Slitherine

I don’t think it’s intended that every aircraft attack from whatever class completely robs the entrenchment, isn’t it?
That means that even dogfighters that hardly do damage to ground targets can eliminate an entrenchment of 10, while most artillery guns never scratch it.

Hm they should not do that and a quick test didn't cause an entrenchment drop either. Are you sure that's what happened?

For example when you start the scenario "Battle of Bataan" on Japanese side you see the entrenched line of recruits on the right. When I buy a single Zero and start the mission, it will completely reduce the shovel/entrenchment value from 7 to 0 when you attack a single time. It is the same with other types of planes in other missions.

I've added two saves before and after the attack of a Zero.