Technical Report—The ‘Dynamite Cruiser’

Night after night, the little ship stole close to shore off Santiago de Cuba to loose her whispering salvos. She had the sleek, graceful lines of a tycoon’s yacht, but packed the wallop of a heavy cruiser. The USS Vesuvius, unofficially known as the U.S. Navy’s “Dynamite Cruiser,” was bombarding the Spanish fortress at Socapa during the Spanish- American War, and making her mark on naval history.

The late 19th century was a time of rapid advancement in naval warfare. Sails gave way to steam, wooden hulls yielded to steel, and the development of naval armament was in full bloom. Capital ships were becoming larger and larger; by 1890, ships of 10,000 tons, bristling with many large-caliber guns had taken their place in the battle lines of the world’s leading navies.

The development of bigger ships with heavier armor naturally called for bigger guns and projectiles to combat them, but a serious problem with large-caliber naval shells emerged almost simultaneously. Higher muzzle velocities were required to give projectiles the momentum needed to penetrate the armor of capital ships, but dynamite, the bursting charge used for naval shells, was unstable; when subjected to the violent, rapidly expanding force created by standard black-powder propellants, shells tended to explode while still in the gun. The explosions were often catastrophic; either a more stable bursting charge or a less violent method of propelling projectiles was required.

The search for a feasible propellant led the U.S. Navy to experiment with a unique and innovative launching method— compressed air. The relatively gentle acceleration provided by compressed air seemed ideal, and the Navy built a ship to test the concept.

Christened the Vesuvius, she became the only compressed-air gun ship ever designed from the ground up and commissioned. She displaced only 930 tons, but carried the firepower of a cruiser. Laid down in Philadelphia’s Cramp Shipyard in September 1887 and launched in April 1888, she was 252 feet, 4 inches long; had a beam of 26 feet, 5 inches; drew 11 feet; and was powered by two four-cylinder triple-expansion steam reciprocating engines that gave her a record 21,4-knot speed.

Built only to test the compressed-air gun concept, she was never intended for open ocean operations. She rolled wildly (up to 40°, 12 times per minute), her high-speed engines quickly consumed her limited supply of coal, and her underpowered steering engines hindered her maneuverability.

The Vesuvius mounted three smoothbore, compressed-air guns that were 55 feet long, and had a diameter of 15 inches. The guns were rigidly mounted to the ship in a through-deck arrangement that placed the guns’ breeches near the keel, with their muzzles facing forward, approximately eight feet above the main deck. The gun barrels were flanged about ten feet from the lower end so that the breech sections could be lowered parallel to the keel for reloading ammunition that was contained in rotary drums. A charge of 1,000 pounds per square inch was used to fire the shells, and the ship could fire two rounds per minute.

After extensive experimentation, a 7-foot long, 10.5-inch diameter sub-caliber projectile carrying 200 pounds of blasting gelatin was chosen as the service projectile. These were fitted with a gas seal to center them in the bore, and spiral fins to stabilize them in flight, as the guns were not rifled. Initially, mechanical time fuzes were used, but they were replaced by impact fuzes, and fuzes activated by contact with salt water. The ship carried ten rounds per gun.

The concept of employing guns fixed in both train and elevation posed difficult fire- control problems; to be effective, the ship had to be pointed directly at the intended point of impact, and accurate range information was critical. Consider the difficulty of engaging other ships. The range problem was partially solved by devising a method to control the amount of firing air admitted to the guns. The firing air pressure remained constant, but the length of “firing” time was varied. It soon became apparent that while engaging other ships would prove difficult, the ship could possibly be used as a shore-bombardment platform.

Her air guns yielded several advantages not previously realized with powder guns:

► The guns were a great deal lighter, since they were made of half-inch-thick brass, instead of steel many inches thick.

► The ship did not have to carry potentially explosive black-powder propelling powder charges. (Many now believe that it was the spontaneous explosion of her powder charges that sent the USS Maine to her fate in Havana harbor in 1898.)

► The light guns permitted the ship to be much smaller than a contemporary cruiser, and gave her the shallow draft that permitted close approach to a hostile shore.

► Perhaps most interesting, the Vesuvius was stealthy; she could fire in almost complete silence, with no tell-tale muzzle flashes.

The Vesuvius’s gun system demonstrated two unexpected and beneficial traits during testing:

► When shooting at ships, her projectiles did not actually have to strike the target ship to be effective. If they struck the water as much as 50 yards short of the target, they would continue traveling underwater, on a path nearly parallel to the water’s surface. With proper fuzing, the shells could be detonated at or near the submerged portion of the target’s hull. This produced a much larger range window than was originally anticipated. As advantageous as this feature was, however, it did not provide reason enough to keep her employed in the antiship role. 

► The guns’ relatively high angle of elevation and short range (approximately 2,100 yards), gave the projectiles a highly parabolic flight path. As a result, the ship's pitching motion, even if significant, caused little range error. Prior to gyro- stabilization, pitching introduced large range errors in high-velocity, flat-trajectory naval guns that fired over the bow. The Vesuvius’s roll characteristics, however, proved a much more difficult problem; it was never solved.

After sea and gunnery trials, the ship began a routine career on the U.S. East Coast. While many in the Navy perceived her as a waste of money and plans for a sister ship were canceled, the public took an instant liking to her, and the popular press dubbed her the “Dynamite Cruiser.” The duties she performed were largely ceremonial, and the “Dynamite Cruiser” became a familiar sight as she visited ports along the eastern seaboard, showing the flag at various celebrations.

As relations with Spain worsened, though, the Vesuvius steamed to Key West, Florida, to join the American fleet. She departed Key West 28 May 1898 to participate in the blockade of Santiago de Cuba, and on 13 June began firing the missions that gave her a place in naval history. On eight different occasions, the ship closed the Cuban shore under the cover of darkness, firing three rounds per mission at the Spanish fortresses guarding Santiago de Cuba. Because her bombardments were without warning, she is reported to have caused “great anxiety” among the Spanish defenders, though she appears to have done little real damage to the fortresses.

Because of her limited ammunition supply, those missions were the only time she ever fired her guns in anger. Rear Admiral William T. Sampson complimented the ship. His official report of 22 June 1 898 remarked that “The Vesuvius has done almost nightly firing since she has been here. There is no doubt that shells of this character have a very important effect.”

The war’s end later that summer, coupled with the advent of smokeless powder—the long-sought gentler propellant- sounded the death knell for the popular Vesuvius.

She was decommissioned in Boston only three months after her missions against the Spanish strongholds. Recommissioned in 1904, she served as a torpedo test platform for three years. After another brief retirement, she was again recommissioned in 1910, and served as the station ship at Newport, Rhode Island, until 1921. She was decommissioned for the last time in October 1921, and scrapped in 1922. Her passing closed a unique chapter in U.S. naval history.