§ 59-g. Exemption of property from state taxation. The property so conveyed and released to the United States shall be exempted from all taxes, assessments and other charges, which may be levied or imposed under the authority of this state; but the jurisdiction hereby ceded and the exemption from taxation hereby granted shall continue in respect to such property so long as the same shall remain the property of the United States and be used for purposes of public defense, and no longer.