While the combat engineers continued their steady movement along Route 9, additional elements of the airmobile armada were thrown into the action. On D plus two, the 2d Brigade, 1st ACD which had been staging at Ca Lu conducted a vertical envelopment into LZ Tom and LZ Wharton which were roughly 6,000 and 8,500 meters southeast of Khe Sanh. The air assault went smoothly even though the zones were shelled by NVA gunners. By the end of the day, all 2d Brigade units were in position along with three batteries of the 1st Battalion, 77th Artillery. In the meantime, the 3d Brigade and the 1st Marines expanded their TAORs along Route 9.(206) On 4 April, General Tolson began to put the squeeze on enemy elements to the south of the KSCB. Moving northeast from LZ Wharton, the 1/5 CavSqd attacked the old French fort near the junction of Route 9. At the same time, the 26th Marines, which had been attached to the 1st ACD since 31 March, began the long awaited breakout from the base. At 0600, three companies of Lieutenant Colonel John J. H. Cahill's 1/9 (relieved Lieutenant Colonel Mitchell on 1 April) moved out of the rock quarry perimeter and advanced on Hill 471 which was 2,500 meters due south of the airstrip. The hill was a key terrain feature since it overlooked the road junction and that segment of Route 9 which snaked to the southwest. The area was also occupied by major elements of the =304th NVA Division=. After heavy prep fires, the Marines stormed up the slope in the face of light enemy fire and secured their objective at 1720.[71] Thirty North Vietnamese bodies were strewn over the hilltop. The men of 1/9, however, were in for a long night. Later that night, the enemy lashed out at the hill with 192 mortar and artillery rounds. The barrage was undoubtedly designed to soften up the Marines for a counterattack the next morning. The North Vietnamese might as well have saved their ammunition and their counterattack.(207) At 0515, the =7th Battalion=, =66th Regiment=, =304th NVA Division=, charged up Hill 471 in a vain attempt to knock 1/9 from the crest. The =66th Regiment= was definitely a hard-luck outfit; it had been bloodied at Khe Sanh Village on 21 January and again during the abortive attack against the 37th ARVN Ranger Battalion, on 29 February/1 March. The enemy's string of bad luck remained unbroken on the morning of 5 April. Lieutenant Colonel Cahill's Marines stood their ground, poured withering fire into the onrushing enemy troops, and, with the aid of artillery and tactical air strikes, smashed the North Vietnamese attack. During the one-sided exchange, one Marine was killed and 19 wounded; the =66th Regiment= left 122 dead on the slopes. This fight was one of the major highlights of Operation PEGASUS.[72](208)