@Vance:
Instead of making them a hit soak, how about:
Infantry entrenchment.
One infantry per territory per turn may be entrenched at a cost of $2. No more than 3 entrenched infantry may occupy a single territory. Trenches are represented by a trench roundel placed under the infantry unit and are immobile. An infantry unit to be entrenched must have been in the territory at the start of the turn. If entrenched infantry are later moved or killed, the trenches remain unless they are destroyed by the enemy.
Entrenched infantry are immune to attack by enemy infantry, mechanized infantry, artillery, or shore bombardment. Only armor and air units can kill entrenched infantry. Trenches may be destroyed by artillery or shore bombardment.
Example: you attack 2 entrenched infantry with 1 infantry, 1 artillery, 1 fighter, and a cruiser bombards. On the first dice roll you hit with the infantry and a cruiser. The infantry hit doesn’t count but the cruiser shot de-trenches 1 infantry. The defender doesn’t hit anything.
On the second dice roll you get hits for the infantry and fighter. The enemy also gets a hit. The untrenched infantry is killed by the infantry hit and the fighter hit kills the entrenched infantry. One trench remains unscathed. You decide to lose the artillery and occupy the territory with 1 entrenched infantry.
So if you are amphibiously assaulting an island with entrenched infantry you will always want shore bombardment (to weaken enemy defenses), air support (to kill the enemy), armor (to kill the enemy), and infantry (hit soak to protect your armor OR to occupy a usable defensive position). Bringing artillery might be a bad idea because trenches would soak hits from artillery and you might want to preserve those defenses for yourself.
I like this, but I think you should be able to place entrechments equal to the territories IPC value. Islands have a max of 3, No ipc territories have a max of 1.