Tactics is a knowledge skill. It is often a specialization. Tactics: capital ships, Tactics: fleets, Tactics: starfighters, Tactics: ground assault, and Tactics: squads are all specializations that have been identified by WEG. There are more. Two bonuses are given for a successful tactics roll which are Anticipate Enemy, and Decieve Enemy
A Moderate tactics roll is needed to anticipate the enemy. If the roll is successful, a commander's troops/ship is allowed to perform ONE action that is resolved BEFORE their enemy's action(s). Already declared actions may NOT be changed. All cmage results (or other results) are resolved before proceeding with the rest of the round. This bonus is often due to the commander "evaluating" the tactical situation and anticipating what the enemy will do. This bonus relies mainly on the commander's evaluation of the situation rather than any actual troop manuevers s/he has commanded thus, a Command roll need not follow this tactics roll.
A Difficult tactics roll is needed to "deceive the enemy". Success on this roll allows a commander to REDECLARE all his/her actions (and those of all his/her troops) after hearing what his/her opponent(s) have declared. This rule is good way of getting the enemy to do something you want (by baiting them with your first declaration) and then using that action against them (by redeclaring). This rule is very powerful when the declaration order is based on PER or DEX. I think it would also be advantageous with initiative-based declaration. Deceiving the Enemy is often due to "feints", "probes" and the like that are designed to reveal how the enemy will act. This Tactics roll is often followed by a Command roll to be successful since troops must be coordinated to perform the action which will deceive the enemy.
NOTE: The character must indicate which tactical bonus he/she is trying for BEFORE the tactics roll.
If both the sides in a conflict are making tactics rolls, use Opposed rolls to resolve who gets a bonus. The roll must still be over the difficulty number. Only one side gets any one tactical bonus in a round.
In many cases the Tactis skill will replace the Command skill, or be used in conjunciton with it. This is because to deceive an enemy, sometimes you must get your troops to perform a coordinated action (i.e. a "probe" or "feint"). GM's may wish to have two rolls made: one for the commander's tactical knowledge, and one to command the troops to conduct the action. This equates to a Tactics roll followed by a Command roll.