In the early 1970s the North Vietnamese leaders resorted to various methods of forced assimilation. At first they sought to pressure ethnic Chinese to adopt Vietnamese citizenship, but only a handful of Hoa cadres complied, most of whom were heavily assimilated individuals anyway. Thereupon the authorities attempted to seize the Chinese passports of the ethnic Chinese under various pretexts, but most Hoa refused to give up their passports. The regime made repeated efforts to transform the Chinese minority schools into mixed Chinese-Vietnamese schools in which Hoa children were to study together with Vietnamese pupils and the curriculum was to be based on the standard North Vietnamese curriculum. The authorities ceased to hire Hoa interpreters, nor did they employ Hoa in offices that were in regular contact with foreigners. Ethnic Chinese were rarely admitted to the military, and even if they volunteered for service, they could serve only in logistical units but not in troops sent to the front in South Vietnam. Following the Battle of the Paracel Islands (a Chinese action that Hanoi disapproved), the DRV authorities started to hinder the Hoa in visiting their relatives in the PRC.