By special acts of Congress, the Medal of Honor was bestowed on the Unknown Soldiers of the United States who rest at the Tomb of the Unknown Soldier in Arlington National Cemetery, and — as a gesture of shared sacrifice after World War I — on the Unknown Soldiers of Belgium, France, Great Britain, Italy and Romania.
The Vietnam Unknown was identified through DNA testing in 1998 as Air Force First Lieutenant Michael Blassie and returned to his family; the crypt now stands empty as a tribute to all missing service members.
Official Medal of Honor citation
By virtue of an act of Congress approved 4 March 1921, the Medal of Honor, emblem of the highest ideals and virtues, is bestowed in the name of Congress of the United States upon the unknown, unidentified British soldier and French soldier buried, respectively, in Westminster Abbey and Arc de Triomphe.
Whereas Great Britain and France, two of the Allies of the United States in the World War, have done honor to the unknown dead of their armies by placing with fitting ceremony the body of an unidentified soldier, respectively in Westminster Abbey and in the Arc de Triomphe; and
Whereas animated by the same spirit of comradeship in which we of the American Forces fought alongside these allies, we desire to add whatever we can to the imperishable glory won by the deeds of our Allies and commemorated in part by this tribute to their unknown dead; Now therefore,
Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That the President of the United States of America be, and he hereby is, authorized to bestow with appropriate ceremonies, military and civil, the Congressional Medal of Honor upon unknown, unidentified British soldier buried in Westminster Abbey, London, England, and upon the unknown, unidentified French soldier buried in the Arc de Triomphe, Paris, France (A.G. 220.523) (War Department General Orders, No. 52, 1 December 1922, Sec. II).
Citation text: U.S. Government, public domain.