confines of this strip of urban waterfront.
The Inch'ŏn-Seoul Operation, Ch 4, The Landing Force Plan Page 1 of 2
Each was to be loaded with ammunition, rations, water, and fuel. Obviously these Navy workhorses, nicknamed “large slow targets”, would be easy marks for NKPA shore guns, but this was a chance that had to be taken if the assault troops were to be adequately supplied.
There was not time, of course, to unload and retract the ships during the period of evening high tide. They must be unloaded during the night and taken out on the morning tide.
Since it was not considered feasible to land LSTs on BLUE Beach, that area would not be developed beyond the needs of the immediate assault. For this purpose, 16 preloaded LVTs were to be used as floating dumps until the 1st Marines could link up with the other regiment.
These were the essentials of the Landing Force plan. H-hour was ultimately determined from a study of late photographs which brought about a slight change in estimates. Since a tide of 25 feet (two feet higher than the initial estimate) appeared to be necessary for the LCVPs and LVTs to reach the sea wall, H-hour was set at 1730 instead of 1700. The completed Landing Force plan provided for these steps:
(1) BLT–3 of RCT–5 to land on Beach GREEN at L-hour on D-day and seize Wŏlmi-do. (2) RCT–5 (- BLT–3) to land on Beach RED at H-hour, seize Objective O-A, effect a juncture with RCT–1, and prepare for further operations to the east in coordination with RCT–1 to seize the FBHL. (3) RCT–1, to land on Beach BLUE, with two battalions in assault, seize Objective O–1, and prepare for further operations to the east in coordination with RCT–5 to seize the FBHL. (4) 11th Marines (– 3d Bn) (96th F. A. Bn, USA, attached) to land 1st and 2d Bns on Beach GREEN at H-hour, occupy positions on Wŏlmi-do and support seizure of the beachhead with priority of fires to RCT–1. Remainder of artillery to land on call. (5) ROK Marines, initially in Division reserve, to land over Beach RED on call and conduct operations to occupy the city of Inch'ŏn in coordination with RCT–5. (6) 1st Tank Bn (–) (Reinf.) to be prepared to land on order one company in LSU on Beach GREEN, remainder of battalion on order on beaches to be designated. (7) 1st Engr Bn (–) to land on Beach RED or in harbor on order, assume control of detached companies on order, and support seizure of beachhead as directed. Priority to opening and maintaining MSR along southern edge of the city to RCT–1 zone of action. (8) 1st Shore Party Bn (–) to land on order on Beach RED or in harbor and assume control of shore party activities on Beaches RED and GREEN. (9) 1st Amph Trac Bn to transport and land elements of RCT–1 on Beach BLUE and continue support of RCT–1 until released. (10) 2d Engr Spl Brig, USA (Reinf.) to furnish ships platoons and augment Division shore party as requested. After landing and when directed, to assume operational control of Division shore party and responsibility for control of all port operations. To provide logistical support of 1st MarDiv.
The Inch'ŏn-Seoul Operation, Ch 4, The Landing Force Plan Page 2 of 2
The Inch'ŏn-Seoul Operation
Lynn Montross and Nicholas A. Canzona
Chapter 4. The Planning Phase
Availability of Brigade Troops
The old recipe for rabbit stew began, “First, catch your rabbit.” And while the Landing Force plan was being formulated, General Smith had no assurance for a few days that he could count on having the whole of his landing force available.