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 a German vessel ) 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
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 of
M-200 died during a failed rescue operation. In July 2015, another M-class (series XII) submarine was found in the Black Sea by divers off the Romanian coast at
Costinești, 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 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, with the conning tower and deck gun intact. In April 2025, after a 20-year search, M-class submarine
M-49 was found in the
Peter the Great Gulf.
M-49 had gone missing on 16 August 1941. ==Versions==