I often use 3 or more gun units. Even when the weather is bad I have a balanced army which is still able to fight effectively and go on to win battles in the rain. My advice, like others here, always take at least a couple of gun units for their fear-factor and infinite ammo. If you do choose a fair number of guns, remember to take a couple of archer units so that if it does rain you still have some missile troops. The whole point of this game is that nothing should be left to operate on its own, all the units interact and support each other.

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"Put 'em in blue coats, put 'em in red coats, the bastards will run all the same!"