 Complete the following phrase:  The era of the wooden steam ship-of-the-line was brief, because of new, more powerful naval guns. In the 1820s and 1830s, warships began to mount increasingly heavy guns, replacing 18- and 24-pounder guns with 32-pounders on sailing ships-of-the-line and introducing 68-pounders on steamers. Then, the first shell guns firing explosive shells were introduced following their development by the French Général Henri-Joseph Paixhans, and by the 1840s were part of the standard armament for naval powers including the French Navy, Royal Navy, Imperial Russian Navy and United States Navy. It is often held that the power of explosive shells to smash wooden hulls, as demonstrated by the Russian destruction of an Ottoman squadron at the 