Another fabulous oddball was the dynamite gunboat USS Vesuvius, built by Cramps, launched in 1888 and commissioned in 1890. She represented a radical concept in weaponry; her only armament was a 3-barrel, pneumatic 15" gun which shot 550-lb dynamite shells up to 1.5 miles away (249.5-kg shells shot to distances up to 2.41 km, for our metrically-minded readers). The gun was built into the hull of the ship and could not be rotated; to aim it the entire ship had to be turned, making target practice a cumbersome operation. Range was adjusted by varying the pressure of compressed air used to propel the projectile. The dynamite gun was tested in the bombardment of forts at Santiago de Cuba during the Spanish-American War. However, Vesuvius' principal contribution to the American victory was unrelated to her experimental weaponry. Due to her good turn of speed, she was often used as a despatch boat during the war.

The pneumatic gun was dropped. There were difficulties with training the weapons, and the conventional gun foundries surely wanted to bury this potential competitor. TNT was incorporated into naval warheads, but they continued to be fired from rifled breech-loading cannon using an explosive charge. The acceptance of this system brought with it tacit acceptance of the consequence: poor visibility in battle conditions due to volumes of thick, heavy gunsmoke mingled with funnel smoke in a new form of manmade naval smog. Battle accounts of the time always mention the density of the smoke with surprise. But in that time before radar, poor visibility had a tangible effect on gunnery and thus on battle outcomes. And as ever in naval history, wind, weather, and fickle fortune all made their influence felt.

Like many a dockyard oddity, Vesuvius spent much of her time laid up between commissions. In 1905 the dynamite gun was removed and she was converted to a torpedo research vessel, fitted with torpedo tubes of various sizes. She remained in commission through WWI, was finally stricken in 1920 and sold for scrap in 1922.