It is called a research center, but the Pakistan Institute of Nuclear Research looks more like a fortress. Layers of barbed wire surround the sprawling complex in the dusty hills at Kahuta, 20 miles southeast of Pakistan's capital, Islamabad. Much of the facility is buried beneath the earth, a precaution against accident -- or perhaps surprise attack. Paratroopers guard the installation, and tanks block all routes into Kahuta. Crotale surface-to- air missiles and antiaircraft guns bristle toward the skies, through which Pakistani air force planes fly round-the-clock patrols. Unauthorized entry to Kahuta is impossible, sightseeing in the vicinity ill advised.
Precise...