I stumbled into this 1920s American training document on building fortifications with the lessons of World War I in mind. The full piece has detailed guides on everything from “the kind of thing you build when you have only a few hours” to “the kind of thing you build when you have a few years”. Both fighting positions and gargantuan medical/residential/command underground dugouts (or “cave shelters” as the document calls them) are there.
There are a couple things I found interesting in particular. The first is that antipersonnel mines, despite becoming a hallmark of later fortifications, are only mentioned very briefly and dismissively. According to it, they take too much effort to emplace for something that’s going to be knocked aside/detonated by the big artillery preparation already. (Antitank mines, including ones rigged to be sensitive, are treated somewhat more favorably.)
The second is that what became known as an overpressure system (ie, higher pressure in the area than out of it, pushing clean air out instead of poisoned air in) is talked about as a counter to poison gas for large bunkers. I didn’t know it was talked about that early, and thought it was a Cold War invention. So that was interesting.
The third is that while machine guns were present, very few of the later infantry support weapons were. Besides indirect mortars, the only thing talked about for forward emplacement is the 37mm infantry support gun. So this was a very interesting time capsule, and some of its TTPs (techniques, tactics, and procedures) are still relevant. After all, artillery hasn’t exactly gotten less lethal since the 1910s.