Any unit of artillery, cavalry or infantry existing in this Commonwealth on the passage of the act of Congress of May 8, 1792, which by the laws, customs or usages of this Commonwealth has been in continuous existence since the passage of said act shall be allowed to retain its ancient privileges, subject, nevertheless, to all duties required by this title. Said organizations may be a part of the Pennsylvania National Guard and entitled to all the privileges thereof and shall conform in all respects, except as to cornets, to the organization, discipline and training of the National Guard in time of war. For the purpose of training and when on active duty in the service of the United States, they may be assigned to higher units, as the Governor may direct, and shall be subject to the orders of officers under whom they shall be serving.