"Luzon" and "Mindanao" were the largest, "Oahu" and "Panay" next in size, and "Guam" and "Tutuila" the smallest. China in the first fifty years of the twentieth century, was in low-grade chaos. Warlords, revolutions, natural disasters, civil war and invasions contributed. Yangtze boats were involved in the Nanking Incident in 1927 when the Communists and Nationalists broke into open war. Chiang Kai-shek's massacre of the Communists in Shanghai in 1927 furthered the unrest, US 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 USS "Palos" 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 Yichang and Chongqing throughout 1923, supplying armed guards to merchant ships, and protecting Americans at Chungking while that city was under siege by a warlord army. Standard Oil ran the tankers "Mei Ping", "Mei An", and "Mei Hsia" on the river, in addition to many motor barges, launches, tugboats and other tankers. These three tankers, the largest in the oil company's fleet, operated on the river until 1937 when they were bombed by the Japanese in the USS Panay incident. In the second half of 1934 Settle arrived in China, tasked with sailing USS Palos (PG-16) 1,300 miles (2,100 km) up the Yangtze River from Wusong to Chongqing. Palos, a gunboat stationed around Shanghai since 1914, had recently been refitted and over time became twice as heavy against her original displacement (340 vs. 180 tons), making her hardly capable of the upstream journey. In 1929 alone, of 67 Yangtze steamers three were totally destroyed by the rapids with 47 casualties; a thousand junk sailors perished every year. Of course, the Royal Navy had three generations of gunboats on the Yangtze River spanning fifty years.