Anti-tank guns (towed or self-propelled) are cannons or guns designed to destroy enemy armored vehicles normally from defensive positions. In order to penetrate vehicle armor they fire anti-tank ammunition from longer-barreled guns to achieve higher muzzle velocity than field artillery weapons, e.g. 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.