A Field Marshal is the highest rank in the British Army , and some other armies , such as the German Army . The equivalent rank in the U.S. Army is the Five-star General . The French rank of field marshal should not be confused with the rank of Marshal of France , which was the highest rank of the Ancien RÃ gime and is in effect the highest French rank today ( although in theory it is not an actual rank but a `` state dignity '' ) .