Andrew Dang
Interested in the Sino-Vietnamese War of 1979Dec 5

During 1979 Sino-Vietnamese conflict why did China decide to withdraw
their troops when the road to Hanoi lay open and the city could have
fallen to China?
In short answer, during the Sino-Vietnamese War, after suffering a large
number of casualties and before the coming of the Vietnamese crack
troops, the Chinese People’s Liberation Army (P.L.A) had to withdraw
their forces. The “road to Hanoi lay open and the city could have fallen
to China” was also a war myth. In fact, all the roads from the border
regions to Hanoi were heavily fortified and garrisoned by several main
force divisions of the People’s Army of Vietnam (P.A.V.N).

Chinese POWs of the 448th Regiment at the Sino-Vietnamese War, March 1979.

During only one month of the Sino-Vietnamese War of 1979, the P.L.A
suffered a total of 31,212 casualties, in which a total 7,915 Chinese
troops lost their lives. The total Chinese casualties were roundly 10%
of the invading forces of 200,000 to 300,000 men at beginning of the
war. Specifically, the Guangzhou Military Region suffered 5,103 dead and
15,412 injured, the Kunming Military Region also suffered 2,812 killed
and 7,886 wounded.

(Xiaoming Zhang, “Deng Xiaoping's Long War: The Military Conflict
between China and Vietnam”, 2015, p. 119)

An abandoned Chinese tank at Cao Bằng Province. Photographed by Trần
Mạnh Thường, February 1979.

On the other hand, the Chinese armored forces also suffered from high
casualties. According to the Vietnamese war statistics, from 726 Chinese
tanks and armored personal carriers at the beginning of the war, around
550 of them were either destroyed or out of the service. The Western
sources also believed that several hundred Chinese tanks were damaged,
destroyed or abandoned during the course of the war.

A Chinese tank was destroyed by Vietnamese troops during the
Sino-Vietnamese War. Photographed by Trần Mạnh Thường, 17 February 1979.

The Battle of Lạng Sơn (17 February – 16 March 1979) or the biggest
battle of the Sino-Vietnamese War clearly exposed the weaknesses of the
Chinese forces, as it took not one but 16 days of heavy fighting. The
P.L.A also suffered at least 1,271 killed and 3,779 wounded during the
battle. Henceforth, the initial plan of the P.L.A in order to encircle
all of the Vietnamese divisions around Lạng Sơn and “opened the gate” to
Hanoi in just one week fell miserably:

“For instance, Deputy Defense Minister Su Yu reported to the 3rd Plenum
of the CCP in late December 1978 that the P.L.A could take Hanoi in one
week with only partial strength from the Guangzhou and Kunming Military
Regions. In fact, it took the P.L.A 16 full days to capture Lang Son (85
miles to Hanoi) with a strength of 10 divisions drawing from six
military regions-a strength almost as much as that of the Guangzhou and
Kunming MR's combined.”

(King C. Chen, “China’s War Against Vietnam, 1979: A Military Analysis”,
1983, p. 27)

Map: the positions of the P.A.V.N divisions during the Sino-Vietnamese War.

Meanwhile, the city of Hanoi was not “lay open” but it was strongly
fortified and garrisoned by the crack troops of the 308th Infantry
Division. The road from Lạng Sơn to Hanoi was more than 100 kilometres,
but it was densely garrisoned by numerous main force divisions of the
P.A.V.N. For example, around the town of Lạng Sơn, they were the regular
troops of the 3rd Infantry Division (“Yellow Star Division”) and the
regional forces of the 327th and 337th Infantry Divisions. Meanwhile,
the 308th, 312th, and 390th Divisions were deployed by the P.A.V.N along
the roads from Lạng Sơn to Hanoi.

A Vietnamese artillery unit during the Sino-Vietnamese War of 1979.

The Vietnamese People’s Air Force (V.P.A.F) with several hundreds of
MIG-17s, MIG-21s, F-5s and A-37s were ready to bombard the Chinese
positions. Meanwhile, in early March 1979, the P.A.V.N also deployed the
crack units of the 304th, 306th and 325th Infantry Divisions at the
second line of defensive system. All of them were the main force
divisions of the 2nd Corps which had just came back from the Cambodian
front.

Vietnamese troops of the 2nd Corps waiting for the transportation to the
front.

Furthermore, the BM-21 "Grad" as the deadly Soviet truck-mounted 122 mm
multiple rocket launchers were successfully deployed on the front. The
Rocket Artillery Regiment or the 204th Regiment with several BM-21
"Grad" launchers also gathered at Cai Kinh (Hữu Lũng District, Lạng Sơn
Province), planning to rain down their fires on the Chinese forces at
the beginning of March 1979. However, on 5 March 1979, the P.L.A
announced the military withdrawal from Vietnam, so the rocket artillery
attack against the Chinese forces was subsequently postponed.

In conclusion, it could be seen that the high casualties of war, the
destruction of the Chinese armored forces during the border battles, the
heavily fortified areas from Lạng Sơn to Hanoi as well as the deployment
of the main force divisions of the P.A.V.N were the main reasons why
China decide to halt their offensive toward the city of Hanoi. Once
again, many thanks for reading my answer and best regards,

Andrew

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