Youngdale's presence on the Westmoreland's staff ensured a Marine voice in U.S. military planning at the Saigon level. He served in that capacity until the end of July 1965 and was promoted to the rank of major general at the same time. Youngdale was also decorated with Navy Distinguished Service Medal for his staff work. Upon his return to the United States, Youngdale was appointed deputy chief of staff for administration at Headquarters Marine Corps. He then served as inspector general of the Marine Corps from August 1966 until May 1968 and received his fourth Legion of Merit for his service during this period. His second tour of duty in Vietnam began at the end of June 1968, when he was ordered to Da Nang to succeed Major General Donn J. Robertson as commanding general of 1st Marine Division. One of his first orders was to review defense plans for Da Nang TAOR and then finished the ongoing search and destroy operations Mameluke Thrust and Allen Brook. In mid-August 1968, Viet Cong (VC) began attacking forward Combined Action Platoons and Youngdale quickly recognized this as the 3rd phase of the Tet Offensive and ordered the reinforcing of the sectors which appeared to be most in danger. He subsequently launched the Operation Sussex Bay, which blocked the withdrawal of VC forces from Da Nang area. During the end of September 1968, People's Army of Vietnam (PAVN) 2nd Infantry Division launched attack on the Thường Ðức Camp, southwest of Da Nang and overran two camps outposts. Youngdale subsequently launched Operation Maui Peak in order to relieve the siege around Thường Ðức and declared the area secured on October 19. In November 1968, Youngdale also coordinated the Operation Meade River – search and destroy mission, before he was appointed Deputy Commander of III Marine Amphibious Force (III MAF) under Lieutenant General Robert E. Cushman. Because of the lack of helicopters for Marine operations, new III MAF commander, Lieutenant General Herman Nickerson Jr. ordered Youngdale to establish a special board, which was tasked with the examination of use and command and control of Marine Corps helicopter assets. Youngdale was relieved by Major General George S. Bowman Jr. in July 1969 and ordered back to the States. For his service with 1st Marine Division and III MAF, he was decorated with his second Navy Distinguished Service Medal. He also received several decorations by the Government of South Vietnam.