A license is not required with respect to the manufacture or use of any invention assigned or required to be assigned without restrictions or qualifications to the United States when such manufacture or use is by or for the Government for governmental purposes. A license or sublicense may be required, however, for such manufacture or use in the case of Class B patents or patent rights when the terms under which the Secretary of the Interior acquires interests therein necessitate the issuance of a license or sublicense in such circumstances.