So when you buy attachments it says that you attachment them after you deploy your models. So does this mean that you can switch who it is attached to between rounds? Also can a model have more than 1 attachment?

One deployment card can not have more than one attachment.

One deployment card can not have more than one attachment.

Pg 5, Rules Reference Guide, Attachment: When the Imperial player deploys figures to the map, he may take ONE OR MORE "Attachment" cards and place them on the figures' correspinding Deployment card.

I don't see any restriction to one attachment?

And to answer the OP, if the group that has the attachment(s) gets defeated, the attachment(s) become available again. You can then add them to any other figures that you deploy. You can't move them to a group already in play though.

in skirmish a deployment card can only have one attachment

in campaign they can have as many as you like

Ah, you're right! I don't play Skirmish often, I didn't realize Skirmish had attachments. I see now that got introduced in some of the expansions?