Anti-tank vehicles made their first major appearance in World War II. Typically, these vehicles mounted a high-velocity cannon on a relatively light tracked chassis. As a consequence, they sacrificed armor for speed and manuverability. They met with only limited success.
Modern vehicles typically employ a guided missle, often wire-guided. Some modern force structures do not employ anti-tank vehicles anymore. For example, the U.S. Army has main battle tanks (the M1?) and the "anti-tank vehicles". Other vehicles (such as the M113? armored personnel carrier) may mount anti-tank missles for defense, but that is not their primary role.