What did Phu Bai have to do with the Vietnam War?

Phu Bai was a small enclave in Thua Thien Province due South Quang Tri Povince on Highway One. Phu Bai was originally home to a small Army Security Agency unit known as Detachment J, 3rd RRU. Quartering party elements of this unit arrived there in January, 1963. Much later, in March, 1965, General Westmorland ordered the Marines to establish it as the second Marine Corps camp in Vietnam. A thousand Marines spent a month there digging in and filling a million sand bags before Westmorland allowed them to move out and head for areaslike Gio Linh, Con Thien, Cam Lo and Khe Sanh. It grew to be quite a large base, with excellent riverine facilities. But after the Marines left, it was under Army control. In Marine lore it was the Acapulco or Venice that the Marines built as an Army rest home. This is an exaggeration, as is often the case in Marine Lore. The Army was there long before the Marines and remained after they left. It wasn't, but it was a constant thorn in the heel of the Marines that toiled there in the sand bag capitol of Vietnam.
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Phu Bai was a village in Vietnam that was the location of a large military base.
Phu Bai was the location of Camp Hochmuth. Major General Bruno A. Hochmuth , was a Marine killed in combat just north of Hue.
In 1968 it was the location of PCV HQ, Provisional Corps Vietnam. It later became the HQ of XXIV Corps which was responsible for all of the units in the northern 2 provinces of I Corps Tactical Zone. XXIV Corps was under the command of III MAF HQed in Da Nang. It was located next to the Hue-Phu Bai airport just south of the City of Hue where the old Imperial palace is located at the Citadel.
Under XXIV Corps were the 1st Air CAV, Div. , 101 st Airborne Div., the 3rd Marine Div and the 1st ARVN Div. as well as many subordinate units, such as aviation, arty, SOG units, signal, medical and opcon infantry units. Towards the end of the war, HQ XXIV Corps was relocated to Da Nang, and eventually stood down, retiring its colors to Hawaii (I believe).
GRS Added:
I was stationed in Phu Bai for 16 months. Jul-'68 to Nov-'69 at G2 XXIV Corps. Phu Bai was hit by 122 mm rockets many times during my tenure there. In June 1969 Phu Bai was attacked with 122s which destroyed the PX complex. A 122 wiped out an entire 204 MID hooch. Luckily all the occupants were at work in HQ building. The 204th perimeter was also hit one night, but no one sustained and serious injuries, just some scratches and bruises. No penetrations that I know of.