Question: What is the water depth of sanctuary which is the site of the wreck of the first ironclad warship commissioned by the union navy?
Sentence (from "Ironclad warship"): The British Admiralty had been considering armored warships since 1856 and prepared a draft design for an armored corvette in 1857; in early 1859 the Royal Navy started building two iron-hulled armored frigates, and by 1861 had made the decision to move to an all-armored battle fleet.
Relevant evidence: No