soldiers". It was estimated that although they provided 50% of the manpower, the RF and PF cost only 5% of total military costs. During his period in charge of IV Corps, the region's regular forces were depleted because a proportion of them were across the border as part of the Cambodian Campaign, seeking to destroy PAVN/VC jungle bases, supplies and staging grounds for an invasion into South Vietnam. Trưởng used the RF/PF that he had enhanced to fill the void, and they strengthened the government control in the region despite having nominally less resources. In the forests surrounding U Minh, Trưởng's outpost building programs resulted in a record number of defectors as the populace became more confident in his forces' ability to provide security. When American Ambassador Ellsworth Bunker came to inspect an outlying military base that Trưởng had built, he asked if the general intended to stay there. Trưởng replied "Yes, forever". Trưởng was so successful in pacifying the Mekong Delta that he allowed some of his forces to be redeployed to other parts of South Vietnam. Known for his unbending integrity, Trưởng vigorously moved against "ghost" and "ornamental" soldiers, deserters and conscription evaders in his region. Abrams said that only Trưởng and Phạm Văn Phú among the division and corps commanders had not begun to psychologically crack under the pressure of the PAVN onslaught. During the PAVN's Easter Offensive) of 1972, he was given command of I Corps, replacing the disgraced Lieutenant General Hoàng Xuân Lãm. General Trưởng held PAVN forces at bay before Huế and then launched (against the initial resistance of President Nguyễn Văn Thiệu and MACV) Operation Lam Son 72. During the counteroffensive, he successfully pushed PAVN forces back to the city of Quang Tri (which was retaken in September) and advanced on to the Cửa Việt river. Collapse of South Vietnam Trưởng remained in command of I Corps until the collapse of South Vietnam, when the north of the country lapsed into anarchy amid confused leadership by President Thiệu. I Corps fielded three infantry divisions, the elite Airborne and Marine Divisions, four Ranger Groups and an armored brigade. Until mid-March, due to Trưởng's highly effective leadership, the PAVN had only tried to cut the highways, despite having five divisions and 27 further regiments far outnumbering Trưởng's men. At a meeting on 13 March, Trưởng and the new III Corps commander, Lieutenant General Nguyễn Văn