Philippine troops march as a Philippine Air Force C-130 transport plane carrying Philippine Defense Secretary Delfin Lorenzana, Armed Forces Chief Gen. Eduardo Ano and other officials, sits on the tarmac at the Philippine-claimed Thitu Island off the disputed Spratlys chain of islands in the South China Sea Friday, April 21, 2017 in western Philippines. Their visit Friday was aimed to assert the country's claim to the heartland of a disputed area where China is believed to have added missiles on man-made islands. The South China Sea issue is expected to be discussed in the 20th ASEAN Summit of Leaders next week. Seen in the background above the horizon, center, is the Chinese man-made island of Subi Reef. (AP Photo/Bullit Marquez), APTOPIX