John A.B. Dahlgren was a cannon designer for the US Navy Ordnance Department; he designed the famous cannon that helped decide the War between the States. Two of his famous Dahlgren 11" cannons were the only armament on the USS Monitor
when it fought the CSS Virginia (AKA Merrimack)
on the 9th of March, 1862, the first battle between ironclad warships.
featured Swedish-American engineer John Ericsson''s famous "cheesebox on a raft" design. This 9 x 20 foot revolving turret had only two guns inside; 11” Dahlgren cannons
. These massive rifled cannons were capable of firing a variety of shot, shell, grape-shot, shrapnel, canister, musket and rifle balls. The Monitor''s
turret guns might have done more damage if the pieces had been used as designed, with charges of 20 or even 30 pounds of gunpowder. However, the pressure of the situation made Dahlgren cautious, and he decreed a maximum charge of 15 pounds.
The battle between the Monitor and the Virginia, was considered a tactical draw, but both sides were so impressed with the battle their prospective naval yards were contracted to build more ironclads. The world had seen the end of the days when "the ships were of wood and the men were of iron".