beachhead
noun [ C ] uk/ˈbiːtʃ.hed/ us/ˈbiːtʃ.hed/
（军队的）滩头阵地，滩头堡
an area of land near the sea or a river that an attacking army has taken control of and from where it can move forward into enemy country
The troops quickly established a beachhead and were preparing to advance. 部队很快建立了滩头阵地，准备继续向前推进。
Compare: bridgehead