from 29 March 1966 to 15 September 1967. From January to April 1967 the 7th Marines conducted Operation Desoto. In early April 1967 under Operation Oregon the division moved north to Da Nang to support the 3rd Marine Division and Task Force Oregon took over the division's former TAOR. From April to May Division units conducted Operations Union and Beaver Cage. From May to June the 5th Marine Regiment conducted Operation Union II with Army of the Republic of Vietnam (ARVN) forces. In September Division units and ARVN forces conducted Operation Swift. In November the 5th Marines conducted Operation Essex. On 4 December 1967 Task Force X-Ray was activated to implement Operation Checkers, the movement of the 1st Marine Division from Thừa Thiên Province north to Quảng Trị Province to support the 3rd Marine Division which was engaged in heavy combat along the Vietnamese Demilitarized Zone. From 28 December 1967 to 3 January 1968 Division units conducted Operation Auburn on Go Noi Island south of Da Nang. On 11 January 1968 Task Force X-Ray headquarters was established at Phu Bai Combat Base and assumed operational control of the 5th Marine Regiment which moved north from Da Nang and the 1st Marine Regiment already based at Phu Bai. When the 1968 Tet Offensive began at the end of January, the division was involved in fierce fighting with PAVN/VC throughout its TAOR and together with ARVN units would defend Da Nang and fight the Battle of Huế. The 1st Marines would receive a Presidential Unit Citation for its actions at Huế. From May to August Division units conducted Operation Allen Brook on Go Noi Island. From May to October Division units conducted Operation Mameluke Thrust in Happy Valley southwest of Da Nang. From 1 to 19 October Division units conducted Operation Maui Peak to relieve Thường Ðức Camp. From late October to early December the 5th Marines conducted Operation Henderson Hill in Happy Valley. From 20 November to 9 December Division units conducted Operation Meade River south of Da Nang. From 6 December to 8 March 1969 Division units conducted Operation Taylor Common in the An Hoa Basin west of Hội An. From 31 March to 29 May 1969 Division and ARVN units conducted Operation Oklahoma Hills southwest of Da Nang. From 26 May to 7 November Division, ARVN and Republic of Korea Marine Corps (ROKMC) units conducted Operation Pipestone Canyon on