First Battle of Lang Son

The First Battle of Lang Son was fought during the Sino-Vietnamese War, days after the Chinese advanced 15 to 20 kilometers deep into the northern provinces of Vietnam. The fighting occurred primarily at the city of Lạng Sơn, few kilometers from the Sino-Vietnamese border. Although the Chinese eventually occupied Lạng Sơn and its nearby vicinities during the battle, it proved during that time that the Chinese regular units invading northern Vietnam are no match against militia and irregular Vietnamese units tenaciously harassing the Chinese advance southwards towards Hanoi, Vietnam's capital city, and eventually took the Chinese forces days to occupy the city and dislodge its defenders.

Background
As part of the punitive expedition against Vietnam for the occupation of Chinese-supported Democratic Kampuchea, Chinese forces entered northern Vietnam and advanced quickly about 15–20 kilometers into Vietnam, with fighting mainly occurring in the provinces of Cao Bằng, Lào Cai and Lạng Sơn. The Vietnamese avoided mobilizing their regular divisions into the fighting to use most of them for the defense of Hanoi. The Vietnamese forces tried to avoid direct combat, and often used guerrilla tactics to harass the Chinese forces advancing southwards. To make this work for the Vietnamese, they had to use their mountainous terrain to their advantage, which was a serious handicap for the Chinese trying to assault and destroy several Vietnamese irregular units fighting on the frontlines.

The battle
The initial Chinese advance in northern Vietnam soon lost its momentum, and a new wave of attack was sent in. Eight Chinese divisions joined the battle, and captured some of the northernmost cities in Vietnam. After capturing the northern heights above Lạng Sơn, the Chinese surrounded and paused in front of the city in order to lure the Vietnamese into reinforcing it with units from Cambodia. This had been the main strategic ploy in the Chinese war plan as Deng did not want to risk an escalation involving the Soviets. The VPA high command, after a tip-off from Soviet satellite intelligence, was able to see through the trap, however, and committed reserves only to Hanoi.

Once this became clear to the Chinese People's Liberation Army, the war was practically over. An assault was still mounted, but the Vietnamese only committed one VPA regiment defending the city. After three days of bloody house-to-house fighting, Lạng Sơn fell on March 6. The PLA then took the southern heights above Lạng Sơn and occupied Sapa. Even though the PLA claimed to have crushed several of the Vietnamese regular units, the reality was that regular Chinese units only engaged border and regional Vietnamese militia units, which proved more than a match for regular Chinese units.

Aftermath
A temporary pause occurred after the battle after the Chinese suffered heavy losses, but fighting in northern Vietnam is still clinging, growing tenaciously as the Chinese marched further south. Then there is a resumption of Chinese attacks aimed at the major provincial capitals and key communication centres in the border hinter land. Major battles developed at Cao Bằng, Lạng Sơn, Hoang Lien Son, Lai Châu and Quảng Ninh. The Chinese again suffered heavy losses from these battles, but they declared that the road to Hanoi was now open, and, believing that victory was already theirs, the Chinese withdrew from Vietnam back towards the Sino-Vietnamese border, marking the conclusion of the war.