First Marine Division orders called for an elaborate series of deceptions. Immediately prior to CLAM-UP, on 9–10 February, the 11th Marines fired 471 harrassing and interdiction missions, as if to cover a large-scale withdrawal. Over 12,000 artillery rounds were expended.[353] Then CLAM-UP commenced, and the three regiments on the MLR—from left to right, the KMCs, 1st Marines, and 7th Marines—did their part to hoodwink the enemy. Reserve battalions executed daylight marches on foot to the rear and returned after dark by means of motor lifts. The 5th Marines, in Division reserve at Camp Tripoli, executed similar feigned withdrawals.
[353] 11thMar HD, Feb 52, 13; Col B. T. Hemphill comments, 20 Jan 59.
After the Marine cannoneers completed their supposed covering fires, the front was plunged into an eerie silence. It did not take long, of course, for the enemy’s curiosity to be aroused. NKPA patrols reconnoitred the Marine lines on the night of 10–11 February without being fired upon. The following night a patrol attempted to draw Marine fire in the Hill 812 area by advertising its presence with loud talk. The enemy’s fire was not returned until the patrol attacked a Marine position with white phosphorous grenades. In sheer self-defense the Marines retaliated, and the North Koreans made a hurried exit, leaving behind 10 dead and 2 wounded men who became prisoners.
At first light on the 12th another enemy patrol tried to penetrate the wire in front of a 1st Marines position and paid the penalty with nine men killed and three wounded in a 15-minute fire fight.
On 13 February the Marines were pounded with the month’s heaviest concentration of NKPA fire—344 artillery and 1,469 mortar rounds. Thus did the enemy serve notice of his realization that Marine positions on the MLR were being held in strength. NKPA patrol actions on the nights of the 13th and 14th were launched at Marine trenches on Hills 812 and 854 at the estimated cost of heavy casualties.
When Operation CLAM-UP came to an end on 15 February, it had admittedly fallen short of EUSAK expectations. Although NKPA patrol losses had been considerable, they were offset by fewer casualties in rear areas enjoying a five-day immunity from UN artillery fire. Worse yet, the enemy was enabled during this period of grace to bring up ammunition and other supplies without interference. As a final disillusionment, it was reckoned that across the whole Eighth Army front the Communists had lost fewer prisoners than during the preceding five-day period.
In the Marine combat zone a gain was recorded in enemy casualties. General Selden congratulated the Division on “the fire discipline practiced by MLR troops and by platoon and company commanders. As a consequence of the fire discipline, the line companies were able to kill 56 enemy and wound 54.” These totals, it was pointed out, were larger than the losses normally inflicted on the enemy in a five-day period.[354]
[354] 1stMarDiv HD, Feb 52, 3.
On the other hand, five deserters from the mortar company of the 1st Battalion, 91st Regiment, 45th NKPA Division revealed that advantage had been taken of Operation CLAM-UP by detailing mortar personnel and men from the rifle companies to carry ammunition. During the five-day lull, according to the prisoners, 2,600 rounds were brought up for the company’s nine mortars.[355]
[355] 1stMarDiv PIR No. 486, Feb 52.