The Stevens Battery was an early design for a type of ironclad, first proposed in 1841 for use by the United States Navy. A revolutionary design with potential capabilities far beyond the norm for her times, she might have set a new standard in naval design for the time if she had put to sea in the 1840s, 1850s, or 1860s. One full-sized example was begun, but attempts in the following decades to complete the ship to three different designs all failed thanks to extensive construction delays and a lack of funding. Construction finally was abandoned in 1874, and she was sold for scrapping in 1881 without ever being launched.

In 1841, the United States was in the midst of a war scare with the United Kingdom over the American boundary with Canada, among other issues. Americans remembered the British invasion of the United States by sea during the War of 1812 and, to avoid its recurrence, President John Tyler and United States Secretary of the Navy Abel P. Upshur called for a large increase in the size of the United States Navy in order to defend the coast. A like-minded United States Congress authorized the use of US$8,500,000 to fund the expansion.

In this environment, Robert L. Stevens and Edwin Augustus Stevens, the sons of the inventor Colonel John Stevens, proposed to the United States Department of the Navy on August 13, 1841, the construction of a revolutionary steam-powered ironclad vessel of high speed, with screw propellers and all machinery below the waterline. Congress passed and President Tyler signed the Stevens Battery Act the same year to authorize funding for the construction of the ship, and the U.S. Navy's Board of Navy Commissioners approved the Stevens brothers' specific proposal for the ship in January 1842. An act of Congress authorizing Upshur to contract for the construction of a shot- and shell-proof steamer, to be built principally of iron, on the Stevens plan was approved on April 14, 1842. The ship, which became known as the "Stevens Battery," was to be the first such ship ever to be built under United States Government authorization. She was intended to serve as a fast, powerful, heavily armored, mobile battery, reinforcing the coastal fortifications of New York City.

The Stevens brothers selected their family estate in Hoboken, New Jersey, as the construction site for the ship. They had to have a drydock dug out of solid rock there, and then install large pumps to keep the drydock from flooding, and delays occurred from the very beginning of the project. The budget for the ship was set at US$600,000, based on vaguely similar earlier ships, but in fact the new ship was so revolutionary in concept and design that no one really knew how to build her or how much she would cost.

The Stevens's original design for the ship was completed in 1844 and called for a 250-foot-long (76-meter) ship 40 feet (12 m) in beam and displacing 1,500 tons. She was to be armed with six large-caliber muzzle-loading cannons in open casemates on decks, loaded from below the main deck by gun crews protected by armored casemates employing sloped armor to further improve protection. She was to be proof against 64-pound (29 kg) shells, the largest fired by U.S. Navy guns at the time. To achieve this, she was to be armored with 4.5-inch-thick (114 mm) iron plate reinforced by 14 inches (356 millimeters) of locust timber, a thickness of iron and wood believed by the Stevenses to be sufficient to resist any gun then known. Furthermore, she was to be semisubmersible, able to submerge herself to her gunwales to make her a smaller target for enemy gunners. Her steam engines were to produce 900 indicated horsepower (671 kilowatts) and give her an estimated top speed of 18 knots (21 mph; 33 km/h), and this very high speed for the era combined with good maneuverability was intended to make her a hard target to hit as well.

Experiments by John Ericsson with his 12-inch (305 mm) wrought iron gun Oregon, which could fire a 225-pound (102 kg) shell 5 miles (8 kilometers), soon proved that 4.5-inch (114 mm) armor was insufficient. In March 1845, Robert Stevens' health failed and he spent the next two years recuperating in Europe. His absence and the need to rethink the ship's armor scheme led to little work being done on her for several years. In 1851, Secretary of the Navy George Bancroft ordered work on the ship stopped because of her inadequate armor, and Commodore Charles W. Skinner, chief of the Navy's Bureau of Construction, announced his intention to scrap the incomplete ship and sell her materials.

The Stevens brothers succeeded in getting Congress to overrule Bancroft and Skinner, and set about radically redesigning the Stevens Battery. The new design was ready by January 1854. It called for a great increase in the ship's size and capabilities. She was now to be 420 feet (128 m) long, 53 feet (16 m) in beam, and displace 4,683 tons. She was to be proof against 125-pound (56.7 kg) shells, with armor made up of 6.75-pound (3.1 kg) iron plates sloping upwards from 1 foot (0.3 m) below the waterline to the main deck and running along the entire side of the ship from stem to stern. She was to have bulwarks to make her more seaworthy when steaming which could be lowered to reduce her freeboard in combat, making her a smaller target. Again, the ship was to be semisubmersible, able to submerge herself down to the gunwales, also to make her a smaller target.

Her armament was to consist of two 10-inch (254 mm) rifled guns mounted on pivots fore and aft and five 15-inch (381 mm) smoothbore guns mounted on the deck above an armored casemate. The 15-inch (381 mm) guns were to fire 425-pound (193 kg) shells. The gun crews, protected by the casemates, would load the 15-inch (381 mm) guns from below through holes in the deck protected by armored hoods; the gun's muzzle would be pointed into the hole, and a steam-powered cylinder would use a ramrod to load the gun for the next shot, allowing a high rate of fire. Water was to be injected into each gun automatically after it fired, to cool the gun and prevent it from being damaged by extended, rapid firing.