To anticipate tactics would likely fall to Lore (military tactics) more precisely. But I would allow (with some penalty) K:nobility and sense motive. However engineering, geography, local and religion etc can used if they are factors at all coming battlefield (or survival if there is long distance travel involved through wilderness). So allow overall creative use of any knowledge based skills if they can be explained someway. Also perception can help (detect obvious tactical advantages in battlefield or openings foes can use). Local may be use especially if mercenaries are locals example. History if person knows the band's leader (accomplished leader with past wins and record).