Paixhans developed a delaying mechanism that, 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. Henri-Joseph Paixhans first demonstrated this 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 had a fuze that ignited automatically when the gun was fired; they lodged in the wooden hull of the target, and exploded a moment later: