instrument used in submarines to keep watch on enemies________.
Periscope is used in submarines to keep watch on enemies. Kindly refer to the following link:
https://www.meritnation.com/ask-answer/question/what-is-a-periscope-and-waht-is-its-use/light/3572949
https://www.meritnation.com/ask-answer/question/what-is-a-periscope-and-waht-is-its-use/light/3572949