Whistler-Hearn Plotting Board, Model 1904 - Casemate Museum, Fort Monroe - Hampton, VA
From its inception, the Coast Artillery had to address a very difficult problem: how to bring accurate and timely fire against a fast-moving target. The position of enemy ships had to be determined through triangulation sightings taken from two or more observation posts. When the target was located, its bearing and speed also had to be determined. This information was used in the battery plotting room, where soldiers used slide rules, charts and plotting boards to make mathematical calculations to provide data for the gun crew. Three pieces of information were critical to solving the problem: target location, direction, and speed. This knowledge allowed soldiers to determine where the enemy was going, allowing the fire direction center to create the data that would place a high explosive shell on the target. All of these calculations had to be made quickly and accurately. The Coast Artillery Corps utilized several different types of plotting boards between 1901 and 1950. The Whistler-Hearn board was an early 20th century model designated for use with a horizontal base of lengths from 900 to 7,000 yards. This extremely rare board came from a battery commander's station at Fort Story, Virginia, where it was used for a battery of 155-mm guns placed along the beach. The large photo in the background shows the fire detection center of a Coast Artillery battery in the Philippines in 1941.