Operation Flintlock (nuclear test)

The United States's Flintlock nuclear test series was a group of 47 nuclear tests conducted in 1965–1966. These tests followed the Operation Whetstone series and preceded the Operation Latchkey series.

Duryea
Following emplacement of the Duryea nuclear device and stemming of the shot hole, several instrument cables failed and a plan was devised to repair them. A shaft designated U20a1 was drilled 18 m southwest of the original emplacement hole designed U12a, to a depth of 149 m, and then a tunnel between U12a and U12a1 was constructed, allowing for repair of the cables.