The development of ironclad vessels had been under way for some time; the first steam frigate had been designed by Robert Fulton and built in New York Harbor in 1815. But manufacturers and governments alike continued to believe in the power of the sailing navies, and development was therefore slower than might be expected.

Under a rush contract, a firm in Brooklyn turned out the USS Monitor, which many observers likened to a cheesebox resting atop a raft. Extremely low to the water, the Monitor had a turret rather than traditional gun placements: its two cannons could therefore be rotated. This novel device was thanks to the Swedish inventor John Ericsson. When one first viewed the Monitor, the sight provoked laughs, giggles, and expressions of disbelief. But the little cheesebox was about to demonstrate its worth.