periscope
noun [ C ] uk/ˈper.ɪ.skəʊp/ us/ˈper.ɪ.skoʊp/
潜望镜
a long, vertical tube containing a set of mirrors that gives you a view of what is above you when you look through the bottom of the tube
Periscopes are used in submarines to allow you to look above the surface of the water. 潜水艇上装有潜望镜，通过它可以观察水面以上的情况。