(a)
Requirement that officers and employees travel on American ships
Any officer or employee of the United States traveling on official business overseas or to or from any of the possessions of the United States shall travel and transport his personal effects on ships registered under the laws of the United States where such ships are available unless the necessity of his mission requires the use of a ship under a foreign flag. The Administrator of General Services shall prescribe regulations under which agencies shall not pay for or reimburse officers or employees for travel or shipping expenses incurred on a foreign ship in the absence of satisfactory proof of the necessity therefor.
(c)
Motor vehicle owned by Government personnel
Notwithstanding any other provision of law, privately owned American shipping services may be utilized for the transportation of motor vehicles owned by Government personnel whenever transportation of such vehicles at Government expense is otherwise authorized by law.