One of the central frustrations of the US military during the conflict was the
Democratic Republic of Vietnam's (North Vietnam) use of
Laos and
Cambodia as logistical conduits and base areas. During the administration of President
Lyndon B. Johnson, the US military was generally not allowed by its civilian commanders to widen the war by attacking the supply routes and sanctuaries in both countries due to their ostensible
neutrality. An attempt was made to capture or destroy the headquarters during
Operation Junction City, a massive search and destroy operation launched in the border region in February and March 1967. Hampering bombing runs against rebel bases like COSVN was the assistance provided by
Soviet ships in the Pacific. Soviet ships in the South China Sea gave vital early warnings to
NLF forces in South Vietnam. The Soviet intelligence ships detected American
B-52 bombers flying from
Okinawa and
Guam, and relayed their airspeed and direction to COSVN headquarters. COSVN used this data to determine probable targets, and directed assets along the flight path to move "perpendicularly to the attack trajectory". While the bombing runs still caused extensive damage, the early warnings from 1968 to 1970 prevented them from killing a single military or civilian leader in the headquarters complexes. On January 4, 1968, some of COSVN officials from Tây Ninh province encountered American soldiers when they were attempting to transfer food in the jungle,
Huỳnh Tấn Phát's daughter Huỳnh Lan Khanh was captured and started to be escorted to Saigon. During the conflict several American military aircraft were shot down. Later Khanh's body was found by Viet Cong soldiers. She was buried with two other Viet Cong soldiers who died in this conflict. Later, President
Richard Nixon authorized border reconnaissance attacks, first in 1969 in the form of the covert bombing campaign known as
Operation Menu, wherein the suspected site of COSVN in Cambodia was repeatedly and heavily bombed. In the spring of 1970, an overt ground incursion took place—-first an ARVN attack and then a joint ARVN–American attack that would later be called the
Cambodian Campaign. On March 18, the Cambodian National Assembly
officially deposed the Cambodian leader
Norodom Sihanouk and named
Lon Nol as provisional head of state. The North Vietnamese response to the coup was swift. Even before Lon Nol's March 12 ultimatum for PAVN and NFL forces to leave Cambodia, they had begun expanding their logistical system (the
Ho Chi Minh trail) from southeastern
Laos into northeastern Cambodia. After Sihanouk's overthrow and Lon Nol's anti-Vietnamese movements, PAVN launched an offensive (Campaign
X) against the Cambodian army. They quickly seized large portions of the eastern and northeastern parts of the country, isolating and besieging or overrunning a number of Cambodian cities, including
Kampong Cham. Fearing a joint ARVN–Cambodian attack after the coup, COSVN was evacuated to the newly Vietnamese-controlled
Kratié Province of Cambodia on March 19, 1970. As the PRG and NLF headquarters prepared to follow the COSVN into Cambodia on March 30, they were surrounded in their bunkers by South Vietnamese forces flown in by helicopter. Surrounded, they awaited till nightfall and then with security provided by the 7th they broke out of the encirclement and fled north to unite with the COSVN in the Cambodian Kratié province. Years later, Trương would recall that during the
escape of the Provisional Revolutionary Government just how "close [South Vietnamese] were to annihilating or capturing the core of the Southern resistance - elite units of our frontline fighters along with the civilian and much of the military leadership. A month later, at the end of April, the US and
Army of the Republic of Vietnam (ARVN) tried again. The initial ARVN attack of the
Cambodian Campaign was launched by ARVN and US ground forces, which attempted to "clean out the sanctuaries". PAVN/NLF forces, however, had already been evacuated on March 19. COSVN and its sub-divisions had already withdrawn to the
Kratié area and successfully avoided destruction. A marked reduction in radio traffic and transmitter power also made them difficult to place accurately at their new location, despite close 24-hour monitoring. The military benefits and tragic repercussions of the bombing and invasion have been contentious subjects. Westmoreland thought that it was "unfortunate" that Nixon had announced the capture of COSVN as one of the primary objectives of the Cambodian operations. Members of the COSVN generally agree, but view the long-term political advantage gained as being worth the cost of the evacuation. =="Bamboo Pentagon"==