Did the Union Navy have anything that could realistically challenge HMS Warrior during the American Civil War?
Short answerNot on the open sea; only a concentrated ambush in confined waters offered a plausible chance, and Warrior need not enter them.
NotesNo Union ship could challenge HMS Warrior on the open sea. A plausible chance appears only in narrow water, where several American vessels could ambush her at close range. The Royal Navy could avoid that trap and send other ships into the confined approach. The comparison turns on forcing Warrior into a restricted environment rather than meeting her in open water.