Anti-tank guns are guns designed to destroy armored vehicles from defensive positions. In order to penetrate vehicle armor, they fire smaller caliber shells from longer-barreled guns to achieve higher muzzle velocity than field artillery weapons, many of which are howitzers. The higher velocity, flatter trajectory ballistics provide terminal kinetic energy to penetrate the moving/static target's armor at a given range and contact's angle. Any field artillery cannon with barrel length 15 to 25 times longer than its caliber was able also to fire anti-tank ammunition, such as the Soviet A-19.