Although a great deal of useful data was compiled, some disturbing questions remained. How high were the sea walls of Inchon? Were the mud flats suitable for landing either troops or vehicles at low tide? Approximately how many NKPA guns were hidden on Wolmi-do?... These were some of the intelligence gaps which must be filled before an effective plan could be drawn up for an assault landing.
PhibGru One made its material available to the G-2 Section of the 1st Marine Division, and the two staffs worked together on the Mount McKinley in close cooperation. Attached were the 163d Military Intelligence Service Detachment (MISD) and the 441st Counter Intelligence Corps (CIC) Team. Both of these units had been furnished by FECOM and consisted of Army commissioned and enlisted personnel as well as native Koreans serving in liaison, interpretation, and translation capacities.
Even when a question could not be answered conclusively, it was up to the G-2 sections of the Attack Force and Landing Force to arrive at a conclusion for planning purposes. For instance, it was never satisfactorily determined from available sources—JANIS publications, strategic engineering studies, Naval Attaché reports, and photographic interpretation reports—whether LVTs would be able to traverse the mud flats of the Inchon harbor area. And since there remained some doubt, planning proceeded on the assumption that the answer was negative. This proved to be the correct as well as the prudent decision, later developments revealed.
Another G-2 planning problem concerned the effect that the height of the sea walls would have upon the landing. Photographs at hourly stages of the tide made it appear that the masonry was too high for the dropping of ramps at any time. As a solution, G-2 officers hit upon a device reminiscent of the storming of castles during the Middle Ages. Scaling ladders were recommended with the suggestion that they be built of aluminum with hooks at one end to be attached to the masonry. Construction was started at Kobe, but the order could be only partially filled before D-day, and wooden ladders were built as substitutes.
It is hardly necessary to point out the importance of estimates as to the numbers and defensive capabilities of the enemy. Yet the G-2 sections on the Mount McKinley were up against a peculiar situation cited in the 1st Marine Division report:
“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.”[93]
[93] This account of G-2 planning for Inchon is based upon 1st MarDiv SAR, Annex Baker.
Photographic coverage showed the Inchon harbor area to be honeycombed 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.[94]