An Army UH-60 Black Hawk helicopter went down Tuesday night during a training exercise about 2 miles off the Hawaiian island of Oahu, according to the US Coast Guard.
Responders are searching for five missing crewmen.
The aircraft went down off the largely uninhabited Kaena Point on the west side of the island.
Two Black Hawk air crews were training between Kaena Point and Dillingham Airfield, a few miles east, when communications were lost, the Coast Guard said.
Three helicopters, a Coast Guard cutter, a response boat and the Honolulu Fire Department were among those responding.