The ship was not accepted by the Union Navy so her builder began seeking buyers elsewhere; Otto von Bismarck expressed some interest, and the thought of Prussia armed with such a vessel prompted France to purchase her and commission her in 1867 with the name Rochambeau. She was initially placed in reserve, but was mobilized in 1870 to participate in the Franco-Prussian War. The ship saw no action and was decommissioned after the end of the war. Rochambeau was stricken from the Navy Directory in 1872 and scrapped in 1874.
Design, description and construction
On 11 April 1862,
US Navy Department. Webb signed a contract on 3 July with the Navy's Bureau of Yards and Docks for a ship that had an overall length of 350 feet (106.7 m), a beam of at least 68 feet (20.7 m) and a draft of no more than 20 feet 6 inches (6.2 m). His ship was required to make 15 knots (28 km/h; 17 mph) in still water and she was to be armed with four 15-inch (381 mm) Dahlgren guns in two gun turrets, each protected by 11 inches (279 mm) of armor, and eight 11-inch Dahlgren guns in a casemate. The ship was to be completed in 15 months at a cost of $1,250,000.[2]
Now named Dunderberg by Webb, the contract was amended on 27 August to specify her armor scheme. Above the main
double bottom and her engine and boiler rooms were to be completely enclosed by watertight bulkheads. She was also to be provided with two masts and the appropriate rigging.[3]
The ship was powered by two
auxiliary boilers to provide steam for the steam engines that powered her pumps, ventilation fans and rotated the gun turrets. These engines, with their bore and stroke of 36 inches (914 mm), were larger than the main engines of the Passaic-classmonitors. All of the boilers exhausted through a retractable funnel.[4] The ship normally carried 540 long tons (550 t) of coal, but could hold a maximum of 1,000 long tons (1,000 t). She had a light brigantine rig[6] that had a sail area of 11,170 square feet (1,038 m2).[7]
Her
longest wooden ship ever built.[5]Dunderberg's hull was protected from biofouling by two external layers of zinc and copper. The ship was fitted with two rudders, the primary one in the usual location aft of the propeller, but she also had an auxiliary rudder placed in the deadwood above and ahead of the propeller.[11]
Many other changes were made to Dunderberg while she was under construction and significantly contributed to her delays in completion. The most important of these was the eventual elimination of her turrets
Illustration from Harper's Weekly showing Dunderberg under construction in late 1863. Note the prominent ram at the ship's bow.
Dunderberg was built with a plough-shaped 44-foot (13.4 m), ram bow of which the forward 12 feet (3.7 m) were sheathed in cast iron.[10] Her full armament was not installed before she was sold, but gunnery trials were conducted in February 1867 with two 15-inch and four 11-inch guns. With a gun port height of 50 inches (1,270 mm), the 15-inch guns could elevate +8.5° and depress to −5°; equivalent figures for the 11-inch guns were +5° and −7°. The 15-inch guns could traverse 30° forward of the beam and 28° aft and the 11-inch Dahlgrens could bear 28° to both sides. The only significant problem encountered during the trials was that the gun deck was made of soft pine and did not withstand the force of recoil well.[15]
Other problems that delayed the ship's completion were shortages of material, labor and money. Prices for
boiler plate and copper roughly doubled. Wages of even inexperienced workers increased between 50 and 100 percent. The New York City draft riots in July 1863 and several machinist's strikes
further slowed progress on Dunderberg. Webb failed to account for these problems when negotiating the ship's contract and he repeatedly tried to charge the Navy for alterations as well as use cheaper materials to reduce his costs. He also attempted to have his contract amended by act of Congress, but he was unsuccessful. The Navy agreed to pay for some of the changes made and it also reduced the reserve amount held back in case the
ship did not meet her specifications in 1865.[16]
By about 1864, both sides regarded the ship as a
private bill passed by Congress in March 1867 that allowed him title to the ship once he repaid all monies advanced to him.[17]
French service
Illustrated London News
After Prussia expressed an interest in the ship, the
Emperor of France, Napoleon III, bought her in April for 2.5 million dollars over the objections of his own navy, which preferred a home-built ship.[18] The exact date of purchase is unknown, but Welles noted in his diary on 7 May that Webb had told him of the sale. On 27 June, Webb refunded the money that had been paid to him and also purchased those items furnished by the government. A little over a week later, he attempted to sail to France, but had to return to port the following day due to engine problems. These were not resolved until 19 July when he, and his entire family, set sail. Dunderberg arrived at Cherbourg on 3 August and the French Navy took possession three days later.[19]
The ship was commissioned and renamed Rochambeau, in honor of the
breech-loading. The 15-caliber 270-millimeter (10.6 in) guns fired a 216-kilogram (476 lb) shell while the 17-caliber 240-millimeter (9.4 in) guns fired one that weighed 144 kilograms (317 lb). The 270 mm guns were mounted in the corners of the casemate and could pivot between a broadside gun port and one on the corner. Eight of the 240 mm guns were mounted on the broadside and the remaining two were positioned in the bow and stern gun ports. The remaining four gunports, those on the corners closest to the broadside, were plated over.[21]
The French carefully measured the ship during her 1868 overhaul. At the waterline Rochambeau was 107.4 meters (352 ft 4 in) long and had a beam of 22.15 meters (72 ft 8 in). She had a mean draft of 6.5 meters (21 ft 4 in), a
metric horsepower (2,900 kW), but they produced a maximum of 4,657 metric horsepower (3,425 kW) and gave a speed just over 15 knots during her machinery trials in June 1868 after the completion of her overhaul. At normal load she carried 540 tonnes (530 long tons) of coal and 735 tonnes (723 long tons) at deep load. In service the ship proved to burn a lot of coal, full bunkers and 30 tonnes (30 long tons) stored on deck provided her a range of only 2,200 kilometres (1,200 nmi) at a speed of 8 knots (15 km/h; 9.2 mph). They reduced her sail area to 954.42 square meters (10,273.3 sq ft).[22]
They measured the ship's armor thickness throughout. The casemate was completely protected by 120-millimeter (4.7 in) plates. The hull armor extended to a depth of 2.5 meters (8.2 ft) below the waterline and its upper
head sea. She had a very quick roll which caused problems when trying to work the guns in heavy weather as even moderate seas could prevent their use altogether since the gun ports were only about 1.4 meters (4 ft 7 in) above the waterline. Under sail alone in a good breeze, the ship could not maintain her course, could not be steered and would turn until wind and wave were on her beam.[23]
Rochambeau completed her refit on 18 May 1868 and was briefly under the command of
Minister of Marine) before being decommissioned on 1 August and placed in reserve. She was refitted from August to December and had her forward hull armor plates replaced by a one-piece cast iron ram. Still in reserve in 1869, Rochambeau was modified with an additional 240 mm pivot gun mounted over the forward end of the casemate and the pine planking underneath the guns in the casemate was replaced by oak.[24]
The ship was recommissioned with a crew of 600 men in mid-July 1870, just before the beginning of the Franco-Prussian War. She departed Cherbourg on 25 August to join the fleet in Danish waters and reached
Jade Estuary on 26 September for Prussian ships, but they found nothing.[25]
Upon her return, Rochambeau was decommissioned again and her crew was ordered to help defend Paris. The ship was stricken from the Navy List (Liste de la Flotte) on 15 April 1872 and was scrapped sometime in 1874.[26]
Notes
^The rationale for the thicker aft deck armor is not given, but it appears to be intended to protect the machinery spaces that were vulnerable to a plunging shell fired from the rear.[3]
^The exact date is not known, but references in Webb's letters place it between 23 September and 3 October.[8]
Roberts, Stephen S. (1993). "The French Coast Defense Ship Rochambeau". Warship International. XXX (4). Toledo, Ohio: International Naval Records Organization: 333–345.
Roberts, William (1993). "Thunder Mountain: The Ironclad Ram Dunderberg". Warship International. XXX (4). Toledo, Ohio: International Naval Research Organization: 363–400.
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