Upon entering service in June 1897, Iowa conducted training operations in the Atlantic Ocean before moving to the Caribbean in early 1898 as tensions between the United States and Spain over Cuba grew, leading to the Spanish–American War.

Conflicting ideas about the vessel that would be built delayed construction and led the Secretary of the Navy, Benjamin F. Tracy, to convene a Policy Board in January 1890.

Tracy wanted to build sea-going battleships that could project American naval power overseas, though significant elements in the Navy and the United States Congress preferred shallow-draft coastal-defense ships.

In addition, the heavy 8-inch gun turrets were moved closer together amidships, which reduced the amount of weight toward the ends of the ship, also contributing to improved sea-keeping.

[10] Six 4 in (100 mm)/40 cal quick-firing guns rounded out the secondary battery; these were intended to use their high rate of fire, coupled with high-explosive shells to damage unarmored parts of enemy warships.

On either end of the belt, the deck sloped down on the sides and was increased slightly to 3 in (76 mm) to provide the bow and stern with a measure of protection against light guns.

After emerging from the dry dock, Iowa sailed for Virginia, alternating between Hampton Roads and Newport News through mid-January, before departing for Key West, Florida.

During this period, Maine exploded and sank in Havana, Cuba; the accidental explosion was initially blamed on a deliberately detonated Spanish naval mine.

Sampson was appointed to serve as President of the Board of Inquiry that was sent to investigate the sinking, so Captain Robley D. Evans took his place as Iowa's commander on 24 March.

Sampson had by this time taken command of the North Atlantic Squadron, which Iowa joined; she took part in the blockade operation from 22 April to 1 May before returning to Key West to replenish fuel.

[12] The Americans searched the harbor at Puerto Rico on 12 May, but found no Spanish warships, and so bombarded the port, focusing their fire on Castillo San Felipe del Morro, an old coastal fortress.

Iowa led the American line of battle on several passes in front of the fort, and she was struck once by a Spanish shell that wounded three men and inflicted minor splinter damage to the ship.

Assuming that Cervera was headed for Havana, Sampson took his squadron there, but while en route he learned that the Spanish had been coaling in Saint Thomas in the Danish West Indies.

Sampson instead decided to take his ships back to Key West, arriving there on 18 May, while Cervera reached Santiago de Cuba the following day.

On the morning of 29 May, lookouts aboard Marblehead reported spotting the Spanish cruiser Cristóbal Colón in the roadstead outside Santiago de Cuba.

Schley made an initial attack on the afternoon of 31 May; he led the line with his flagship Massachusetts, followed by the protected cruiser New Orleans, and then Iowa on a pass in front of Cervera's ships, opening fire at long range at 14:05.

The American shells fell short and they gradually shifted their fire, but they failed to score any hits, though Evans noted that he believed they had inflicted splinter damage.

The approach to Santiago de Cuba was guarded by coastal artillery and mines, which prevented Sampson's ships from breaking into the inner harbor without taking serious damage.

By early July, American troops were beginning to approach the hills outside Santiago de Cuba, threatening the coastal batteries that protected Cervera's ships, and prompting the Spanish command to order him to attempt a break out.

[12] At 08:45 on 3 July, Cervera sortied with his flag aboard the cruiser Infanta Maria Teresa, followed by Cristóbal Colón, Vizcaya and Almirante Oquendo and the destroyers Plutón and Furor.

Iowa quickly got steam in her boilers up to increase speed to close with the fleeing cruisers; the range fell steadily until she was just 2,500 yards (2,300 m) away from Infanta Maria Theresa.

The two ships were about 1,400 yards (1,300 m) apart and Iowa's entire battery opened fire, enveloping her in thick black smoke and hampering her gunners' ability to spot targets.

[12] By this point in the battle, heavy American gunfire had set Infanta Maria Theresa on fire, and, fearing a magazine explosion, Cervara ordered her run aground at 10:25.

Meanwhile, the two Spanish destroyers had also been badly damaged by the American battleships; Indiana had nearly cut Plutón in half with a 13-inch shell, forcing her to run aground, where she exploded.

On 20 July, four days after the Spanish garrison at Santiago de Cuba surrendered, Iowa suffered a boiler accident while she was patrolling off the city.

The crew set a board across a bucket and Fireman 2nd Class Robert Penn climbed across to shut off the boiler, risking being badly burned, and he was later awarded the Medal of Honor for his actions.

Captain Silas Terry took command of the ship on 24 September and on 12 October, she departed for the West Coast of the United States, where she was to join the Pacific Squadron.

Iowa then sailed north to New England, visiting several ports, including Provincetown, Newport, Bar Harbor, Boston, and New York over the course of the next four months.

Iowa then steamed north to Annapolis to participate in the ceremonial return of John Paul Jones after his remains had been exhumed from his original grave in Paris so they could be re-interred at the US Naval Academy.

She next went to sea in April 1922 for shooting practice off the Virginia Capes with Shawmut now serving as her control ship, but the exercises were cancelled and she returned to port.