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Stockades can be captured by irregulars and cavalry. They do not revolt when left undefended. They auto-garrison with one militia or one line infantry, and the chance for doing so feels like it increases as the game progresses. Power 60+ stacks will regularly overwhelm autogarrisons, although this is less likely if composed of all rangers. A mtd vol combined with a ranger is likely to win in assault posture, as is a cav element combined with two or more rangers, as is a stack with four or more rangers (three rangers is less certain). Use assault if you have this kind of power; you will force the auto-garrison into a combat where you can overwhelm it in one turn.
If you are not strong enough to be sure of taking an auto-garrison in a single turn, enter the region under orange-green orders. The garrison will be inside the structure and possibly not even enter combat with you. If it does, light troops like cavalry and rangers disengage well so will take little damage. If the auto-garrison does not trigger, the stockade will be yours in either posture. If you cannot overwhelm a spawned auto-garrison, simply leave and come back later to try the auto-garrison roll again (gamey). Stockades are sometimes destroyed during combat.
In addition to their sizable amount of supply, stockades provide cover from harsh weather and speed hit and cohesion recovery rates compared to open territory. Large forces can move along stockade chains, staying supplied and in fighting condition despite harsh terrain and weather. A stockade’s defensive bonus is quite valuable in small scale battles, but becomes less important as the power of the forces involved increases. In the Plains, Texas and the Far West it is therefore usually ok to entrench small forces IN the structure rather than in front of it: it would take a pretty big stack to assault and destroy two entrenched elements with a fort bonus, and even if they did the defender would probably not lose any NM.
Destroying stockades you control takes one full turn and one day. Give the unit the destroy stockade order and end the turn. On the next turn the destroy order will still be selected. You can then move the unit anywhere you wish: it will still be in the region on Day 1 of the second turn to destroy the stockade. (You can also change your mind at this point and unclick the order, in which case the timer resets.) The message log at the beginning of the third turn will confirm that the stockade was destroyed due to heavy fighting and your unit will be wherever you told it to go.
Move troops along stockade chains. Stockades in forward positions bordering objectives or key cities provide supply, cover and recovery to attackers. Forward stockades are good positions for an Army to support an attacking Corps, although formations of this size will eat through an isolated stockade’s supplies quickly. Forces on the move that retreat in a battle tend to return to the region they came from; attacking from a stockade alomost gaurantees you will retreat safely back to the stockade if defeated. Stationary troops forced to retreat in battle are drawn to friendly structures, so will often retreat to adjacent stockades.
Create firebreaks around important positions by destroying nearby stockades that could be used against you. Interrupt chains of stockades to impede enemy movement along them. The Union will use stockades in the Indian Territories as bases to harass Texas and Arkansas if they are left intact. The CSA will seek to control or destroy the stockade chain between Fayetteville AR and Leavenworth KS whereas the Union will attempt to use it to support operations around Springfield/Fayetteville and as a path for reinforcements from the Leavenworth build point. The Union must defend Fts. Lyon and Garland in southern CO in order to safely move forces built in Denver south to New Mexico. The CSA will want to remove stockades surrounding El Paso and Mesilla to deny forward positions to the Union. If forced to withdraw from El Paso, the CSA will want to have pruned the stockades east of it into a one-wide chain that can be burnt during a fighting retreat to permanently isolate El Paso and prevent raiding into Texas. A large portion of the available supply in the Far West exists in stockades, and therefore is destroyable unlike in other theaters (favoring the CSA).
There is one time victory point bonus (+5 VP) for capturing stockades, and a victory point cost (-3 VP) to destroying stockades. This part of the game, while clearly a sideshow compared to the big battles East of Mississipi, has its importance in the Grand Campaigns. In Sibley's campaign stockades are a critical source of scarce VPs.
Build Outpost cards are plentiful and cheap. In addition to forward building and using them to establish movement and supply corridors, an outpost card can rescue a force stuck in bad weather and terrain. Stockades build in one turn and start with over 100 supply, but can only be built in regions without structures in which you have 50%+ military control. Artillery inside a coastal or river stockade prevents supply movement and attempts to fire on passing ships automatically just like prewar forts and redoubts. It will appear less successful at this than the bigger emplacements, but that is because Fort Batteries and Coastal Artillery have a sea detection of 4 where land artillery only have 3 so engage less often. If you were to somehow get one of these into a stockade, bombardments would occur normally.