What is the most modern ship HMS Warrior could fight on roughly equal terms?
Short answerProbably a pre-First World War gunboat. Treaty-era examples are considered first, but their modern guns may already make them too powerful for a fair contest.
NotesA fair opponent depends on speed, gun power, protection, and fire control. A small gunboat could penetrate Warrior's armour yet remain vulnerable to her full broadside, especially if it could not outrun her. The Dragonfly class is considered with a quoted speed of 17 knots and two 4-inch guns. The Insect class's 6-inch guns make an equal contest more doubtful. After comparing those weapons, the final estimate shifts back toward a pre-First World War gunboat, without settling on a particular ship.