Soviet M-class submarine
The M-class submarines, also "Malyutka" class (; "baby" or "little one"), were a class of small, single-, or 1½-hulled submarines built in the Soviet Union and used during World War II. The submarines were built in sections so they could easily be transported by rail. The production was centered in the Gorky Shipyard on the Volga River, after which the sections were transported by railway to Leningrad for assembly and fitting out. This was the first use of welding on Soviet submarines. History. 1930s to 1940s. Submarines of this class were in four series: VI, VI -bis, XII, XV. The number of VI and VI-bis series boats were almost equal. Series XII was a re-developed project with equivalent tactical characteristics. The first series were powered by one diesel engine and one electric motor. Series XV had developed separately with improved characteristics, including the main ballast in light hull and two shafts. These vessels were mainly used by the Black Sea Fleet and the Baltic Fleet. Although the design was satisfactory, only limited results were obtained and losses were heavy with 33 submarines sunk between 1941 and 1945. "M-103" disappeared in the Baltic Sea in  mid-August 1941. The wreck was discovered in the late 1990s during a NATO minesweeping training exercise. Seven submarines were lost in the Black Sea, four depth-charged and sunk by Romanian warships ("M-31" by the flotilla leader , "M-58" by the destroyer "Regina Maria", "M-59" by the destroyer "Regele Ferdinand" and "M-118" by the Romanian gunboats "Ghiculescu" and "Stihi")(both "M-58" and "M-59" however are also reported as lost on Romanian laid mines, while "M-31" was also claimed by mines or German boat ) and three were sunk in minefields laid by the Romanian minelayers , "Dacia" and "Regele Carol I". By 1945 , some 111 M-class submarines had been completed, with another 30 XV-series completed between 1945 and 1947. Cold War. Two submarines of the early series of this class, along with two s, ("S-52" and "S-53") and two s (under lease, "S-121" and "S-123") were sold to the People's Republic of China in June 1954 as the foundation of the People's Liberation Army Navy Submarine Force. Both the M- and S-class submarines were sold to China, and two more M-XV series of this class ("M-278" and "M-279") were sold to China a few years later in  1956.Those purchased by China were renamed, but the two leased "Shchuka"-class submarines were not. The four M-class submarines bought by China were renamed National Defense # "21", "22", "23" (ex "M-278") and "24" (ex "M-279") respectively. Modern times. An M-class submarine was discovered near Tallinn in May 2012. The submarine is located in the Tallinn Bay between the islands of Aegna and Naissaar, at an approximate depth of . It is believed to be "M-216", which was intentionally sunk in the area in 1962 for training purposes. Divers have confirmed that many components, including the periscope, are missing. It is  also believed that the training exercise may have been ordered as a result of several deadly submarine accidents in the 1950s. One such accident happened near Paldiski, where the entire crew died during a failed rescue operation. Another M-class (series XII) submarine was found in July 2015 by divers from Aquarius Dive Center Constanta, in front of Costinesti, at an approximate depth of . It is believed to be either "M-34" or "M-58", both being lost to Romanian minefields. The submarine is buried in the sand up to the deck level, and also completely filled with sand, making any further  identification almost impossible. The upper part of the hull shows a pretty high level of damage - many ribs are exposed. The aft hatch was partially opened. The hull is in one piece, conning tower and deck gun intact. Completed after World War II: Versions. Both series VI and VI-bis were constructed by A. N. Asafov. Series XII was made by P. I. Serdyuk and series XV was created by F. F. Polushkin.