Not many computers about from 1910s to 1930s! :) (apart from mechanical ones used for e.g. artillery) My guess is basic lines being drawn on a physical map usi

Not many computers about from 1910s to 1930s! :) (apart from mechanical ones used for e.g. artillery) My guess is basic lines being drawn on a physical map using observations spaced over time, and then humans trying to spot the pattern. I think these sort of sound mirrors are fairly directional, so with a bunch pointing in various slightly different directions you might be able to find the "sweet spot" and at least get an idea of where the enemy is, even if it is not precise. From my own personal half-forgotten memories of seeing these as a kid in the 90s, they always seemed to be aligned with the coast, e.g. facing directly out to sea, not at an angle. This I guess would get you a lot of subtlety different directions to take a sounding from. Very interesting.