just an idea that came suddenly and had no relations to anything particular =)
could be implemented just to add some peculiarities to the new mod in case our dear developers are eager to process a considerable hack.
A trench in its current representation is a 1- or 2-unit slit in the ground. Troops cannot move inside it. During the war trenches are most often combined to create a long system of covered communications (see for example Soviet preparations for battle of Kursk when about 5k km of trenches were dug).
The in-game features could be such that units can transport themselves from one point of a long trench to another one. During this march they cannot attack/be attacked from the ground level. To attack, enemy units should leave the ground level and enter the trench (in this case they cannot attack/be attacked from the ground level). Skirmishes inside trenches are possible - with adjusted fire modifiers TBD.
Such trench systems are an obstacle for light vehicles (like tank traps would do), but are crushed in places by heavy vehicles.
To avoid extra animation work troops transportation inside trench systems could be made invisible or just represented as "standard trench length1 is occupied with a squad" - "length1 is free; length2 is is occupied with a squad" - "length2 is free" ....
