"A Marine Corps CH-53E Super Stallion helicopter from 3rd Marine Aircraft Wing crashed in the vicinity of El Centro, California, at approximately 2:35 p.m. [7:35 p.m. GMT] Tuesday during a routine training mission," the release said. "The status of all four [crew members] is presumed dead pending positive identification. The cause of the crash is currently under investigation."
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The names of the victims will be released within the next 24 hours after their families are notified, the statement added.
The Sikorsky CH-53E Super Stallion is the largest and heaviest helicopter in the United States military.