Underway on 29 April, "Benner" first proceeded to Eniwetok Atoll in the Marshall Islands. There, she participated in "Operation Hardtack I" — a 35-detonation series of atmospheric nuclear tests designed to evaluate new types of weapons, the effects of high-altitude explosions, and the new Polaris missile warhead prototype. "Benner"s assignments during these tests included weather observations, search and rescue, and scientific equipment recovery. She also performed air operations center functions at Bikini Atoll. The destroyer then departed Eniwetok on 1 August and arrived in Yokosuka five days later.