Volley gun
The Ribauldequin was a medieval version of the volley gun. It had its barrels set up in parallel. This early version was first employed during the Hundred Years' War by the army of Edward III of England, in 1339. Later on, the late Swiss army employed it.
Naval artillery
The first naval gun designed to fire explosive shells was the Paixhans gun, developed by the French general Henri-Joseph Paixhans in 1822–1823. He advocated using flat-trajectory shell guns against warships in 1822 in his "Nouvelle force maritime et artillerie", and developed a delaying mechanism which, for the first time, allowed shells to be fired safely in high-powered flat-trajectory guns. The effect of explosive shells lodging into wooden hulls and then detonating was potentially devastating. This was first demonstrated by Henri-Joseph Paixhans in trials against the two-decker "Pacificateur" in 1824, in which he successfully broke up the ship. Two prototype Paixhans guns had been cast in 1823 and 1824 for this test. Paixhans reported the results in "Experiences faites sur une arme nouvelle". The shells were equipped with a fuse which ignited automatically when the gun was fired. The shell would then lodge itself in the wooden hull of the target before exploding a moment later.