Tekkosen (armored warships) (鉄甲船)
A tekkosen was a large-size Atake-bune (a type of naval warship) that Nobunaga ODA ordered Yoshitaka KUKI to build in order to fight against the Mori/Murakami navy.
It is said that the entire ship was covered with fireproof iron plates to prepare against attacks by horoku-hiya (one type of fire arrows) at which the Murakami navy was good.
Whether it really existed or not is under discussion.
Summary
One theory says that it was a huge ship of 139 cubic meters in loading capacity with 21.8 to 23.6m in length and 12.7m in width, equipped with three ozutsu (Japanese artilleries) and many odeppo (big guns) and the surface of the body was tacked with iron plates 3mm in thickness. It was also called a Big Atake-bune.
Ships used in the battle of the Kizugawa river are described in Shinchoko-ki (Biography of the Warlord Oda Nobunaga), Tamonin nikki diary, Organtino's report and so on, but realities in detail such as its measurements/equipments are unknown. Even the data in Shinchoko-ki, Organtino's report and so on, which reported the ship comparatively in detail, included no description of the armor, so it is unknown how the ship was armored with iron. Tamonin nikki diary alone reported it as "an iron ship that no bullets of a gun can pass through", which part can be interpreted that it was a ship whose hull was iron-covered in the light ofdocuments of the same period. Gnecchi-Soldo Organtino, a missionary, wrote in his report to Luis Frois that the ship was like one in the Kingdom (Portugal) and that he was surprised to know that such a ship had been constructed in Japan. Six ships were built in Ise for sea barricades by Yoshitaka Kuki, who was ordered by Nobunaga Oda； it is said that the Oda navy with these ships, on the way to Osaka Bay, defeated the Saiga/Taniwa navy, and also destroyed 600 ships of the Mori navy fleet only with six ships. This could be attributed to the steering of Yoshitake, who trained himself in the rough sea of Ise. Legends say that after Nobunaga's death, they were anchored in Osaka Bay and left until it went rotten, or they were dismantled into several small ships.
From the official bakufu documents it is confirmed that the "Atake Maru", the largest Ataka bune in history, which Hidetada TOKUGAWA ordered Tadakatsu MUKAI, the chief of the bakufu navy to build, had all oars and the whole hull covered with copper plates for the prevention of fire and erosion, which proves a definite fact that an idea of covering the surface of a warship existed in 1635.
There exists another example that a large ship, which was about 55m in length, about 13m in width, and equipped with 100 oars and watchtowers at the bow and the stern, was built in Sawayama, the lake side of Biwako Lake in 1573 on the order of Nagahide NIWA (from Shincho-koki). The camouflage was made by Mataemon OKABE, a castle carpenter, who took charge of Azuchi Castle. The ship is said to have been used for the traffic to Kyoto from Otsu or Sakamoto. It is not certain whether this ship was an iron plated one.
In later years the Kuki family in Ominato (Ise City) in Ise built an Atake-bune virtually equivalent to a tekkosen and named ""Oniyado", and Hideyoshi TOYOTOMI, who liked the magnificence of the ship, adopted it as a flag ship in the Bunroku-keicho War, put a madder streamer and an Uma-jirushi (commander's flag) of a golden fan on it as a token of a flag ship, and renamed it "Nippon Maru".
The ship is said to have been 1500 koku (139 cubic meters) in loading capacity, 34m in length, 9.5m in width, had a capacity of 180 crew members and was equipped with 100 oars.
The Nippon Maru was put into commission as an active-duty warship in the early Edo period, but it was remodeled into a smaller ship with 500 koku (139 cubic meters) in loading capacity and 60 oars, and again renamed "Dairyu Maru". It is said that after it was named "Dairyu Maru", a sculpture of a dragon head was newly added to its prow.
As mentioned above, the Edo bakufu built the Atake Maru, the largest Atake-bune in history which was covered with copper plates based on the same idea as a tekkosen. Iron plates would become eroded so easily by sea water that they were unfit for a long-term use, therefore, they were substituted by copper plates, which can be said to have made a reasonable development from a tekkosen. However, it was dismantled in 1682 due to financial difficulties of the bakufu, leading to the end of tekkosen line ships.
Questions about tekkosen
It is estimated that the power of a tekkosen, like ordinary Atake-bune, came from oars and retractable cotton sails, but it is unclear whether a ship with more weight due to iron plates could run at a practical speed using this method.
Although it navigated to Osaka Bay via the Kumano-nada Sea from Ise, some people doubt that a ship that was extremely heavy because of iron plates could pass through the rough Kumano-nada Sea.
It is also uncertain whether the blockade of the Kizu-gawa River was really possible with these six ships as main force.
The Mori navy, which was defeated in the second battle of Kizugawaguchi, started active movements such as carrying army provisions into Miki-jo Castle the next year, which makes the runaway victory recorded in Shincho koki doubtful.