WITH U.S. TROOPS, SAUDI ARABIA, NOV. 19 -- For the second straight day, heavy seas today wiped out a key part of a U.S. mock amphibious assault widely seen as a practice run for an invasion of Kuwait.

Wind-whipped swells up to 14 feet high stopped the launching of hovercraft to ferry U.S. Marines to the beach, said Navy spokesman James Taylor. The hovercraft can work in seas up to 12 feet, another spokesman said.

As part of the amphibious assault the U.S. military calls Exercise Imminent Thunder, up to 800 Marines were supposed to storm a beach by hovercraft and helicopter, then establish a beachhead as a base for future war games.

Sunday, about 400 Marines were flown ashore by helicopter but the rest stayed aboard ships about 20 miles off the Saudi coast because of swells up to 10 feet high.

The Navy had hoped the sea would be calm enough today for another try with the hovercraft but when the Navy reported high seas again, the operation was canceled altogether.

Taylor said it was called off to protect both the Marines and the hovercraft. "In an exercise, why take unnecessary risks?" he asked.