During the tumultuous years that followed in China, "Isabel" served as a member of the patrol and as its flagship, charged with protecting American commerce from pirates. Based at Shanghai, "Isabel" spent the low-water period on the river at Hankow, returning to the coast in the summer. She and the other small gunboats of the U.S. Navy in China performed the arduous task of protecting American interests during numerous incidents and threats to American nationals. On many occasions the ship came under fire, as in October 1926 when she was caught between the rifle fire of opposing Chinese armies on the Yangtze. "Isabel" also took part in the Nanking Incident on 24 March 1927, when shelling and threats of force procured the release of a large group of American and British prisoners held by Chinese nationalists in Nanking. She patrolled the 1,700 nautical miles (3,148 kilometers) of this dangerous river until 1928, when enough purpose-built river gunboats had arrived to serve in the Yangtze Patrol that she was no longer needed on the river. She then joined the Asiatic Fleet.