The ironclads crossed Stono Bar and entered Charleston Harbor on 6 April, but a heavy fog stopped their advance lest they run aground attempting to negotiate the tricky channels leading to the vital Confederate port.

Shortly after 15:00, Weehawken's guns opened on Fort Sumter, and through the afternoon Du Pont's ships stubbornly hammered at Confederate batteries while withstanding the intense and accurate converging fire of the Southern cannon.

That night, however, reports from his captains of the serious damage suffered by their ships convinced him that the small chance of success of another attack did not justify the great risk to his squadron.

Early in July, after he had taken command of the South Atlantic Blockading Squadron, Rear Adm. John A. Dahlgren ordered the monitors back to Charleston harbor.

Nahant, now under the command of William Kennon Mayo, and her sisters bombarded Confederate works on Morris Island on July 10, supporting and covering the landing of Army troops.

On November 15, she joined Lehigh in supporting the Union Army at Cumming's Point on Morris Island during a heavy evening bombardment from Fort Moultrie.

Life aboard Nahant during the Civil War was documented in a book titled "A Year on a Monitor and the Destruction of Fort Sumter" by Alvah F Hunter.