Additionally , technical problems arose that appeared to make the Zeus almost trivially easy to defeat . One problem , discovered in tests during 1958 , was that nuclear fireballs expanded to very large sizes at high altitudes , rendering everything behind them invisible to radar . This was known as '' nuclear blackout '' . By the time an enemy warhead passed through the fireball , about above the base , it would only be about eight seconds from impact . That was not enough time for the radar to lock on and fire a Zeus before the warhead hit its target
tests during 1958
Operation Hardtack I
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