The Trenches tile provides non-mechanical ground units with protection against attacks. If a unit is attacked by gunfire while it is entrenched, the Trenches tile provides 3 miss chances, absorbing up to three shots. Note that being entrenched does not offer any protection during indiscriminate damage steps such as those caused by bombardments or Gas. If a unit moves out of a Trenches tile, it is no longer entrenched and therefore the Trenches tile does not offer any protection during an attack of opportunity. If a unit bypasses an entrenched unit, then the Trenches tile does not offer any protection to the bypassing unit, whereas the entrenched unit is completely safe. The Trenches tile itself is indestructible.
Non-mechanical ground units that move onto an unoccupied Trenches tile must stop moving to become entrenched.