During a war in which the United States is a neutral nation, it shall be unlawful to send out of the United States any vessel built, armed, or equipped as a vessel of war, or converted from a private vessel into a vessel of war, with any intent or under any agreement or contract that such vessel will be delivered to a belligerent nation, or to an agent, officer, or citizen of such nation, or with reasonable cause to believe that the said vessel will be employed in the service of any such belligerent nation after its departure from the jurisdiction of the United States.