1) Coastal artillery
Found on
https://www.crosswordclues.com/clue/plotting-board
A plotting board was a mechanical device used by the U.S. Coast Artillery to track the observed course of a target (typically a moving ship), project its future position, and derive the uncorrected data on azimuth (or direction) and range needed to direct the fire of the guns of a battery to hit that target. Plotting boards of this sort were first...
Found on
http://en.wikipedia.org/wiki/Plotting_board
No exact match found.
