Modern mass production firearms are breech-loading (though mortars are generally muzzle-loaded). Early firearms were almost entirely muzzle-loading. The main advantage of breech-loading is a reduction in reloading time—it is much quicker to load the projectile and charge into the breech than to force them down a long tube, especially when the tube has spiral ridges from rifling. In field artillery, breech loading allows the crew to reload the weapon without exposing themselves to enemy fire or repositioning the piece (as was required for muzzle-loaded weapons) and allows turrets and emplacements to be smaller (since breech loaded weapons do not need to be retracted for loading).