Wis. Stat. § 321.43: Exemption from civil authority.

During the time the national guard or state defense force is performing military duty under orders issued by the governor or adjutant general, all of its members, while going to, remaining at, or returning from a place of duty are exempt from arrest or service of any process issued by a civilian court. In any civil or criminal prosecution against any member arising out of the member’s performing military duty, it shall be a defense that the member was acting in good faith or under a lawful military order. The order shall be considered lawful unless shown to be unlawful.