A year after the North Carolina accident, a SAC ground crew removed four Mark 28 bombs from a B-47 bomber and noticed that all of the weapons were armed. But the seal on the ready/safe switch in the cockpit was intact, and the knob hadn’t been turned to GROUND or AIR. The bombs had not been armed by the crew. A seven-month investigation by Sandia found that a tiny metal nut had come off a screw inside the plane and lodged against an unused radar-heating circuit. The nut had created a new electrical pathway, allowing current to reach an arming line—and bypass the ready/safe switch.