Five hundred pounds of plastic explosive sent this 32,000-ton aircraft carrier to the bottom of the Gulf of Mexico in May, forming the largest intentional man-made reef in history and marking the inauguration of a Navy program to turn old ships into coral reefs. To meet EPA standards for sea disposal, the 888-foot carrier was stripped of oil, paint and asbestos, at a cost of $8 million. It worked: The scuttle didn´t even leave a slick on the surface. The hull of the craft now rests at 212 feet, too deep for casual scuba divers, though the higher superstructure should be fair game. You have plenty of time to plan your trip-the Oriskany won´t disintegrate for hundreds of years.