Dean ordered one battery of 155-mm. howitzers of the 11th Field Artillery Battalion to Choch'iwŏn for direct support of the 21st Infantry.
78th tanks + 24th Recon Tanks + 3rd Engineer
Also in support of the regiment were A Company, 78th Heavy Tank Battalion, (M24 light tanks) less one platoon of four tanks, replacing the 24th Reconnaissance Company tanks, and of the B Company, 3d Engineer Combat Battalion.
"The first engagement between US and North Korean tanks occurred near Ch'ŏnui. One enemy T34 was destroyed while two outclassed US M24 Chafee light tanks were lost. Near P'yŏngt'aek, the Air Force achieved its greatest single day destruction of enemy tanks and trucks during the war."
In the afternoon, tanks participated in the 3d Battalion counterattack and did better. One of them got in a first shot on an enemy tank and disabled it. Two American light tanks were lost during the day. [07-35]
Four tanks of A Company, 78th Heavy Tank Battalion, were lost to enemy action north of Choch'iwŏn on 10 and 11 July. [07-44]
Comments: My father, Norman W. Hammes, was a platoon leader in Company A,
78th Heavy Tank Battalion. His was the first tank unit to land in South Korea in early July 1950.
When they entered combat somewhere south of Osan, covering the withdrawal, they had no armor piercing or HE ammunition for their main guns, only practice rounds, which fragmented well for anti-personnel use, but were hopeless against the North Korean T-34 tanks. They could only hope for a lucky shot to knock off a track or jam the turret ring of the T-34s. The M-24's were so lightly armored that when they returned to the lager to re-arm, they used tent pegs to plug the holes in the sides of the turrets where they'd been hit by N.K. anti-tank rifles.
Their M-24's didn't last long against the T-34's. They had all been destroyed within a couple of months and the battalion was disbanded, re-equipped, I believe with M-4's, and remade into a recon unit, according to what I've read.