Security officials have considered using British military personnel to repatriate forcibly thousands of hard-core Vietnamese. Elsewhere in the region, the military option has proved successful in returning boat people, but Hong Kong and Britain have been reluctant to use such means for fear of international criticism. The most suitable vessels are based in Britain, a senior official said, and the Ministry of Defence would not allow Royal Navy personnel to take part in deportations. The official said the risk of transporting large numbers by sea for at least two days was greater than an hour's flight. Instead, the authorities will switch next month to using chartered Boeing 747s instead of the smaller McDonnell Douglas DC-10s that have been provided by Continental Micronesia. It is understood the airline will also provide the jumbo jets. Hong Kong has to transfer huge numbers of Vietnamese with about 18,000 left in the camps who must be returned, according to orders from China, before the handover.