Plotting Board M17, Felsenthal Instruments Company Model FAO-52

Description:

Soldiers in the U.S. Army infantry plotted the relative position of guns, base points, and targets using instrumentslike this one. A plastic rotating disc pivoted on a flat plastic base. The base is square on one side and semicircular on the other. Printed in red on the base, directly under the disc, is a rectangular grid of lines. Numbers on the grid (moving out from the center of the disc) range from 0 to 19, representing hundreds of yards. Each small grid square thus represents 50 yards on a side (or, if one uses a scale to the left of the first one, 100 yards on a side).

To plot directions, one uses a scale on the edge of the disc which is divided evenly in mils from 0 to 6400, with every 10 units marked and every 100 units labeled (the labels go from 0 to 63). A vernier along the top edge of the base allow for further subdivision. Having measured the distance and azimuth of both a gun and a target, one can find the distance between them (the range required) and the direction in which the gun should be aimed.

A mark on the upper right of the base reads: BOARD, PLOTTING (/) M17. Also on the top edge of the base is a scale of centimeters divided to millimeters. Along the right edge of the base is a scale of inches divided to tenths of an inch.

The instrument fits in a cloth case.

This example of the M17 was made by Felsenthal and had Felsenthal model number FAO-52. According to a tag received with the object, it dates from 1962.

Compare 1977.1141.13 (the M10 plotting board) and 1977.1141.14 (the M17). On the M17, the map scale readings at the bottom right are in meters, on the M10 these are in yards.

References:

Accession File.

U.S. Marine Corps, MCWP 3-15.1, Machine Guns and Machine Gun Gunnery, 1996, pp. E-1—E-7. This is a description of the M17 plotting board.