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is it possible to have one unit with multiple weapons inside it?
for example, a horde of thirty warriors, the front rank armed with additional hand weapons for the extra attacks, but the second and third ranks armed with halberds and shields for the extra strength?
i havn't found anything against it in the rules, but if it is legal, would it work?
It's not legal, all the models have to use the same weapon at the same time.
That being said, you can carry halberds and shields or even more if you want - but you have to pick one for the entire unit to use in close combat until the engagement ends. Shield/halberd is a good combo for the armor save vs. ranged and the str. bonus against melee. Just be sure to let your opponent know which weapon you are using before you roll for combat [and you don't get the shield armor bonus with halberds in CC].
Sona si Latine loqueris.
One of the 8th changes made it so units with special weapons have to use their special weapons - they cannot choose to use HW and Shield, even at the beginning of a round.
So, if you bring halberds/great weapons, etc, they must be used, but you can bring a shield for the extra protection while marching across the field. However, there are some special exceptions (like Armed to da teef for Orcs, I think) that allow the player to choose which weapon they use before the first round of combat, but not many.