The Spanish boats were replaced in the 1920s by and were the largest, and next in size, and and the smallest. China in the first fifty years of the 20th century, was in low-grade chaos. Warlords, revolutions, natural disasters, civil war and invasions contributed. Yangtze boats were involved in the Nanking incident of 1927 when the Communists and Nationalists broke into open war. The Chiang Kai-shek's massacre of the Communists in Shanghai in 1927 furthered the unrest, U.S. Marines with tanks were landed. River steamers were popular targets for both Nationalists and Communists, and peasants who would take periodic pot-shots at vessels. During the course of service the second protected American interests in China down the entire length of the Yangtze, at times convoying U.S. and foreign vessels on the river, evacuating American citizens during periods of disturbance and in general giving credible presence to U.S. consulates and residences in various Chinese cities. In the period of great unrest in central China in the 1920s, Palos was especially busy patrolling the upper Yangtze against bands of warlord soldiers and outlaws. The warship engaged in continuous patrol operations between Ichang and Chungking throughout 1923, supplying armed guards to merchant ships, and protecting Americans at Chungking while that city was under siege by a warlord army.