BEIJING—The U.S. Navy said an American underwater drone that had been in China’s hands for five days would be examined for any tampering, but appeared intact, as U.S. officials attempted to fathom Beijing’s motives for the unusual incident in the South China Sea.

Photographs released by the U.S. naval forces in the Pacific late Wednesday show the “ocean glider” drone being loaded onto the USS Mustin, a guided-missile destroyer, following a handover from the Chinese ship on Tuesday.

“The...