Depends on how many civilians are armed. If you had a WHOLE BUNCH of civilians armed and shooting up the place, you would send in the national guard with fully militarized weapons, live ammunition, heavy weapons like .50 cal machine guns, night vision equipment, heavily armored humvees with bullet proof glass and impose a curfew. The troops would also assist police. Those troops would be used to enforce a curfew.
Anybody who is out past curfew runs the risk of being shot by those troops. An extreme measure like that might be the only way to restore order then. It's hard to distinguish who is armed given that weapons are easily concealed. So, a curfew with troops given the legal authority and wide latitude to exercise the use of lethal force given to enforce that curfew would probably be necessary though I would use that as the absolute last resort.
In Iraq, imposing curfews was used to combat the insurgency there with one exception: our forces had much wider latitude to legally use lethal force to enforce a curfew given you had a much bigger and more dangerous insurgency where they would have some Iraqis go out at night to dig holes and plant IEDs to kill our troops with and others could be carrying concealed weapons. The Iraqis were warned ahead of time about the curfew. The curfew was pretty effective in that case.
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