All contracts or agreements made by the Secretary of the Army or the Secretary of the Navy for the sale to the government of any American republic of any of the arms, ammunition, or implements of war, the sale of which is authorized by this subchapter, shall contain a clause by which the purchaser undertakes not to dispose of such arms, ammunition, or implements of war, or any plans, specifications, or information pertaining thereto, by gift, sale, or any mode of transfer in such manner that such arms, ammunition, implements of war, or plans, specifications, or information pertaining thereto, may become a part of the armament of any state other than an American republic.