Okla. Stat. tit. 47, § 47-157.3: Actions to be brought against insurer

Any person or persons suffering damages from the claimed

negligent acts of any of such departments, their officers, servants,

employees, or agents, arising from the operation of the vehicles,

motorized machinery, or equipment so insured is hereby authorized to

maintain an action to collect damages against the insurer. The

insurer may not plead as a defense in any action involving insurance

purchased by the authority of this act the governmental immunity of

either the State of Oklahoma, the State Highway Department, the

State Department of Agriculture, or the State Department of Public

Welfare, or any other subdivision of state government.