The US Navy manuals refer to "Column 19" and the "Change in height of impact for variation of 100 yards in sight bar." While this sounds like a complex parameter, it is simply the tangent of the projectiles impact angle with respect to horizontal, which is called the angle of fall and is listed in the range table shown in Figure 2. This figure shows how to find the curvature for a range of 19,800 yards, which is 84 feet. At the intersection of the row and column, we find a curvature of 84 ft.įigure 4: Table of Curvatures for Different Horizontal Ranges. We go to the row that corresponds to 19,000 yards and find the column that corresponds to 800 yards. To illustrate how to read this table, consider the range of 19,800 yards. This table duplicates the results shown in this reference. We can use Equation 1 to compute a curvature versus range table (Figure 4). These parameters are illustrated in Figure 5. R is the radius of the Earth (3963.2 miles).δ deviation from horizontal, which is called curvature in gunnery.I have written about how to compute the curvature of the Earth over a given distance in another post using Equation 1, which relates the deviation from horizontal to the distance from the measurement origin. My goal in this post is to show how we can correct the LOS distance to provide the required horizontal distance, which can then be used to read the gun elevation from the table in Figure 2.Īll calculations are performed in Excel – my workbook is here. The LOS distance must be corrected to an effective horizontal distance that can be looked up in the range table. The rangefinders on a battleship determined a Line-Of-Sight (LOS) distance, but that distance is not the same as the horizontal distance listed in the table of Figure 2. Figure 3: Example Where Target is Lower Thanįigure 3 shows that firing at a target that is at sea level also involves a difference in heights.
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