Very-long-range shooting pretty-much requires a precision laser rangefinder.
Very-long-range shooting pretty-much requires a precision laser rangefinder.
= = =
Maybe they had pre-surveyed various locations.
Or a friendly artilleryman or mortar forward observer who can handle trig and plane geometry, or a tank with an optical rangefinder better than 6-8 feet between the lenses, good out to about 3000 meters.
In cities, distances can sometimes be reasonably accurately estimated from the height of still-standing multistory buildings, if there are any, and at least one enterprising highway patrol cop rifleman I know works by reading highway passing zone stripes. The distance between railway/road telephone/telegraph poles has been used the same way, but in these days of cell phones that's going away. The fence posts are still up, though.
And of course there's always the old Finnish trick of counting the paces as you fall back from a previously held position. You then find a good firing spot where you can nicely observe your old location, and wait first for the other people to occupy it, then for your delayed-action demolition charge to go off. Once the survivors come staggering out, an easy shot or two, maybe three, at the surprised and stunned survivors can be taken with minimal risk, and you can then fall back and repeat as needed. Or, if available, call in for artillery/mortar support once the medics begin working.