The visitors from China seemed innocuous enough. The five of them had flown in from Beijing to attend the 1989 American Physical Society Conference on Shock Waves in Condensed Matter in Albuquerque, New Mexico. Danny Stillman, director of the technical intelligence division at Los Alamos National Laboratory, met the visitors' plane, took care of their transportation and food needs, and escorted them through the National Atomic Museum in Albuquerque. All five visitors seemed to be jolly academic tourists, but appearances can be—and in this case were—deceptive. In the next year or two, all five were revealed to be top scientists in the Chinese Academy of Engineering Physics, the equivalent of the combined US nuclear weapons laboratories at Los Alamos, Livermore, and Sandia. Those visitors from China were scouting the American turf.
In June of 1988, another guest traveled to Los Alamos by himself: Yang Fujia was a multitasking Chinese technocrat with an ill-defined agenda. (In China, family names come first, and I will observe that custom in the material that follows. The professor's family name is Yang; Fujia is the equivalent of "Tom.") Besides serving as the director of the Shanghai Institute of Nuclear Research, Yang held positions at Fudan University and in several international scientific bodies. Stillman welcomed Yang's visit, for he had learned that the best source of intelligence was often simple and direct questions posed to a knowledgeable visitor.
For starters, Stillman asked the professor, "Does the Chinese nuclear weapons program have a prompt burst reactor?" Such an experimental reactor, typically located in a remote area, can operate supercritically for a fraction of a second and thereby simulate the efflux of radiation and particles from a nuclear detonation. Yang's answer: "Of course."