What is 75 calibre?

75 calibre typically refers to the bore diameter of a gun or artillery piece. It means that the diameter of the gun barrel is 75 times the size of the ammunition or shell it was designed to fire. So for example, a 75 calibre gun would have a bore diameter of 75mm if designed to fire a 1-inch (25mm) shell. The term "calibre" comes from the Latin word "calibre", meaning "diameter of a cylinder or gun barrel". In general, guns with a larger calibre can fire larger, more powerful shells and projectiles.