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Dung's Cambodian campaign began with a series of air strikes on border forces that softened Khmer Rouge defense lines. This was followed by punishing attacks that killed an estimated 17,000 Kampucheans. The ferocity convinced observers that something big was building, but the best guess was that Hanoi was after no more than the eastern third of its neighbor. In early November, Viet Nam signed a 25-year friendship treaty with the Soviet Union. The accord was accompanied by talks between Dung and Soviet Defense Minister Dmitri Ustinov, who agreed in private that the regime of Cambodian Leader Pol Pot had to be destroyed.
Returning home, Dung moved twelve Vietnamese divisions into jump-off positions in Viet Nam and Laos. Air support and logistics were organized. The wavering draftees who had failed in the previous attack were replaced with veteran soldiers.
Finally on December 14 Dung sent two divisions from Tay Ninh over the border northward through the Fishhook section of Kampuchea in a run on the town of Kratie. The maneuver was meant to lure the Kampuchean Communists into assuming that the Vietnamese were gathering for no more than a limited operation. The ruse worked perfectly; the Cambodians were drawn northeastward.
Two weeks later, on Christmas Day, Dung launched his offensive. From Can Tho in the south, elements of two Vietnamese divisions rolled to interdict Cambodian Highways 3 and 4. Capturing the town of Takeo, they moved onward toward Phnom-Penh itself. Two more divisions of about 10,000 men moved out of Tay Ninh, bound for the Mekong Riverside town of Kompong Cham and for the capital. Another division slid in parallel fashion across the Parrot's Beak salient at the border to outflank Cambodian forces between Highways 1 and 7. From Pleiku three additional divisions moved out to attack in the north around the town of Stung Treng. At the same time, Vietnamese troops reportedly stationed in Laos poured south along the Mekong to engage the Khmers.
The attack was an instant success all along the line. The armored divisions captured their objectives except Kompong Som with little difficulty. In an assault on Kompong Cham, the Vietnamese used Soviet pontoon bridges to move an entire mechanized division across the Mekong River. This broke the back of the Khmer defense; 6,000 Khmer troops suddenly found themselves wedged between the onrushing Vietnamese and the Mekong.
The Vietnamese hardly stopped for fuel before they rolled again. Thundering northwest on Highways 5 and 6 in the Nebraska-flat rice-growing area of western Cambodia, they toppled the provincial capitals of Battambang, the country's second city, and Siem Reap, near the temple ruins at Angkor Wat.
By last week the Vietnamese blitzkrieg controlled almost every important town and every major highway in Cambodia. The victorious invaders had also captured some strange spoils of war. In Phnom-Penh they found crates containing ten MiG airplanes; the jets had been a gift of the Chinese, but since no Kampuchean pilot knew how to fly them, the MiGs had never been uncrated.