ABSTRACT
U-boats used periscopes to see above the https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781003239215/5b264eb7-ace5-478d-ba9b-a8ba902b78e1/content/fig4_29_103.jpg"/> water, but a periscope can also be used on land to peer over walls and around corners. You can build your own periscope with some easy-to-find materials.
