Perhaps the least known of the U.S. Navy’s Civil War–era ironclads was a highly innovative, technologically advanced, high-freeboard seagoing ship built solely to battle the Royal Navy. But she was never accepted into the U.S. Navy. Excitement over her construction lasted about one year, after which the supposed British threat evaporated and focus could be maintained on producing relatively inexpensive, quickly built riverine and light-draft monitors to combat the genuine (Confederate) threat. Through it all, the Dunderberg—Swedish for “thunder mountain”—suffered an extended gestation that resulted in her being obsolete at birth.
In early 1862, just a year into the Civil War, the United States feared two external threats: European—specifically, British—recognition of Confederate independence, and military intervention in support of that recognition. The Union blockade of Southern ports that shut off England’s supply of cotton for its textile industry, along with incidents such as the Trent Affair, brought the issues to the fore. War with England had to be avoided because, as Attorney General Edward Bates stated, “for the plain reason that now we are unable to meet it.”
At the time, the U.S. Navy was ill-prepared to fight the Royal Navy. Secretary of the Navy Gideon Welles believed that seagoing ironclads were necessary for protection; the Navy had but one, and she, the New Ironsides, was still under construction. The press, particularly The New York Times, strongly advocated large seagoing ironclads. New York shipbuilder William Henry Webb answered the call, sending the Navy Department a model of a “Steam Battery” in April 1862. The design was for a wooden-hull, casemate ironclad of 7,000 tons.
After discussions, primarily with Assistant Secretary of the Navy Gustavus V. Fox, Webb signed a contract on 3 July to build the warship for $1.25 million. The contract was extremely general with virtually no specifications. She was to be 350 feet long, with a beam of “at least” 68 feet, and a draft of no more than 20 feet, 6 inches. She was to carry two turrets atop her casemate, each armed with two XV-inch Dahlgren guns behind 11 inches of armor. Additional armament included eight XI-inch Dahlgrens within the casemate. She was to make 15 knots “in smooth water.” Completion was due within 15 months. Webb named her the Dunderberg.
On 27 August, new specifications arrived from the Navy Department detailing armor thickness and positioning and other points. The earliest plans show a “low mastless profile with a very pronounced ram built as an integral part of the hull.” The casemate, 155 feet long, had its faces angled at 35 degrees to the horizontal and was pierced by eight ports, three on each side and one each fore and aft. The turrets were 21 feet in diameter with an internal height of 8 feet. An armored pilothouse was to be built atop one of the turrets or the casemate. Engine design remained somewhat ambiguous, so Webb specified two horizontal direct-acting engines with 90-inch bores and 45-inch strokes.
From the start, the Dunderberg’s design was constantly changing, with many of the changes proposed by Webb. Because of this, her construction was tumultuous.
The first issue had arisen in August, just before the contract was amended. Webb found it almost impossible to contract for construction of the engines. With war-driven inflation significantly rising, “the prices named by the Engines builders for my Engines, especially the Boilers is [sic] truly fabulous,” he wrote. “I am in the worst fix of my business life.” He eventually settled on a contractor, John Roach, owner of the Etna Iron Works. But neither Roach nor his iron works had any experience building engines or boilers.
The hull also had issues, primarily related to obtaining the necessary wood. Webb was forced to used unseasoned timber, which would greatly shorten the life of the hull. The keel was not laid until 3 October. A year later, at the end of the 15-month construction deadline, only 40 percent of the hull and engineering work had been completed. That month, Webb changed the motive design to back-acting engines, with 100-inch diameter bores and the same stroke as the direct-acting type.
Roach was plagued with increased costs for all materials and even the unskilled labor he hired. Inferior iron delivered through mid-1863 proved unworkable, forcing additional delays in engine construction. Further, the New York City draft riots in July 1863 “materially interfered” with progress on the ship, as did the machinists’ strikes in late December. By October 1864, completion was forecast for “probably” the summer of 1865.
The ship’s 1864 configuration differed greatly from that of the year before. The turrets were eliminated from the design, and a basic two-mast sail rig was mounted. The turrets had proved too complex to construct affordably. In September 1864, Welles approved a new main battery and configuration for the ship. She would mount four XV-inch and a dozen XI-inch guns all within the casemate. This was extended 73 feet to a length of 228 feet. The angle of its faceplates was changed to 60 degrees to afford more internal space and allow for easier construction and protection of the gun ports. At that, the XV-inch guns were difficult to accommodate. The pilothouse also had to be fitted to the casemate. For an unknown reason, Webb designed it with an elliptical rather than, as all the monitors had, a circular cross section. His subcontractor refused to build it. A design based on that of the Miantonomoh class was chosen, built, and installed.
The change in the casemate forced the reworking of most of the ship’s internal compartments, most notably those of habitation. The officers’ quarters and wardroom were moved from the casemate to the berth deck, which had to be rearranged. It also forced the lengthening of the hull but decreased her beam, adding further delays.
The Dunderberg was virtually completed when the war ended in April 1865. The ship was launched with half her armor in place on 22 July. Construction continued slowly, with Webb in a precarious situation. He had no other constructions in progress; financially, she was literally keeping his shipyard afloat. The worst situation would be for the Navy to accept the ship, which it was obligated to do, at the contract price. Webb had already spent far more than that and was hoping to renegotiate the contract. Welles, however, would not agree without congressional approval. Webb continued the work to maintain receipt-of-progress payments.
As late as December 1865, design work had yet to be completed on the gun ports, which held up the cutting and application of the final armor sections. In May 1866, Monitor designer John Ericsson apparently was retained to provide a solution, and work proceeded. The ship was completed in August 1866, with the Navy making the final of 25 installment payments on 15 August. Her first trial was in September, with acceptance trials yet to be run.
Webb could have pushed the Navy to accept the ship, but he knew it had no use for her, and thus he would have no leverage to renegotiate to reclaim his investment. This also became his bargaining chip. As Webb searched for buyers, he began talks to buy the ship back from the government by refunding its payments. In March 1867, a congressional bill was signed into law releasing “all right, title, interest, and demand of United States” on the Dunderberg in exchange for receipt of the advances.
On 1 May, the ship was sold to France along with the veteran Civil War monitor Onondaga. Webb received $2.5 million from France for his ship and reimbursed the federal government $1.1 million. His profit, however, was significantly less once his added expenditures were deducted.
On 19 July, the Dunderberg set steam and sail for France; renamed the Rochambeau, her service life was brief. After nearly three years of trials and modifications, she was commissioned in the late summer of 1870, decommissioned and stricken on 15 April 1872, and scrapped in 1874. Reportedly, the French had “endless trouble” with the ship.
At the time of her construction, the Dunderberg was innovative. Elements of her construction, unusual and considered unimportant in her time, are today regarded as essential to any seagoing ship. Included among them are double bottoms, collision bulkheads, watertight transverse and longitudinal bulkheads extending from keel to spar deck, fully enclosed water-tight engine and boiler rooms, and air and water pumps independent of the main engines. Nevertheless, she remained the Navy’s great white elephant.