periscope

US /ˈper.ɪ.skoʊp/
UK /ˈper.ɪ.skoʊp/
1.

kính tiềm vọng

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.