The Sand Pebbles was the nickname for a fictional gunboat, USS San Pablo. All gunboats in the Navy were named for islands. The movie dramatized the Yangtze Patrol during the period just before World War II, but the movie does not include the evacuation on Nanking and the attack on the Panay.
Thanks for the update. I had forgotten the definite historical details (or lack thereof) only remembering the crew was on the Yangtze in the early part of the 20th century.