In December of 1863, the Confederate States of America contacted the L'Arman ship building firm in Bordeaux, France to construct one or two ocean-going Ironclad Rams for 2.4 million francs per ship during the Civil War in America. These ships were constructed of mainly of wood with iron plating on the outside hull. Two gun towers were fitted on the deck were also armored for both gun and crew protection. The two towers were designed for - and would receive - three heavy guns: 1 x 10-inch caliber and 2 x 6.4-inch caliber, both produced by the British armaments Armstrong & Company. The two gun towers were 14 inches wider than designed and required that the gun carriages be shortened. The builders had trouble with the ships draught as the extra weight of the armor had been molded incorrectly and also hampered the intended 10.5 knot speed (12 mph). As such, they had to be reforged.
Her coal bins were designed to carry some 280 tons but, after construction, the area was actually limited to just 200 tons. This was deemed unacceptable so additional bin space was provided to hold an additional 20 tons. When the onboard coal ran was all used up, and a coal ship or resupply station was unavailable, the ship could revert to sail propulsion by way of two main masts. The coal could be stretched by using only one engine with the speed reduction lowering the maximum to 5.8 knots. The two boilers were not fitted below the water line as promised but were instead situated between the coal storage compartments and protected by the armor. Fully-loaded and armed, the vessel was a 1,535 ton ironclad ram.
The design resembled the first ocean-going ironclad that was also of French origin - launched in 1859 as the "La Glory". The newer sister ships were 187 feet long and their beam was out to 32.8 feet with the draught running at 14.3 feet. The two vessels were constructed by French L'Arman and consisted of the "Sphynx" (set aside for the CSS) and her sister ship, the "Cheops", which was in the process of being sold to Prussia. The French Government learned that the Sphynx was being built for the Confederate Navy and, being concerned about the political relationship with the current US Government, France blocked the sale in February of 1864. Denmark authorities became interested and purchased the Sphynx and also tried to acquire the Cheops because of their war with Prussia. Denmark was in a hurry and stipulated that the impending sale would require the Sphynx to be in a Danish port within 75 days. She was, therefore, completed and ready to set sail with a Danish crew as quickly as possible.
The Sphynx was renamed the "Saerkodder" (or "strong otter") by the Danish government and set sail for Copenhagen. The shakedown cruise exposed some early problems: she drew too much water - one foot aft and 6.5 inches on center line. The ship was well-built and was considered quite strong and her cannon were notably powerful. The engines were good, however, the Danish captain noted the armor plates being of minimum thickness and poorly fitted. The ship did not have enough room in the aft gun tower reducing the field of fire abeam. The design also did not fare well in high seas and, overall, her main deck had limited room leading to complaints from the crew about their general quarters. These problems lead to price-haggling between the Danes and L'Arman, ultimately resulting in negotiations breaking down. As such, the Danes ultimately refused to accept the Saerkodder in her current form.
Left without a buyer, L'Arman contacted the original buyers at the Confederate Navy which led to some clandestine meetings to arrange a purchase. On January 6, 1865 a Confederate crew came aboard at Copenhagen under the command of CSN Captain T. J. Page. At sea, the ironclad was recommissioned as the CSS Stonewall after southern General "Stonewall" Jackson. In need of supplies before setting out to hunt for Union shipping, the Stonewall returned to France. After being supplied for the mission ahead, she steamed for Maderia in the Azores for coaling before returning to American waters. En route a strong gale hit the ship and, as she maintained poor sea-keeping abilities, the resulting damage produced a leak. She was then forced to seek a safe harbor in Ferrol, Spain. The USS Niagara, a 5,540-ton steam screw frigate, accompanied by the USS Sacramento, a 2,100-ton steam screw sloop, were in port at the time and confronted the CSS Stonewall. A standoff was expected between the wooden-hulled US Navy ships and the CSS ironclad.
Having the leak repaired, the CSS Stonewall was eager for battle but could not corner the federal ships and, concerned about being bottled up in a foreign port, she left for the open sea once more. The Union ships followed at a safe distance and Captain Page turned to challenge the USS Kearsarge and the USS Sacramento only to see them turn and refuse the engagement. Stonewall then set sail for Lisbon, Portugal on March 24th, 1865 to resupply and take on new coal stores for the journey across the Atlantic. His first mission would be to target General Sherman's forces at Port Royal and protect South Carolina.
After leaving Lisbon, the CSS Stonewall crossed the Atlantic. On May 6th, 1865 she made it to Nassau and then made sail for Havana, Cuba where Captain Page was told the Civil War was over. It was decision time for Page - if he were to leave Cuba to make a run to a southern port and was confronted and captured by US Navy ships, he would have to surrender or be considered a pirate subject to hanging. As he was in a neutral port with no way home for his crew he decided to turn over the ironclad to the Spanish Captain General of Cuba for the sum of $16,000. The Spanish delivered Stonewall to the United States Government in July of 1865 and sold the Stonewall to the American Navy for the same amount.
Now in federal hands, Stonewall faced decommissioning and was laid up at the Washington D.C. Naval Yard. There she sat for over two years while she was offered up for sale internationally. The Ezo Tokugawa Shogunate became interested as they were on a war footing with the Imperial Japanese government during the Meji Restoration. However, the hostilities had not broken out yet and, in 1868, the sum agreed upon was $30,000 down and $10,000 upon delivery in Japan. A small American training crew was brought onboard and sailed with the new Japanese crew. During the long shakedown voyage, the conflict broke out between the Ezo and the Japanese government in what became known as the Boshin War. When the now-christened "Kotetsu" (or "Ironclad" in Japanese) arrived in Tokyo Bay, she was flying the Japanese flag. The American training crew reported to the Ambassador and was told to retake the ship with some navy men stationed in Japan and put her back under the American flag and remain onboard as a caretaker crew. America, and the rest of the western powers, took a neutral stance, removing their military advisors and denying war material to the two warring factions.
However, in February of 1869, the Kotetsu transfer was completed and the ship was delivered to the new Meiji government. The decision probably won the war for the Imperial forces as the Ezo Tokugawa Shogunate had first ordered the Ironclad from the United States and the ship was withheld. America had become the king maker.
Kotetsu immediately sailed with a squadron of seven warships towards the island of Hokkaido to attack the Shogun's naval forces. On March 25th, 1869 the Naval Battle of Miyako Bay began when the major warship of the Republic of Ezo, the Kaiten, rammed her prow into the port side of Kotetsu. Kaiten started firing her guns pointblank into the Kotetsu while her Samurai warriors tried to board the ironclad. The main problem was the Kaiten was about nine feet higher than the Kotetsu, slowing the samurai progress. The invaders were killed as they tried to board, finding certain death at the barrel end of a Gatling gun trained on them from the Kotetsu. The Kaiten was able to destroy three of the Imperial fleet ships but was not able to overcome the ironclad herself.
The last major naval battle of the war was the Battle of Hakodate Bay. The Imperial fleet, including Kotetsu, supported the landing of troops on the island of Hokkaido. The landing party destroyed the shore fortifications and attacked the rebel ships with onshore cannon and ships in the bay. On May 4th the rebel ship Chiyodagata was captured by Imperial forces after grounding on the shore. The flagship of the rebel forces, the Kaiten, was hit by many shells from Kotetsu and ultimately put out of action. The rebel ship Banryu managed to sink the Imperial ship Choyo and Kotetsu fired on the Banryu in response, sinking her with heavy damage inflicted. The Imperial Japanese Navy won the battle leading to the surrender of the Republic of Ezo on May 25th, 1869. The ironclad, it seems, was the deciding factor.
Kotetsu was renamed "Azuma" in 1871 and remained in military service until 1888 by which time she was turned to a noncombat harbor ship charged with training naval forces. After her time, she was scrapped.
The Sphynx's/Kotetsu's sister ship - the Cheops - was eventually sold to the Prussian Navy and became the Prinz Adalbert.