The spotter is also there to search for possible targets in a wider area than the sniper’s narrow angle of sight through the scope, and when the sniper doesn’t need assistance in target finding, the spotter is supposed to watch both their backs and surroundings. This to avoir getting captured (or worse) because you were so focused on what’s going on at a thousand yards, you didn’t hear footsteps right behind you.
Right idea, wrong details.
The stadimeter (the name of that device) relied on knowing not the length of a ship beforehand, but its height at a given, easily identified point (generally, topmast or first smokestack height).
The stadimeter then divided the periscope view into two halves. You centered the periscope on the target’s chosen reference point, then manipulated the scope so that the waterline on the right half of the picture was level with the reference point on the left half, giving you the angle.
Then the targetting computer instantly trig’d the range, using the angle you just input and the height you’d input before (height/tan angle = distance).
Note that the length of the ship, if known, *could *be used to determine distance (and speed) of the target using similar trig calculations as well, but not as easily or rapidly as with the stadimeter, and in that case the skipper also had to determine (read : guess) the angle on the bow of the target by sight alone. Some skippers were amazing at this, but trust this subsimmer, it’s really not an easy skill to master :).
I’m not splitting semantic dead hairs now, just trying to understand the basic physics:
When I think of the literal meaning of a “vapor trail,” I think of steam, say, like the stuff that comes out of a teapot when it comes to boil and it’s really hot, just like a bullet would be at the end of its flight (hence my wild-assed attempt to relate the word in sniping to the P. G. singularity.
Is “heat shimmer ruffling the already-present heat shimmer” correct? If so, why is that called “vapor…”?
And that’s not particularly vapor either - at least not if you can see it. If you can see it, that means you’ve got liquid water droplets (although they are probably surrounded by a substantial amount of gaseous water, i.e. steam).
It’s sort of correct, and I guess you could call it vapor, since air is a vapor. But the shimmer is due to schlieren, in which local variations in air density cause refractive bending of optical paths. The heat shimmer is caused by variations in air density due to uneven heating; the shimmer coming off of the bullet is caused by variations in air density created by the shock wave emanating from the bullet. See also here.
One of the duties of the spotter in a battlefield situation is to also share the moral resposiblity for someone getting shot and killed. This in the longer term results in a sniper who is much more effective and less likely to suffer from battlefiels stress.
There may be some psychological differences between manning a machine gun and firing a sniper rifle. A sniper takes some time getting to know a specific target in a what that the machine gunner does not. With a modern scope the sniper also gets to see up close personal details on his target that the machine gunner does not. On the other hand, some of the most successful Finnish and Russian snipers of the 2nd World War didn’t seem to need spotters to carry some of the moral responsibility of killing.
This is probably most commonly done nowadays with laser rangefinders, but you know all those little lines that typically appear near the crosshairs on a scope reticle? These are degree marks, typically mils, which allow you to fairly accurately estimate the range to the target. For instance, if you estimate the average man to be 6 feet tall and you see one standing up straight and his apparent height within the scope reticle is X mils, you could use some basic trigonometry to calculate your range to him fairly accurately.
If anything, it’s a matter of peer pressure - a sniper operating alone may hesitate to shoot, but one with a squadmate lying next to him would be ashamed not to.