In early 1862, the Union and the Confederacy were locked in one of the most influential arms races of the Civil War. While their navies still relied on wooden ships, both sides had gambled on building revolutionary “ironclad” vessels that boasted steam engines, hulking cannons and armor plating protecting their hulls. In Brooklyn, Federal forces were prepping the iron vessel USS Monitor. At Gosport Navy Yard in Portsmouth, Virginia, the rebels were finishing their own metal colossus, CSS Virginia.

The Union’s Monitor was by far the more unusual of the two craft. Designed by Swedish-born engineer John Ericsson, the ship was around 173 feet long and featured a main deck that sat just 18 inches above the waterline. Its armaments were limited to two 11-inch Dahlgren guns, but they were housed in a revolving turret powered by a steam engine. This never-before-seen feature gave the ship’s gun crews a 360-degree range of fire.

In contrast to the nimble and innovative Monitor, the Confederacy’s Virginia was the maritime equivalent of a wrecking ball. Improvised from the ruins of the ruined American frigate USS Merrimack, the 275-footer was constructed from wood reinforced with four-inch-thick iron plate. Its most eye-catching feature was a large, sloping casemate that housed a floating battery of 10 cannons—four on each side and one at both ends. The ship’s bow bristled with a 1,500-pound iron battering ram.

Neither of the ironclads was much to look at—the Monitor was labeled a “tin can on a shingle” and the Virginia a “floating barn roof”—but critics were silenced the minute their destructive power was put on display. On March 8, 1862, the Virginia left Gosport on its maiden voyage and steamed toward nearby Hampton Roads, a vital sea junction that was patrolled by a Union blockading fleet. As the ironclad neared the Federals’ wooden flotilla, Confederate commander Franklin Buchanan addressed his crew. “Sailors,” he announced, “in a few minutes you will have the long-expected opportunity to show your devotion to your country and our cause.”

The men of the Union blockading fleet had heard rumors about the “great Southern bugaboo” lurking at Gosport, but nothing could have prepared them for actually facing the Virginia in combat. At around 2 p.m., the ironclad entered Hampton Roads and made a beeline for the American ships USS Cumberland and USS Congress. The Congress unleashed a broadside, but its cannonballs bounced harmlessly off the Virginia’s metal armor. Ignoring the enemy guns, Buchanan steamed toward the Cumberland and plowed into it with his ram, cleaving a seven-foot-wide hole in its hull. The Cumberland instantly began to sink, and it nearly took the Virginia down with it before the ironclad’s ram broke off. When the crippled Cumberland refused to surrender, the Virginia pummeled it with cannon fire. “The once clean and beautiful deck was slippery with blood, blackened with powder and looked like a slaughterhouse,” one Cumberland crewman later remembered.

While the Cumberland sank, the Virginia turned its attention to USS Congress, which had intentionally run itself aground in shallow water to avoid being rammed. Despite knowing that his own brother was among its crewmen, Buchanan raked the Congress with cannon fire for several minutes, inflicting horrific casualties and eventually setting it ablaze. The ironclad would have moved on to the steam frigate USS Minnesota, which was also grounded in the shallows, but after Buchanan was wounded in the thigh, acting commander Catesby Jones elected to call off the attack and return the following morning. By then, the Virginia had sunk two Union ships and killed over 240 sailors. The battle would remain the bloodiest day in U.S. naval history until World War II.

The Virginia’s rampage had been a serious blow to the Union navy, but the remainder of the blockading fleet soon received an imposing reinforcement. On March 6, the ironclad USS Monitor had left Brooklyn and sailed south under the command of Lieutenant John Worden. By dawn on March 9, its sleep-deprived crew had arrived in Hampton Roads and positioned their vessel alongside the stranded Minnesota. “I will stand by you to the last if I can help you,” Worden vowed to the Minnesota’s captain.

Later that morning, having steeled his crew with a ration of two jiggers of whiskey per man, the Virginia’s acting commander Catesby Jones steered his ship back into Hampton Roads to finish off the Minnesota. It was only when he neared the grounded vessel that he noticed the Monitor floating alongside it. The rebels initially mistook the peculiar looking ironclad for a raft or even a ship’s boiler, but they quickly set aside their surprise and let loose with the first cannon salvo of the day. Moments later, the Monitor replied with a burst from its twin Dahlgren guns.

For the next three hours, the Monitor and the Virginia engaged in a ferocious cannon duel—the first ever waged by ironclad warships. “The fight continued with exchange of broadsides as fast as the guns could be served and at very short range, the distance between the vessels frequently being not more than a few yards,” the Monitor’s executive officer Samuel Dana Greene later wrote. The waters of Hampton Roads soon filled with the groan of steam engines, the thunderclap of naval guns and the clang of cannonballs ricocheting off iron plate. Inside their sweltering and smoke-filled metal machines, the gun crews of both ships worked frantically to fire and reload their cannons. Virginia’s chief engineer Ashton Ramsay later noted that the hellish scene could only be compared “with the poet’s picture of the lower regions.”

Both ship’s armor plating fared well under the constant barrage of cannon fire, but their crews soon ran into technical problems. The Monitor’s revolving turret continued to turn, but its operator could not easily stop it, which forced the gunners to fire on the fly. The Virginia, meanwhile, was finding it difficult to outmaneuver the faster and more agile Monitor. At one point, the Confederate ironclad even briefly ran aground in shallow water and had to push its engines to the breaking point to dislodge itself. Sensing that his guns were causing no serious damage to the Monitor, Jones eventually tried to ram it. The Virginia succeeded in colliding with the Yankee ship, but having lost its iron ram the previous day, it was unable to deal any significant damage.

The battle raged all morning with no clear advantage for either side. “Shot, shell, grape, canister, musket and rifle balls flew about in every direction,” the Monitor’s Greene wrote, “but did us no damage.” Finally, at around 12 p.m., the Virginia’s gunners fired a blast that struck the pilothouse near the Monitor’s bow. Worden had been peering out the pilothouse’s iron shutters at the time, and he was left temporarily blinded by powder and debris. “I cannot see, but do not mind me,” he told Greene as he was carried away. “Save the Minnesota if you can.”

The Monitor had pulled away from the battle while the crew saw to Worden’s injury, yet to the Virginia, it appeared that the Union ship was giving up the fight. Catesby Jones was still eager to sink the Minnesota, but with the tide turning and his enemy seemingly in retreat, he decided to withdraw. When the Monitor finally tried to rejoin the battle, the Virginia had already started steaming back to Portsmouth for repairs. At that, the first ever clash of ironclads came to a sudden and inconclusive end.

Both the Union and the Confederacy would later claim victory in the Battle of Hampton Roads, but most historians now consider the contest a tactical draw. The fact that neither one of the ironclads had managed to destroy the other proved to be the most significant lesson of the fight. In the span of a morning, the Monitor and the Virginia had brought an end to the age of wooden warships. After hearing about the slugfest, navies around the globe devoted themselves to building steam-powered ironclads. The Confederacy and the Union would eventually launch over 70 of the metal behemoths before the Civil War ended.

Neither the Monitor nor the Virginia lasted long after Hampton Roads. During the Confederate evacuation of Norfolk in May 1862, the Virginia’s crew intentionally blew up their ironclad to prevent it from falling into Yankee hands. Later that same year, the Monitor sank in rough seas off the coast of North Carolina. Both ships’ careers had lasted less than a year, but for those who witnessed their historic duel, it was evident that sea combat would never be the same again. “This successful and terrible work will create a revolution in naval warfare,” wrote one Southern reporter, “and henceforth iron will be the king of the seas.”