Mortars (4.2-inch) of the 1st Marines contributed heavily to the defense of the outposts. Operations reached a peak on 12–13 August when, in a 24-hour period, Captain Carl H. Benson’s mortar company fired 5,952 rounds—4,084 high explosive and 1,868 illuminating. In addition to their defensive fires, these hard-hitting weapons attacked Chinese mortars, automatic weapons, defensive positions, and troop formations with deadly accuracy.
No less precise and lethal were the fires of Captain Gene M. McCain’s gun tanks (Company C, 1st Tank Battalion), and the battalion flame tanks. Three of the latter had fired their 105s in support of the KMC on the morning of the 9th before the vehicles received orders to move east to join Company C temporarily. On the next day, 90s fired on enemy bunkers, observation posts, and trenches in the vicinity of Siberia and Stromboli. During 11 August, two gun tanks blasted at targets immediately beyond Siberia and others to the west of that outpost.
Towards the end of the 11th, the critical part of Bunker battle began for the tankers also. Those elements of Lieutenant Colonel John I. Williamson’s battalion supporting the diversion and the subsequent main attack pulled into positions south of Hill 122 on the MLR and to the right in the Company F sector. It was not until the next day that the tanks operating with the 1st Marines reached a peak in gun support for the Bunker fight. Beginning with the defense of Hill 122 from 1600 that day, and for the next 26 hours, the tankers placed 817 shells on targets effecting the Chinese capability of capturing Bunker and Stromboli. In addition to the heavy ammunition, the Company C tanks, augmented by the 1st Marines antitank platoon and five tanks from the division tank reserve, fired 32,000 rounds of .30 caliber machine gun ammunition.
Except on the 11th, most of the tank firing in the fight for Bunker Hill through 14 August was accomplished during the hours of darkness. On the latter date, the cannons and machine guns of the mediums blasted directly at Chinese outposts opposite Colonel Layer’s regiment. The number of rounds that day fell off considerably from the high on the 13th; on the 15th the tanks in the 1st Marines area did not fire at all. Heavy rain that had accompanied the late afternoon thundershower that day made movement forward to firing positions impractical. By the next day, however, the ground was solid enough to permit some maneuvering by the tracked vehicles. They fired 52 rounds of 90mm shells and 14,750 machine gun rounds at automatic weapons positions and bunkers on the western slope of Hill 122. This marked the final tank mission in support of the 1st Marines in the battle for Bunker Hill.
During the early part of the August fighting, tanks of the division were able to get the first real test of a technique of night support,[195] and at the same time experiment with a towing device to permit retrieval of disabled vehicles under fire without getting outside the tank. The use of the lights to support both the diversionary force and the defense of Hill 122 showed the value of these instruments. Lieutenant Colonel Williamson recommended that tanks be employed in pairs, one to spot and adjust fire and the other to fire. With respect to the towing device, he considered the new piece of equipment an improvement over the manual hook-up method, but noted that the device limited tank maneuverability and had a tendency when bouncing up and down over rough terrain to dig into the ground, impeding the forward progress of the vehicle.
[195] The use of fighting lights to illuminate targets for tank gunners had been undertaken in July, but the results were inconclusive, owing to failure of one of the bulbs of the two lights tested. 1st TkBn ComdD, Aug 52, App. VI, Encl. 2. Declared the G-3, 1stMarDiv: “The diversion on Siberia was 100 percent effective, due largely to the new tank battle lights which we were using for the first time.” Honsowetz ltr II.
In Retrospect[196]
[196] Unless otherwise noted, the material in this section is derived from: FMFPac, 1stMarDiv Sum, Jul-Oct 52; PacFlt EvalRpt No. 5, Chaps. 8, 9; 1stMarDiv, 1stMar ComdDs, Aug 52.
Whether the sacrifice of Siberia in favor of the seizure of Bunker justified the outcome can be determined, in part, by looking back to the division commander’s reasons for this decision. He had cited three advantages in seizing and occupying Hill 122 instead of 58A. One, tactical surprise achieved by an attack on the former, was an unqualified success. That Bunker Hill would provide more defensible terrain and at the same time add strength to the main line were two sound judgments that the test of time would bear out. The third point, that observation into the enemy’s outpost line would be increased from the higher hill, also proved to be correct.
Only the inability to neutralize Hill 58A effectively from Bunker cast any doubt on the considerations. At night the enemy could occupy Siberia both for firing positions and flank security to attack friendly forces moving down the corridor east of Hill 122. Action to counter these two enemy actions came mainly from MLR forces.