The board of county commissioners of any county having a population of more than two hundred fifty thousand (250,000) is hereby authorized and empowered to levy an annual tax on all the taxable tangible property in such county for the purpose of providing funds to be used for civil defense purposes and to pay a portion of the principal and interest on bonds issued under the authority of Kan. Stat. Ann. § 12-1774, and amendments thereto, by cities located in the county.