Which ironclad had the longest viable service life?
Short answerHMS Warrior, because her size left more scope for improvement and adaptation than smaller contemporary ships.
NotesHMS Warrior's size explains her long span of practical viability. Available space is a strategic design resource because new weapons, machinery, sensors, and accommodation all compete for volume. A small ship often has to remove an existing capability before adding another. A larger hull can sometimes accept the change through rearrangement or unused capacity. The higher initial cost of the big ship may therefore buy a longer useful life and more modernization choices.