Question Bolt WMDs

[Aolain]

I am playing Bolt 5.3 as NATO. My opponent has hit me with chemical weapons. Naturally I wish to give him a dose of righteous vengeance. When I select either a missile or arty unit flagged for WMD, and select nuclear or chem weapons in the drop down menu it tells me no valid units with chemical or nuclear weapons have been selected. Any ideas what’s up?