Visitors view the guided-missile destroyer Guiyang of the Chinese People's Liberation Army (PLA) Navy during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Guo Xulei)

Crew members and visitors take a selfie on Russian Navy tug ship Nikolai Chiker during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Yu Lan)

Visitors are seen on Royal Thai Navy frigate HTMS Bangpakong during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Guo Xulei)

A Thai frogman jumps into water during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Wang Yuguo)

Visitors stand on guided-missile destroyer Guiyang of the Chinese People's Liberation Army (PLA) Navy during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Wang Yuguo)

Visitors purchase souvenirs on Royal Thai Navy frigate HTMS Bangpakong during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Wang Yuguo)

Visitors view Royal Thai Navy frigate HTMS Bangpakong during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Guo Xulei)

Visitors pose for a photo in front of hospital ship Peace Ark of the Chinese People's Liberation Army (PLA) Navy during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Ma Jing)

Visitors view the guided-missile destroyer Guiyang of the Chinese People's Liberation Army (PLA) Navy during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Qian Yi)

Visitors take photos during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Luo Xiaoguang)

Visitors are seen during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Ma Jing)

A crew member introduces torpedo installations to visitors on the guided-missile destroyer Guiyang of the Chinese People's Liberation Army (PLA) Navy during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Yu Lan)

Visitors prepare to board guided-missile destroyer Guiyang of the Chinese People's Liberation Army (PLA) Navy during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Ma Jing)

Visitors view hospital ship Peace Ark of the Chinese People's Liberation Army (PLA) Navy during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Guo Xulei)

Visitors take photos of the guided-missile destroyer Guiyang of the Chinese People's Liberation Army (PLA) Navy during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Wang Siwei)

Visitors view the landing vessel Jinggangshan of the Chinese People's Liberation Army (PLA) Navy during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Guo Xulei)

An interpreter introduces the guided-missile destroyer Guiyang of the Chinese People's Liberation Army (PLA) Navy to visitors during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Luo Xiaoguang)

Visitors prepare to board on the guided-missile destroyer Guiyang of the Chinese People's Liberation Army (PLA) Navy during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Luo Xiaoguang)

Visitors are seen during a warship open day event in Qingdao, east China's Shandong Province, April 24, 2019. A warship open day event was held on Wednesday in Qingdao, as part the multinational naval events marking the 70th founding anniversary of PLA Navy. (Xinhua/Guo Xulei)