Submarine's viewer (9)

I believe the answer is:

periscope

'submarine's viewer' is the definition.
(I've seen this before)

This is all the clue.

(Other definitions for periscope that I've seen before include "Sub's eye?" , "Submarine's eye?" , "Submarine's viewing tube" , "Viewing instrument in a submarine" , "Optical instrument" .)

I've seen this clue in The Times and The Star Tribune.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.