719, that process accelerated. Hanoi's effort was simplified by the fact that the Royalist forces in the south had little experience fighting PAVN and they were quickly overwhelmed. Inept and ineffective were terms utilized to describe their defense. On 30 April 1971 the key town of Attopeu was seized by the PAVN. Vang Pao himself was not blind to the realities facing his people. He had threatened to launch a mass migration of the Hmong to Thailand on three previous occasions. In November 1969, he tried a different tack, contacting the Pathet Lao and attempted to negotiate a quid pro quo: the Hmong would cease fighting if the communists would allow them to establish a semiautonomous state in Xieng Khouang Province. The diminishing number of troops available to Vang Pao demanded their replacement by growing numbers of Thai volunteers (Project Unity), who increasingly took over the ground war in the north. By the end of 1971, the entire 55-man battalion of Thais were in action, whose total numbers were 6,000–8,000 men. During the following year, those numbers had ballooned to 17,800. The total force eventually deployed was three artillery and 27 infantry battalions. Withdrawal (1972–1973) Talking and fighting By October 1971 Prince Souvanna had little alternative but to accept the Pathet Lao program as the basis for negotiations. The Pathet Lao agreed to the new negotiating effort and on 14 October, representatives of the party arrived in Vientiane. Two weeks later they were followed by Phoumi Vongvichit, secretary general of the Pathet Lao. Communist demands included: a cessation of the U.S. bombing of Lao territory; withdrawal of all U.S. advisors and military personnel; an election for a new National Assembly; the establishment of a coalition government; and compensation and resettlement for those Lao who had been forcibly relocated would be undertaken. The pace of negotiations in Laos, however, mirrored those in South Vietnam, the impetus of which was determined by the perceived military success of the protagonists. The dreaded PAVN wet season offensive (Campaign Z) began on 17 December 1971. The multi-division offensive was commanded by Major General Lê Trọng Tấn, who had commanded the PAVN counteroffensive against Operation Lam Son 719. Once again the PAVN rolled across the Plain of Jars and to the outskirts of Long Tieng. This time however, they had brought along a battery of 130mm artillery, which proceeded to pummel the defenders. By 17 January