Learn more about Cambodian Incursion
|Part of the Vietnam War|
May 1970 cover of Time magazine.
| Image:Flag of South Vietnam.svg Republic of Vietnam (RVN)|
Image:Flag of the United States.svg United States (U.S.)
| Image:FNL Flag.svg National Front for the Liberation of South Vietnam (Viet Cong)|
Image:Flag of North Vietnam.svg Democratic Republic of Vietnam (North Vietnam)
| Image:Flag of South Vietnam.svg 40,000,|
Image:Flag of the United States.svg 30,000
| Image:Flag of South Vietnam.svg 800 dead,|
Image:Flag of the United States.svg 284 dead,
| 11,349 dead,|
|Ap Bac – Binh Gia – Song Be – Dong Xoai – Ia Drang – Long Tan – Dak To – Tra Binh Dong –Ong Thanh – 1st Tet – Khe Sanh – 1st Saigon – Lang Vei – Hills 881 & 861 – 2nd Tet – Hamburger Hill – Binh Ba – Ripcord – FSB Mary Ann – Easter '72 – An Loc – Kontum – Phuoc Long – Ho Chi Minh – Buon Ma Thuot – Xuan Loc – 2nd Saigon – Barrell Roll – Rolling Thunder – Pony Express – Steel Tiger – Commando Hunt – Linebacker I – Linebacker II – Chenla I – Tiger Hound – Lima Site 85 – Tailwind – Chenla II – Cambodia|
The Cambodian Incursion was a military campaign during the Vietnam War that culminated in a limited-objective invasion of Cambodia in 1970. The campaign was known officially in the U.S. Army as the Sanctuary Counteroffensive. U.S. incursions into Cambodia began in 1965 with numerous tactical bombings which thereafter were escalated into an intensive carpet bombing campaign that took place from May 1 to June 29,1970 and were overlapped by the 75-day South Vietnamese incursion occurring April 29 to July 22. A total of 13 major operations were conducted by the allies during the campaign. Only three of these involved U.S. ground forces, but all or parts of the 1st Cavalry Division (Airmobile), 4th Infantry Division, 25th Infantry Division, U.S. 199th Light Infantry Brigade, 3rd Brigade (Separate) 9th Infantry Division, and 11th Armored Cavalry Regiment conducted combat operations inside Cambodia.
 Historical background
The National Liberation Front and their North Vietnamese allies had used large sections of Cambodia along its border with Vietnam as sanctuary areas into which they could withdraw to avoid destruction, rest and rehabilitate units without being attacked by allied forces, and as base areas in which materiel could be stored on a large scale. North Vietnamese began moving through Cambodian territory in 1963. In 1965, the government of Cambodia concluded a secret agreement with North Vietnam that allowed for permanent bases in Cambodian soil and the use of Cambodian ports for supply. In spite of these agreements, the government of Cambodia claimed to be neutral.
In 1968, The Khmer Rouge lauched a national insurgency to overthrow the government. While they received limited material help from North Vietnam at the time, they were able to shelter their forces in areas controlled by Vietnamese troops.
Between 1965 and March 1969 the United States and South Vietnam made more than two thousand incursions into Cambodian territory that were backed by primarily tactical bombing operations, despite Cambodia's claims of neutrality. Thereafter commander of the Military Assistance Command, Vietnam (MACV), General Creighton Abrams, recommended to newly-inaugurated President Richard Nixon, that the base areas be attacked by aerial bombardment using B-52 bombers. Nixon authorized the campaign, which totalled more than 3000 sorties over 14 months.
Sihanouk went abroad in January, 1970, for an extended tour involving visits to communist countries and a stay in France. Sihanouk directed in March that his ministers organize anti-Vietnamese demonstrations as a way of pressuring the communists he was negotiating with. The demonstrations quickly got out of control. Unrest in Cambodia spurred an ultimatum to the North Vietnamese to withdraw its forces from Cambodia.
On March 18, Premier Lon Nol and the National Assembly deposed Sihanouk. Lon Nol did not have the active support of the army at the time. The National Assembly named him as a provisional head of state. This immediately led to Sihanouk relocating to China and establishing himself as the figurehead leader of the Khmer Rouge. Sihanouk lent his name and his popularity in rural areas of Cambodia to the Khmer Rouge movement. Combined with the actions of the North Vietnamese, who were supplying large amounts of weapons to the Khmer Rouge, the country plunged into civil war. Sihanouk lent his full support to the Khmer Rouge even though he had no authority over their organization and little influence on them. When the port of Sihanoukville shut down military supplies, the North Vietnamese Army reacted with military force. The NVA launched a campaign against the Cambodian Army westward from its base areas toward Phnom Penh, isolating and overrunning or besieging a number of Cambodian cities including Kampong Cham.
The South Vietnamese responded on March 27 with a covert raid by an ARVN ranger battalion to overrun an NVA base camp three kilometers inside Cambodia, as a rehearsal for future operations and to test public reaction in the United States. Lon Nol requested military assistance from the United States government on April 14.
That same day the ARVN conducted the first of three brief cross-border operations under the aegis of Operation Toan Thang ("Complete Victory") 41, sending armored cavalry units into regions of Cambodia's Svay Rieng Province nicknamed the "Angel's Wing" and the "Crow's Nest" (from their perceived shapes on maps). These were largely reconnaissance missions in preparation for a more wide scale incursion being planned by MACV and its ARVN counterparts, subject to authorization by Nixon. On the evening Of April 26 Nixon gave his approval, with the stated goals of (1) reducing allied casualties in South Vietnam, (2) assuring the continued withdrawal of U.S. forces from Vietnam, (3) allowing Vietnamization to proceed on schedule, and (4) to enhance peace negotiations.
 Incursion operations
The bombardment of Cambodia began in 1965 as the Johnson administration commanded primarily tactical bombing in support of more than two thousand ground incursions by the CIA and US Special Forces. From 1965 to 1968 US planes flew 2,565 sorties dropping 214 tons of bombs. Beginning March 18, 1969, with the launch of the Menu Campaign, the Nixon administration escalated the incursion into a massive carpet bombing campaign that would see American forces drop 2,756,941 tons of bombs on Cambodia until Congress imposed an end to the bombing in August 1973. The total tonnage dropped exceeded that dropped by the combined Allied forces during World War II, including the bombs dropped on Hiroshima and Nagasaki.http://migs.concordia.ca/links/documents/Bombs_over_Cambodia_Kiernan.pdf
The Menu Campaign began on April 29, 1970, with Operation Toan Thang 42, in which 12 ARVN battalions and 8,700 troops crossed into the Angel's Wing under the command of General Do Cao Tri, the commander of III Corps Tactical Zone and by reputation the most aggressive and competent ARVN general.
On May 1 an even larger operation, known by the ARVN as Operation Toan Thang 43 and by MACV as Operation Rockcrusher, got underway with 8 US and 6 ARVN battalions entering Cambodia. Known as Task Force Shoemaker, the force attacked the "Parrot's Beak" area of Svay Rieng province with 10,000 U.S. and 5,000 South Vietnamese troops under the operational control of the 1st Cavalry Division, using mechanized infantry and armored units to drive deep into the province and link up with ARVN airborne and U.S. airmobile units lifted in by helicopter.
In the first week of operations additional battalion and brigade units were committed, so that between May 6 and May 16, a total of 90,000 allied troops (including 33 U.S. maneuver battalions) conducted search operations in the sanctuaries:
- Operation Bold Lancer (Toan Thang 44), 1st Brigade 25th Infantry Division, May 6-May 16
- Operation Tame The West (Binh Tay 1), 2nd Brigade 4th Infantry Division; May 6-May 14 in northeastern Cambodia
- 3rd Brigade 1st Cavalry Division, May 6-June 25, in "the Belly" area north of An Loc.
- Operation Binh Tay (1,2,3, and 4), 22nd ARVN Division, May 6-June 26 northeastern Cambodia
Almost immediately units, facing largely disorganized resistance, overran large NVA supply bases. These successes, coupled with a violent political upheaval on American college campuses in protest of the incursion, caused Nixon on May 7 to issue a directive limiting American incursion in Cambodia to a depth of 30 kilometers (21.7 miles) and setting a deadline of June 30 for withdrawal of all U.S. forces there.
Seizures of large NVA base areas became well-publicized events, notably "the City" near Snuol, captured on May 5 and containing 182 supply caches, "Rock Island East" on May 8 and containing 28 caches, and "Shakey's Hill" on May 23, all by the 1st Cavalry Division and its attached mechanized units.
U.S. sweeps were conducted by individual companies in dense jungle, resulting in frequent small unit firefights. However most large NVA units, including headquarters units, fled deeper inside Cambodia to remain out of contact, although they were only able to move a small amount of materiel before it could be seized (approximately 400 tons out of a total of more than 10,000 tons).
The South Vietnamese were not constrained by the time and geographic limitations placed upon U.S. units. From the provincial capital of Svay Rieng the ARVN pressed westward to Kampong Trabec, where on May 14 their 8th and 15th Armored Cavalry regiments defeated the 88th NVA Regiment. On May 23, the South Vietnamese pushed inward beyond the deepest US penetrations and attacked Krek. On May 25 ARVN cavalry units surrounded and destroyed the 272nd NVA Regiment at the Chup Rubber Plantation, and on May 29 lifted the siege of Kompong Cham. The last major battle of Toan Thang 42 was again at Chup, where the 271st NVA Regiment was defeated by ARVN mechanized forces, rendering the NVA 9th Division comb at ineffective. The ARVN remained in Cambodia until July 22 conducting road security.
Militarily the Cambodian Incursion achieved its objectives and was successful in destroying a large amount of war material in the area by means of an unprecendent bombing campaign. The operation was successful in destroying the military effectiveness of North Vietnam in the southern parts of South Vietnam. The combined loss of the Cambodian ports and the tons of supplies crippled operations in the area for a long time and assisted in the policy of turning the war over to South Vietnam. For many U.S. units, combat in Cambodia was the last significant action any of them experienced for the next six months, by which time the 4th, 9th and 25th Divisions were completing the process of returning to the United States.
Politically the incursion increased domestic unrest in the United States. The American media and many commentators claimed that the incursion had violated Cambodia's neutrality and had drawn it into the war. Those who supported the war argued that the criticism of the incursion was often difficult to reconcile with the obvious military presence of North Vietnam's Army in Cambodia. The unrest led to violence with the worst violence being the Kent State shootings in Ohio on May 4. Reaction in the United States Congress led to legislative attempts to limit executive power, beginning with the Cooper-Church amendment on June 30, barring further spending of funds for military operations in Cambodia without congressional approval.
 Statistical summary
For the period of October 4, 1965 to August 15, 1973:
- Total sorties: 230,516 (on 113,716 sites)
- Total tonnage dropped: 2,756,941 tons
- percentage of bombing that was indiscriminate: 10%
- estimated number of Cambodian civilians killed: more than 150,000 
For the period May 1 to June 30, casualties were:
- U.S.: 284 dead; 2,339 wounded; 13 missing
- ARVN: 800 dead; 3,410 wounded
- NVA/VC: 11,349 dead; 2,328 captured
600 supply caches were captured and their material removed or destroyed:
- 22,892 individual weapons
- 2,509 crew-served weapons
- 15 million rounds of small arms ammunition
- 199,552 rounds of anti-aircraft ammunition
- 143,000 rounds of rocket, mortar, and recoilless rifle ammunition
- 62,022 hand grenades
- 5,482 land mines
- 1,002 demolition charges
- 41 tons of explosives
- 55 tons of medical supplies
- 435 motor vehicles
- 7,000 tons of rice
- Nolan, Keith, Into Cambodia: Spring Campaign, Summer Offensive, 1970, (1990)
- Stanton, Shelby, U.S. Army and Allied Ground Forces in Vietnam Order of Battle, (1978)
- Starry, Donn (Gen, USA ret.), Vietnam Studies: Mounted Combat in Vietnam, (1978)
- Tolson, John (LtGen, USA ret.), Vietnam Studies: Airmobility 1961-1971, (1973)
- Short, Philip Pol Pot: the history of a nightmare (2004)