Over a few hours under gray skies, dozens of combat planes and helicopters roar on and off the flight deck of the aircraft carrier USS Nimitz, in a demonstration of U.S. military power in some of the world's most hotly contested waters.

MH-60 Seahawk helicopters and F/A-18 Hornet jets bearing pilot call signs like "Fozzie Bear," "Pig Sweat" and "Bongoo" emit deafening screams as they land in the drizzle on the Nimitz, which is leading a carrier strike group that entered the South China Sea two weeks ago.

The group's commander, Rear Adm. Christopher Sweeney, said the tour was part of a U.S. commitment to uphold freedom of passage in the waters and airspace of a region vital to global trade.