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?

Context paragraphs:
Japanese ironclad Kōtetsu: Kōtetsu (甲鉄 , literally "Ironclad") , later renamed "Azuma" (東 , "East") , was the first ironclad warship of the Imperial Japanese Navy.  Built in Bordeaux, France in 1864 for the Confederate States Navy as CSS "Stonewall", and acquired from the United States in February 1869, she was an ironclad ram warship.  She had a decisive role in the Naval Battle of Hakodate Bay in May 1869, which marked the end of the Boshin War, and the complete establishment of the Meiji Restoration.

Sir William Martin, 4th Baronet: Admiral Sir William Fanshawe Martin, 4th Baronet, {'1': ", '2': ", '3': ", '4': "} (5 December 1801 – 24 March 1895), was a Royal Navy officer.  As a commander, he provided valuable support to British merchants at Callao in Peru in the early 1820s during the Peruvian War of Independence.  He became First Naval Lord in the third Derby ministry in March 1858 and in that capacity acted as a strong advocate for the procurement of Britain's first ironclad warship.  He went on to be Commander-in-Chief, Mediterranean Fleet and in that role provided important assistance during the Italian disturbances in 1860 and 1861, reformed the system of discipline in his fleet and developed a comprehensive system of manoeuvres for steam ships.

Monitor National Marine Sanctuary: Monitor National Marine Sanctuary is the site of the wreck of the USS "Monitor", one of the most famous shipwrecks in U.S. history.  It was designated as the country's first national marine sanctuary on January 30, 1975, and is one of only two of the thirteen national marine sanctuaries created to protect a cultural resource rather than a natural resource.  The sanctuary comprises a column of water 1 nmi in diameter extending from the ocean’s surface to the seabed around the wreck of the Civil War ironclad, which lies 16 nmi south-southeast of Cape Hatteras, North Carolina.  Average water depth in the sanctuary is 230 ft .  Since its sinking in 1862, the "Monitor" has become an artificial reef attracting numerous fish species, including amberjack, black seabass, oyster toadfish and great barracuda.

USS Monitor: USS "Monitor" was an iron-hulled steamship.  Built during the American Civil War, she was the first ironclad warship commissioned by the Union Navy.  "Monitor" is most famous for her central role in the Battle of Hampton Roads on 9 March 1862, where, under the command of Lieutenant John Worden, she fought the casemate ironclad  (built on the hull of the former steam frigate USS "Merrimack" ) to a standstill.  The unique design of the ship, distinguished by its revolving turret which was designed by American inventor Theodore Timby, was quickly duplicated and established the monitor type of warship.

Ironclad warship: An ironclad is a steam-propelled warship protected by iron or steel armor plates used in the early part of the second half of the 19th century.  The ironclad was developed as a result of the vulnerability of wooden warships to explosive or incendiary shells.  The first ironclad battleship, "Gloire" , was launched by the French Navy in November 1859.  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.  After the first clashes of ironclads (both with wooden ships and with one another) took place in 1862 during the American Civil War, it became clear that the ironclad had replaced the unarmored ship of the line as the most powerful warship afloat.  This type of ship would come to be very successful in the American Civil War.

Italian ironclad Terribile: Terribile was the first ironclad warship to be built for the Italian "Regia Marina" (Royal Navy), and the second member of the "Formidabile" class .  "Terribile" and her sister, "Formidabile" , were both built in France.  A broadside ironclad, she was laid down in June 1860, launched in February 1861, and was completed in September that year.  She was the first Italian ironclad to enter service and was equipped with four 203 mm and sixteen 164 mm guns.

Russian gunboat Opyt (1861): The gunboat Opyt (Russian: Опыт : experience) was the first ironclad warship commissioned by the Imperial Russian Navy.  It was built by Carr and MacPherson at the Baltic shipyard in Saint Petersburg.  English and Russian wrought iron plates 1200 x 1000 mm in size protected the front part of the gunboat.

SMS Friedrich Carl (1867): SMS "Friedrich Carl"  was an ironclad warship built for the Prussian Navy in the mid-1860s.  The ship was constructed in the French "Societé Nouvelles des Forges et Chantiers" shipyard in Toulon; her hull was laid in 1866 and launched in January 1867.  The ship was commissioned into the Prussian Navy in October 1867.  The ship was the third ironclad ordered by the Prussian Navy, after "Arminius" and "Prinz Adalbert" , though the fourth ship to be acquired, "Kronprinz" , was ordered after but commissioned before "Friedrich Carl".

USS Monitor (LSV-5): USS "Monitor" (LSV-5/AN-1/AP-160/MCS-5) was an "Osage"-class vehicle landing ship built for the United States Navy during World War II.  She was named after the original  (the first ironclad warship commissioned by the Navy), and was the second U.S. Naval vessel to bear the name.

SMS Hansa (1872): SMS "Hansa"  was a German ironclad warship built in 1868–1875.  She was the first ironclad built in Germany; all previous German ironclads had been built in foreign shipyards.  She was named after the Hanseatic League, known in Germany simply as "Hanse", Latinized "Hansa".  The ship was launched in October 1872 and commissioned into the German Imperial Navy ("Kaiserliche Marine") in May 1875.  Designed for overseas service, "Hansa" was classed as an armored corvette and armed with eight 21 cm guns in a central battery.

Supporting paragraphs: Monitor National Marine Sanctuary USS Monitor
Answer: 230 ft