actually the Arkansas did break the blockade...above Vicksburg. it was sent south to co-operate with land forces attempting to retake Baton Rouge.

it fared well against the Carondelet and the Tyler. the Carondelet, which was one of the city class 'ironclads' wasn't actually an ironclad at all but was a partial ironclad. it had iron plates covering the machinery on its sides and the front of the casemate. both of the front quarters, rear quarters and rear casemate were not armored. the Tyler was of course only armored with wood...a 'timberclad'.

lurking below Vicksburg at Baton Rouge was the USS Essex...this monster was completely covered in iron plates and was heavily armed.

Essex vs. the Arkansas? probably the Essex would have prevailed but its not a slam dunk. who knows, if Baton Rouge had been recovered by the South and had the Arkansas survived, maybe Nawlins could have been retaken.

it certainly would have changed the whole strategic situation in the west.