In campaign games such as the Samurai Swords Campaign, armies can make opposed naval landings. Such invasions are more than the standard DBA four-element littoral deployment rule can cover.
The following rule governs how an army makes such an invasion, and how it can attempt to withdraw by sea.
In an amphibious invasion game, terrain is set up normally, except that a Waterway is mandatory, and must be placed on the invader's base edge of the table. The invader deploys within 600 paces of the Waterway, and does not set up a camp. Also, the invader cannot deploy any mounted elements, artillery, or war wagons.
The defender sets up normally.
If the invading army withdraws or is defeated (see Post-Battle Recovery), it must evacuate by water. If the invading army wins, after the battle it lands its camp and any other elements that were not allowed to deploy during the invasion.
In addition to invasions, a defending army may be attacked in a position where there is no overland route of retreat. This could include the former amphibious invader being counterattacked during the next campaign turn.
In such cases, the army is defending a beachhead, and terrain is set up with a Waterway on the defender's base edge of the table. The defender deploys all of it elements (including a camp and those elements not allowed an amphibious invader) within 600 paces of the Waterway.
The attacker sets up normally.
If an army defending a beachhead withdraws or is defeated (see Post-Battle Recovery), it must evacuate by water.
To evacuate by water, an element must begin the bound touching the Waterway. Each element evacuated by water costs one PIP. Note that, while withdrawing elements are alllowed a zero-PIP move toward the base edge of the table, actually leaving the table by water does cost one PIP per element.
Since animals and vehicles cannot easily be evacuated by water (they generally have to be abandoned or destroyed), only the riders and crews actually escape. To simulate this
Allowing mounted elements a half-chance to evacuate is simpler than requiring the player to pay for replacing their mounts.