A squad with the engineer specialization may do the following:
Dig Entrenchment: During the Action Phase, as an action, an engineer squad may be fatigued to create an entrenchment in its current hex. Simply take an entrenchment marker from the box and place it on the hex. Its player may then choose to have the engineer squad enter the entrenchment as part of this action.
A hex may not contain more than a total of three fortification markers (entrenchments and pillboxes in the TOI base game). If a hex already contains three such markers, no additional markers may be built there. Entrenchments may not be built in hexes containing stream, pond, or building terrain.