Complex sentence: Both Atolls were part of the US Pacific Proving Grounds, however, the extremely high yields of the Castle weapons caused concern within the AEC that potential damage to the limited infrastructure already established at Eniwetok would delay other operations.
Split into simpler sentences: Both Atolls were part of the US Pacific Proving Grounds. However, the extremely high yields of the Castle weapons caused concern within the AEC that potential damage to the limited infrastructure already established at Eniwetok would delay other operations.