 The fireball of the conventional explosion was visible from Alamogordo Army Air Field 60 miles (97 km) away, but there was little shock at the base camp 10 miles (16 km) away. Shields thought that the explosion looked "beautiful", but it was hardly felt at 15,000 feet (4,600 m). Herbert L. Anderson practiced using a converted M4 Sherman tank lined with lead to approach the 5-foot (1.5 m) deep and 30-foot (9.1 m) wide blast crater and take a sample of dirt, although the radioactivity was low enough to allow several hours of unprotected exposure. An electrical signal of unknown origin caused the explosion to go off 0.25 seconds early, ruining experiments that required split-second timing. The piezoelectric gauges developed by Anderson's team correctly indicated an explosion of 108 tons of TNT (450 GJ), but Luis Alvarez and Waldman's airborne condenser gauges were far less accurate.
