Isn't 300 ironclads a BIT high of a number? Like by about 298???
The Brits and the French could have made the North's life a LOT harder. Not only via oceanic commerce, but also with a military presence and threat via Canada (The British) and Mexico (the French).
Yes, the number 300 is an exaggeration.
42 is the correct number, with 76 laid down.
A couple per port was sufficient to block a port.
And, of course, the Union strategy consisted of taking ports.