Angular Mil - Use

Use

The angular mil is commonly used by military organizations. Its relationship to the trigonometric radian gives rise to the handy property of subtension - that "One mil approximately subtends one metre at a distance of one thousand metres". More formally the small angle approximation for skinny triangles shows that the angle in radians approximates to the sine of the angle. More usefully an angular mil or mil subtends about 1 m at a range of 1,000 m.

Angle can be used for both calculating size or range. Where the range is known the angle will give the size, where the size is known then the range is given.

When out in the field angle can be measured by using calibrated optics or quite approximately ones fingers & hands. With an outstretched arm one finger is approximately 30 mils wide, a fist 150 mils and a spread hand 300 mils.

Angle can be used for calculating range. For objects of known size the range is the size divided by the angle. Land Rovers are about 3 to 4 m long, "smaller tank" or APC/MICV at ~6 m (e.g. T-34 or BMP) and ~10 m for a "big tank." From the front a Land Rover is about 1.5 m, most tanks around 3 - 3.5 m. So a SWB Land Rover from the side are one finger wide at ~100 m. A modern tank would have to be at a bit over 300 m.

Artillery spotters typically use their calibrated binoculars to walk fire onto a target. Here they know the approximate range to the target and so can read off the angle (+ quick calculation) to give the left/right corrections in metres.

Note: Do not confuse the angular mil with the MOA (minute of angle). 1 mil ≈ 3.43774677078493 MOA