periscope

In my case, it probably would be “Down periscope”—after accidentally ramming some Greenpeace research vessel.

There was no shelling at the moment, but rifle bullets kept flopping into the parapet especially when the periscope was moved.

Every hundred yards or so I had a close peep at the ground in front through de Lisle's periscope.

The periscope is the one part of the submarine scout equipment that is open to vision from the surface.

Curiously the others crowded about the object glass of the periscope.

And just then the Weathercock shouted something which sounded very much like "Periscope!"