Underground nuclear weapons testing: Despite improvements in simulation techniques, weapons designers defend their need for `live¿ testing to help maintain the US. nuclear deterrent

Beneath a stretch of mesas and bone-dry lake beds some 100 miles north of Las Vegas, Nev., at least 16 nuclear warheads were detonated last year, releasing enough energy to destroy a dozen major cities. Since 1951 the United States has exploded more than 680 bombs above and below this landscape, broken only by clumps of sagebrush, scraggy grass, and craters.