To share some historical information, the U.S. Army Infantry was and is the oldest of all the combat Arms Branches, not only in the U.S. Army but going back through history.  As most history buffs will recall, the Ancient Greeks were the first to create the Infantry by introducing a tactic that was called “The Greek Phalanx” (i.e., flexible battle formation).  Until the Romans improved on it, this tactic was dominant for centuries.  Needless to say, both the Infantry and the U.S. Army have come a long way since the Greek & Roman Days. Today’s modern Infantry can move by land, by sea and by air.