HONOLULU - A retired Coast Guardsman who's an expert on sea emergencies says the 12 Marines aboard two helicopters that crashed off Hawaii have a lot to overcome.

Mario Vittone was a helicopter swimmer and Marine accident investigator with the Coast Guard. He says the crash would have happened very quickly. The Marines would have had to survive the crash, then the on-rushing of water, followed by dehydration and exposure to the elements.

Two helicopters each carrying six Marines went down off Oahu's north shore late Thursday. On Saturday, officials expanded the search area to the island's west coast.

Vittone says expanding the search area lowers the probability of detection.

Rescuers have been searching round-the-clock. The Coast Guard says there's no intention as of Sunday morning to call off or suspend the search just yet.