Technical Report—U.S. Navy Gunnery and the Plymouth

The sloop-of-war Plymouth in 1857 became the first U.S. Navy vessel dedicated to improving fleet gunnery and developing improved ordnance. Her assignment marked a turning point in the U.S. Navy’s modernization.

The Plymouth's designation was the result of rising professionalism in the Navy, the support of Secretary of the Navy James Dobbin, and especially Commander John Dahlgren’s scientific ordnance experiments, which included the development of new heavy guns.

Then-Lieutenant Dahlgren had been assigned to the Washington Navy Yard in 1847 and charged with drawing up range tables for Navy guns. He later designed a boat howitzer and new, heavy, shell guns for the Navy. His work was the real beginning of the use of scientific techniques in the design and employment of U.S. naval ordnance.

Dahlgren was an effective advocate of the new shell guns. Introduced first in France by Colonel Henri Paixhans, these guns were designed primarily to fire explosive shells, as opposed to the solid shot used by the older guns. The success of the nine-inch shell gun designed by Dahlgren led to its inclusion in the batteries of the six new first-class, propeller- driven steam frigates of the Merrimack class. Authorized in 1854, these were the finest and most powerful of their type in the world. All were launched by the end of 1856, the same year that Dahlgren published his most important book on naval gunnery—Shells and Shell Guns.

The Merrimack class of frigates was to be armed entirely with shell guns. This was an innovation, since England and France considered shell guns as auxiliaries in batteries composed primarily of 32-pounders (bore diameter 6.4 inches) The new frigates were armed with nine- inch guns in broadsides on the gun deck and heavy pivot guns at bow and stern of the spar deck; but the pivot guns were only ten-inch rather than the 11-inch guns Dahlgren had wanted. Also, eight-inch guns were substituted for the six pivoting eleven-inch guns that Dahlgren had proposed between the fore and main masts on the spar deck. Five of the frigates were armed in this fashion, but the sixth—the Niagara—was armed quite differently. The builder, George Steers, took only Dahlgren’s spar-deck plan; he refused to sacrifice speed to the heavier weight that Dahlgren’s proposal entailed. The Niagara thus emerged as a large sloop-of-wat armed with nine-inch guns, making her unique in the U.S. Navy at the time.

The success of the Merrimack and her class lessened Navy opposition to shell guns and helped convince Secretary of the Navy Dobbin in August 1856 to assign the sloop-of-war Plymouth to Dahlgren and the Naval Ordnance Department as an experimental ordnance vessel. In early March 1857, Congress authorized $49,000 “to arm and man the ordnance ship ‘Plymouth,' with a view to the improvement of ordnance and gunnery practice.”² 

The Americans were at last following British practice. As Dobbin noted in his annual report at the end of 1856, the British had since 1830 maintained a gunnery Practice ship, HMS Excellent, “where officers and men are trained to the use of cannon as thoroughly and as accurately as the soldier is drilled in the army.” Americans had hitherto relied on practice at ^sea, an inadequate procedure. The Plymouth was to serve as a “Gunnery Practice-Ship” carrying an experimental battery in the hope that seamen serving on her would become proficient in the “management of heavy ordnance in storm and in calm.”³ Dahlgren saw the Plymouth in just that light, as an experimental gun platform from which to test his ordnance and develop more effective procedures for the handling and firing of his guns.

On 9 October 1856, the Plymouth anchored at the Washington Navy Yard. The next day, Dahlgren noted in his journal that he had requested for her one 11- inch and four nine-inch guns, carriages, three 24- and three 12-pounder howitzers (bore diameters 5.82 and 4.62 inches, respectively), and 100 new rifled muskets—of his design—along with 50 revolvers. The Navy approved all but the last, authorizing only muskets of the old pattern.

The rifled muskets he designed were later authorized. Two divisions of seamen on board the Plymouth used them, while the other two divisions were armed with the older weapons. In subsequent trials afloat and ashore, the Dahlgren musket proved its worth, being noted for “simplicity of use, and capacity to endure the roughest usage.” The musket was subsequently adopted by the U.S. Navy, and an 1864 report of the Chief of Ordnance noted that there were then in service 10,000 muzzle-loading, rifled, .69-inch muskets “known as the Plymouth musket.”⁴

The Plymouth was a first-class sloop rated at 20 guns. Her displacement has been given variously as 974 and 989 tons. Her length was 147 feet, 6 inches, beam was 38 feet, 1 inch, and she drew 16 feet, 4 inches. She carried a crew of 210 officers and men and was built in 1843 at a cost of $170,586.⁵ At the beginning of 1850, the Plymouth was armed with four eight-inch shell guns and 18 32-pounders. By 1853 this had changed to a total of six shell guns.⁶ The Plymouth was in the Mediterranean in 1844 and 1846, and had taken part in Commodore Matthew Calbraith Perry’s opening of Japan in 1853 and 1854.

After her arrival at Washington, modifications were approved to allow her to carry the heavier Dahlgren guns, particularly the nine-inch version on a pivot mount. These changes were made, and pursuant to Dobbin’s orders received on 23 June 1857, she left Washington the next day. She was gone 134 days, 34 of which were spent in ports of call.

The cruise took the Plymouth to the Azores and Lisbon, Portugal; Amsterdam in the Netherlands; Southampton, England; and Bermuda before her return home. Lack of time precluded visits to ports in Belgium and France.⁷ The Plymouth exhibited excellent sailing qualities during the cruise despite the burden of the nine-inch pivot gun, which—with its carriage—weighed 24,500 pounds. In addition to the pivot gun, her armament during the cruise consisted of the four nine-inch shell guns on the new Marsilly carriages in broadsides, plus two 24- pounder and one 12-pounder howitzers.⁸

As Dahlgren saw it, the reason for the cruise was “to ascertain the calibres and weights of ordnance best-fitted to give the greatest power to the broadside. ...” He was also determined to prove the efficacy of his 11-inch pivot gun, especially because other powers had, in his words, “been prompt to follow the example set by the United States and to improve on it.”⁹ Larger frigates than the Merrimack were being constructed in Europe; they were faster and mounted larger guns.

When firing the nine-inch gun in ideal sea conditions, the crews were able to achieve an average of one shot every 40 seconds. This was nearly as rapid a rate as that achievable with a long 32-pounder or the eight-inch shell gun of 63 cwt (cwt denoted a “hundred weight”—actually 112 pounds). It also compared very favorably with HMS Excellent's record of an average of 43 seconds for each of 11 rounds from a 32-pounder and 46 seconds for the same number from an eight-inch gun.¹⁰ When the sea got rougher, a well- drilled nine-inch gun crew could still fire at a good rate: one round every 65 seconds when rolling 5° and one round every 95 seconds when rolling 18°.

The biggest advantage, however, was the ease of firing the 11-inch pivot gun in bad weather. In calm seas it could be fired no faster than one round a minute; but a sea state that caused the crew of the nine-inch broadside gun to slow down, was less of a problem for the 11-inch gun crews. Once, against a target about 900 yards away, the crew of the 11-inch gun fired 13 shells—to starboard and to port— while the two adjoining nine-inch guns together were able to fire a combined total of only 17 shells.

On one occasion, the 11-inch gun was required to pivot to stay on target as the ship was tacked. This occurred in light airs, but a considerable swell caused the ship to roll 7-9° and pitch 3°. Dahlgren concluded that the 11-inch gun was in every way as manageable as the 64- pounders (8-inch guns) “which have been so long, and are now, used on board our steamers.” During the cruise, 121 11-inch and 230 nine-inch shells were fired.

In Europe Dahlgren had the opportunity to inspect the cannon foundry at Liège, Belgium, and also visited Woolwich Arsenal, England, where he was introduced to the Select Committee on Ordnance, in addition to going on board HMS Excellent. His visit to Woolwich convinced him that the Americans were ahead of the British in “all the main points” of ordnance. The United States lagged only in the “extent [and] excellence” of machinery; although this, he noted, could be purchased. Dahlgren believed that the chief shortcoming of the British system was “the union of Land and Naval Ordnance.” As he put it, “how can landsmen know the troubles of ships, or knowing them, how shall they know the remedy?”

Dahlgren also inspected the new British steam frigate Mersey, rated at 40 guns. He was on board the screw frigate Diadem, a 32-gun vessel, and one of the new larger class of British steam frigates— designed to rate with the Merrimack class—when she made her first trial. He also saw another type of screw frigate, Galatea, then building at Woolwich. In his diary Dahlgren noted with satisfaction that during a visit to Portsmouth he had been complimented on his book. Shells and Shell Guns, and was told that some of his doctrines had been put to practical test on board the Excellent and “had been entirely confirmed.”¹¹

Immediately on her departure from Portsmouth, the Plymouth ran into extremely rough weather. Although a trial for both ship and crew, the week-long storm provided a good test of the security of the new, heavy Dahlgren guns in bad weather. Critics had maintained that it would be impossible to secure the guns in a severe storm; Dahlgren was pleased to report that, on board the Plymouth, they remained secure with only ordinary lashings.¹²

The vessel returned to the United States from her five-month cruise on 11 November 1857, and Dahlgren submitted a report to Secretary of the Navy Isaac Toucey, who included it his annual report to Congress on 8 December 1857. It was subsequently printed in full in the New York Daily Tribune and, slightly condensed, in The Times of London. In his report Dahlgren noted that the most important function of an ordnance ship such as the Plymouth was the training of the men who would handle guns aboard ships at sea: “Science may achieve the utmost in perfecting the cannon and their appointments, but if the crews are deficient in drill and practice, better men with inferior means may bear away the palm.”

It was therefore of the utmost importance to find seamen who were fit both “physically and intellectually” for instruction as gunners and gun captains- Dahlgren recommended inducements such as higher rank and pay to those who qualified.

Toucey noted that the result of the Plymouth's cruise was “to dispel all remaining doubt whether the heavy cannon which she carried would be manageable, Md not only to justify the previous adoption of such ordnance in the steam frigates recently built, but also to render it expedient to extend the plan of armament.” The ease in handling of the 11-inch gun had also been proved.¹³ In his annual report Toucey wrote: “In the Dahlgren gun we have found what we Want, and it is believed there is no gun in any service that surpasses it. . . ,”¹⁴The Merrimack-class frigates now at last had their armament modified to conform to Dahlgren’s proposals. Spar-deck armament was changed to nine-inch guns in broadside and a pivot-mounted 11-inch gun at bow and stem.¹⁵ Put simply, the 1857 cruise of the Plymouth demonstrated the feasibility of arming U.S. Navy ships with heavy guns.

The vessel spent the winter of 1857-58 at the Washington Navy Yard, where Congressmen and government officials ^visited her. At the end of 1858 she was sent to Annapolis, Maryland, to be used as a school ship. In late April 1861, along with other Union vessels, she was scuttled at the Gosport (Norfolk, Virginia) Navy Yard, to prevent the Confederates from seizing her.

This did not deter the Confederates; they raised the Merrimack and commissioned her as the Confederate States Ship Virginia. They also raised the Plymouth and planned to sail her up the James River to assist in the defense of Richmond. Before this could be done, however, the Federals recaptured the yard and the Confederates scuttled her again—for the final time—in May 1862.