The subaltern took up a periscope and got the thread-line on the target-you find the range without instruments and by your own intuitions.
"Leaves from a Field Note-Book"
J. H. Morgan
The order that "liners" should not be torpedoed under any circumstances was regarded simply as a piece of red tape, and not applicable to war conditions, as the submarine was not in a position to distinguish through its periscope between "liners" and other craft.
"My Three Years in America"
Johann Heinrich Andreas Hermann Albrecht Graf von Bernstorff
It was absolutely impossible for the submarine captains to ascertain with certainty through the periscope whether an enemy merchant ship was armed or not.
"My Three Years in America"
Johann Heinrich Andreas Hermann Albrecht Graf von Bernstorff