I'm currently reading E.B. Sledge's autobiography "With the Old Breed." It is thus far an absolutely outstanding read told from the perspective of a front-line infantryman.
Though my version of the novel has various anecdotes and references, I'm confused by a lot of the terms related to the sighting/target acquisition/target engagement by mortar teams, of which E.B. Sledge was a part. I've been searching YouTube and other resources and have come up dry.
What I'm wondering is, how did mortar teams in WW2 - the Pacific, particularly - "register" their mortars and then deliver accurate fire? I've read about stakes that were placed in the dark of night to mark distances. How did they use these stakes to place accurate rounds on targets many meters further from those stakes?
I'm not a historian but I spent over a decade as a mortar specialist. The stakes that you are curious about are not necessarily for distance. Almost every model of mortar designed after WW1 has a sight which rotates horizontally, 360 degrees. On American mortars the amount of rotation is measured in mils, with 6400 to make a full circle. So 0/360 degrees would be 0/6400 mils, 90 degrees 1600 mils, 180 is 3200, and so on. The sight rotates independently of the rest of the weapon, and 3200 is when it's aligned with the barrel. So if you have visual on a target and want to fire directly, the sight needs to be set at 3200. The thing about mortars, they are most useful as an indirect fire weapon. Stakes are placed ahead of the firing position in a certain direction. Could be due north of the gun, could be the most likely direction of fire, but the important part is that it's a known direction. Let's say we place a stake due south of the gun, then receive a call for fire against an enemy who is southeast (135 degrees) of our location. We can set the sight to 2400 (135) and then shift the whole gun so that the sight is on the stake. So now the sight is looking south but the barrel is southeast. About using stakes to mark distances, it's useful for mortars I'm sure, but more often used by machinegunners and snipers.