Ranging artillery

An L81 Mortar or an SPH-2 is not aimed down a barrel at something you can see. You are throwing a shell over terrain at a spot someone else is looking at, which means three numbers have to be right at once: the bearing you traverse to, the elevation you dial, and the height difference between where the gun sits and where the shell lands.

Get the bearing wrong and the shell lands the right distance away in the wrong direction. Get the elevation wrong and it lands on the right line, long or short. Both errors look identical from the gun — nothing lands — which is why ranging is a procedure rather than a guess, and why a spotter who can report which way a round missed is worth more than one who just says "miss".

The sight is graduated in mils, not degrees. A mil is a thousandth of a radian: at 1,000 m, one mil moves the point of impact by about one metre. That is the whole reason the unit exists — it turns an angle into a distance you can picture, and it makes small corrections expressible as whole numbers rather than fractions of a degree.

The dial does not run from zero to vertical. The L81 Mortar works between 120 and 950 mil, and the SPH-2 between 0 and 1400. Those limits are the practical edge of each gun: below the minimum the tube cannot depress far enough, above the maximum it cannot elevate.

Higher mil does not simply mean further. Past about 45 degrees of barrel elevation, winding the gun up makes the shell land closer, not further away, because you are trading distance for height. That is the single most counter-intuitive thing about indirect fire, and it is why the same target usually has two answers.

For almost any target inside the envelope there are two elevations that put a shell on it. The low arc throws it flat and fast; the high arc lobs it up and drops it in steeply. They land in the same place and are not interchangeable:

• The low arc is quicker. Less time in the air means less time for the target to walk out of the beaten zone. If the target is a vehicle, or infantry who have no idea you exist, the low arc is usually the one.
• The high arc clears things. A ridge between you and the target eats a flat shell. A steep arc goes over it and comes down almost vertically, which also matters for a target sitting in a courtyard or behind a building.
• The high arc is easier to correct. A steeply falling shell converts a small elevation change into a small distance change. On a flat arc the same correction moves the impact much further.

The artillery calculator lists both, with flight time for each. Flight time is not trivia: on the high arc a shell can be in the air long enough for anything mobile to have left, and it is the number that decides whether you fire at a moving target or at where it is going.

A firing solution assumes the target sits at the same height as the gun. When it does not, the shell arrives early or late. A target above you is effectively further away: the shell has to still be climbing, or less far into its fall, when it gets there. A target below you is nearer, and a solution computed for flat ground sails over it.

This is why the calculator asks for a height for your position and treats targets as level with the ground: give it the gun's height and it corrects the arc for the difference. The correction is not small. Over a kilometre, a few dozen metres of height difference moves the impact point by enough to miss a building.

In practice: if you are shooting from a ridge down into a valley, expect your first round to go long, and if you are shooting from a valley floor at something on high ground, expect it short. Correct in that direction before you correct in any other.

1. Get a grid, not a description. "Near the church" is not a firing solution. A coordinate is. Plot the target and your gun on the calculator and read off the bearing and the range.
2. Lay the bearing first. Bearing errors are the ones that waste the most ammunition, because a round that lands 200 m off-axis tells your spotter almost nothing about your elevation.
3. Fire one round, not three. A salvo makes it impossible to tell which round was which. One round, observed, is worth a magazine fired blind.
4. Correct along the line of fire. Ask the spotter for the miss in metres, long or short, relative to your line — not theirs. "Left" from a spotter standing at ninety degrees to your gun means nothing to you.
5. Re-plot rather than guess the new mil. Move the target marker to where the round actually landed, read the new solution, and apply the difference. This is more reliable than estimating mils per metre in your head, because that ratio changes with range and with which arc you are on.
6. Fire for effect once it lands. The L81 Mortar reloads in 6.5 s and the SPH-2 in 27 s, so know before you start which of those two rhythms you are working to.

They are not the same tool. The mortar is buildable, reloads in 6.5 s, and covers short range — useful for a position you are holding, where targets appear a few hundred metres out and the value is in volume. The SPH-2 is a vehicle, reloads in 27 s, and reaches out to kilometres, which makes it a deliberate weapon: you site it, you range it, and each round has to be worth the wait.

The reload gap is the deciding factor more often than range is. Four mortar rounds land in the time one SPH-2 shell does. Against anything that moves, the gun that can correct four times beats the gun that gets one attempt.