Download coordinates as: The United States's Flintlock nuclear test series[1] was a group of 47 nuclear tests conducted in 1965–1966.

These tests [note 1] followed the Operation Whetstone series and preceded the Operation Latchkey series.

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 metres (59 ft) southwest of the original emplacement hole designed U12a, to a depth of 149 metres (489 ft), and then a tunnel between U12a and U12a1 was constructed, allowing for repair of the cables.

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