Why do gunners open their mouths when firing cannon?

Gunners often open their mouths to protect their eardrums while firing large guns. When the mouth is open the air waves set in motion by the discharge of the cannon enter the throat as well as the ears; consequently the sudden pressure against the outside of the drums is counteracted by an equal pressure against the inside. Opening the mouth while firing artillery is not so common among gunners as it formerly was. It is no longer practiced generally by members of the gun crews in the United [ 492 ] States Navy. Men working in the turrets are well protected from concussion, while those in the more exposed positions generally use ear stoppers or pledgets of cotton in their ears. In recent times several different devices have been developed to protect the ears of men when firing large guns. One of these is known as the “ear warden.” It is a device that keeps out loud noises without interfering with the ability to hear commands. Notwithstanding- these devices, many men, whether in combat or merely in artillery target practice, still open their mouths during the actual firing of large guns in order that the pressure on their eardrums may be equalized. Gunners also often stand on their toes to relieve the body as much as possible of the shock of the explosion. The ears are among the most intricate organs of the human body.