Ambushing the enemy is not possible in CIV 4 and I believe that adding such capability can add new strategy and a lot of fun to CIV 5. Here is how it could work: “Ambush” will apply to both defense and attack. Players will have to choose between setting a defensive position (25% max defense bonus) or setting an “Ambush” (50% max defense bonus – 10% per turn). Ambushing will only be possible in Forests, Jungles, and Hills. Players cannot set an ambush if there is a Fort in that tile. Units will continue to enjoy the tile natural defensive bonus (on top of the ambush bonus). Units that are in max ambush position (50%) would not be seen by other units other than scouts and spies. Units that are in a partial ambush position (less than 50%) may or may not be seen by normal units (base on a formula). Spies and scouts will not always see units in ambush position. We will need a special formula to calculate that probability. It will be the hardest to detect one unit in ambush position. The more units in ambush position – the easier (more probable) it will be for the spies and scouts to detect them. Not all units can set an ambush position (e.g. tanks). If units that are in “Ambush” position are visible to the enemy then the “Ambush” defense bonus will be converted to the normal defense bonus (25% defense instead of 50%). We can then have special promotion related to ambushing. Spies and scouts can have “ambush unit detection” promotion to improve the chances for them to detect ambush units. Normal units can have “ambush strength” promotion as well as “counter ambush strength”. If the enemy moves an entire stack into a tile that is occupied by units in ambush position (when the ambushing units were not seen by the enemy) then the combat will involve all the units in the stack as well as all the units in the ambush tile. Players that were ambushed will be given a chance to retreat after 3 or 4 combat rounds and they will suffer additional damage if they choose to retreat. “Ambush” will apply also to units that attack. Units in ambush position can attack enemy units that are one tile away from them with up to 50% extra attack (for having the element of surprise). However, if they were seen by the enemy then the attacking units will not enjoy any “Ambush” bonus. The defending units will still enjoy their tile defensive bonus. The defending units will be selected randomly for ambush attacks (instead of the best counter unit). This means that attacking ambush units will have better chances to defeat the enemy. The same rule applies to ambush units in a defensive position – the ambushed unit will be selected randomly. When a unit gets ambushed then only one unit at a time will be revealed. For example, if the enemy moved 3 units to a tile that was ambushed by 5 units. His 3 units will die by 3 ambushing units (that will be revealed). However, the other 2 units that were also in ambush position will not be revealed. This is the general idea and I am sure it can be improved and get tweaked some more. This “Ambush” capability will allow defenders to set ambush position against attackers. Attackers can also surprise their enemies by setting ambush positions in enemy territory (in key defensive points) and then go on a massive attack or pillaging. The ambush units will then ambush reinforcements from other cities or units that try to intercept pillaging units. I believe that this setup will add plenty of strategy to the game that includes guerilla warfare. Here is an example for ambush tactics that can be used. A player can set an ambush longbow units in a tile and then place there knight unit (without setting it in ambush). The enemy sees only the knight and sends a pikemen to intercepts it. The pikemen is then ambushed by the longbow (for being the best counter unit) that defeats the pikemen. The enemy then sees its pikemen being defeated by the ambushing longbows. However, he doesn’t know if there are more ambush units in that tile. This will require players to calculate every step when they moving their army units around. It will be probably a good idea to add an option to disable “ambushing” if you think that complicates the game play too much. Players can then decide if they want to play with ambush units or not. Another option could be to disable “ambushing” only for the AI (allowing players to have all the fun ambushing the AI left and right).