Tampion

A tampion or tompion (in the Royal Navy)[1] is a wooden plug, or a metal, canvas, rubber, or plastic cover, for the muzzle of a gun, howitzer, or mortar.

To combat rust when ships were not in action the barrels were sealed, both with a tampion and plugs in the touch hole.

A quantity of olive oil and a round shot were left inside in the barrel; With the gun laid horizontally the shot would roll up and down the barrel as the ship caught each wave, effectively lubricating the gun simply through the motion of the ship.

Plastic tampions are normally designed to be expelled by the build-up of pressure in the barrel as the first shell is fired.

Nowadays, even warships that typically would not carry heavy guns, such as submarines, have their own badges in the shape of a tampion.