On 19 May, a PAVN rocket attack on Camp Evans caused an ammunition dump to explode starting a fire that spread to the airfield damaging or destroying 124 aircraft of the 1st Brigade, 1st Cavalry Division rendering the brigade combat ineffective for a week until replacement helicopters arrived. Allied spoiling operations, in particular Operation Carentan and Operation Delaware had so disrupted the PAVN logistic network that the PAVN's Military Region Tri-Thua-Thien headquarters was unable to mount any major attack on Huế. PAVN/VC operations against Da Nang were forestalled by the 1st Marine Division's Operation Allen Brook from 4 May to 22 August on Go Noi Island 25 km south of Da Nang which resulted in 917 PAVN/VC killed and 11 captured for the loss of 172 Marines killed and Operation Mameluke Thrust from 19 May to 23 October in Happy Valley southwest of Da Nang which resulted in 2,728 PAVN killed and 47 captured for the loss of 269 Marines. The PAVN's main objective in southern I Corps was to destroy the Khâm Đức Special Forces camp in western Quảng Tín Province to create an infiltration route from Laos to the Quế Sơn Valley. While the U.S. initially planned to build up forces for a major battle at Khâm Đức, they then decided to withdraw rather than tie down their forces in what could become a prolonged siege as had just ended at Khe Sanh. In a battle that lasted from 10 to 12 May the PAVN overran the outposts surrounding Khâm Đức and harried the withdrawing U.S. and ARVN forces. In the Battle of Landing Zone Center from 5–25 May the PAVN 31st Regiment lost 365 killed. In the Battle of An Bao from 5–6 May elements of the PAVN 3rd Division ambushed a unit of the 1st Battalion, 50th Infantry Regiment (Mechanized) losing 117 killed for the loss of 18 U.S. killed. On 10 May the PAVN 2nd Regiment was seen near the hamlet of Trung Hoi (2), west of Landing Zone Uplift. On the morning of 11 May Companies B and C, 1/50th Infantry and 2 M42 Dusters moved along Route 506 4 km west of LZ Uplift to investigate the sighting finding an abandoned battalion-size trench complex off Route 506.