On June 5, 1950, the communist force adopted the leapfrog tactic under the cover of shore batteries on adjacent islands and islets close by, succeeding in taking Dong'ao (东澳) Island, Greater Ten-thousand Mountain (Da Wanshan, 大万山) Island, and Lesser Ten-thousand Mountain (Xiao Wanshan, 小万山) Island, forcing the nationalist to withdrew to Outer Linding (Wailinding, 外伶仃) Island, Burden Pole (Dangan, 担杆) Island and other outlying islands. On the night of June 26, 1950, the communists had secretly set up the long-range shore batteries on Tri-gate (Sanmen, 三门) Island under the cover of darkness, and the communist gunboats were also deployed accordingly.