M - class cruiser The M - class cruisers were a class of light cruiser s planned , but never built , by the German Navy before World War II . The ships were designed for commerce raiding in the Atlantic Ocean . The design for the first three ships suffered from a number of problems , and so the fourth and fifth ships were substantially redesigned . The name of the class is taken from the letter designating the first projected unit . As long as the ships were not named , they were referred to by letters assigned in the chronological order of their planned construction . The first planned unit would have been the thirteenth German cruiser and was therefore listed as " cruiser M " in the navy ' s documents . Had any of the ships been built , the class would have been named after the first completed unit . Development and cancellation . The M class was intended for use as a scout for the commerce raiding squadrons envisioned under Plan Z . The ships design process started in 1936 ; the ships were intended for long - range commerce raiding . They were an improvement over previous designs , which suffered from insufficient range to be effective commerce raiders . However , the requirements placed on the design — high maximum and cruising speeds , long range , heavy armament , and armor sufficient to withstand 15 cm shells , all on a displacement no more than 8 , 000 metric tons — were deemed impossible by the design staff . In July 1937 , the " Oberbefehlhaber der Marine " ( commander in chief of the navy ) requested proposals from both the naval design staff as well as private dockyards . None of the designs by the dockyards were practical , and so the official design , which only met some of the requirements , was chosen . During further development of the design , serious flaws became apparent , including the weakness of both the main battery and anti - aircraft armament , as well as the insufficiently thick armor protection . The stepped arrangement of the deck armor wasted space and was therefore impractical . The layout of the propulsion system was also problematic ; both turbines were in the same engine room , and therefore each were vulnerable to disabling if the other was damaged . Their crew spaces were also insufficient for long - range cruises . As a result , the design was heavily modified for the last two ships of the class , " Q " and " R " . The initial design borrowed on contemporary British and French ships , the and , respectively . The distribution of the M - class ships ' side armor was the most obvious influence of the " Southampton " - class design . The contract for " M " was assigned to " Deutsche Werke " in Kiel under the construction number 263 . " N " followed at the " Kriegsmarinewerft " in Wilhelmshaven , as number 129 . " O " — construction number 606 — was assigned to " Germaniawerft " in Kiel , but on 8 August 1939 , the contract was transferred to the Kriegsmarinewerft . " P " was also assigned to " Germaniawerft " , under number 607 . " Q " was assigned to Schichau in Danzig , and the contract for " R " was awarded to the " Deutsche Werke " . Only the keels for " M " and " N " were laid — in 1938 — but construction was halted on 19 and 21 September 1939 , respectively . Both hulls were broken up on the stocks shortly thereafter . Design . General characteristics . The first three M - class ships — " M , N , " and " O " — were 178 meters long at the waterline , and 183 meters long overall . They had a beam of 17 meters and a draft of 5 . 42 meters standard , 7 . 25 meters forward , and 6 . 03 meters aft . The ships had a designed displacement of 8 , 500 metric tons , but displaced 7 , 800 tons at standard load and 10 , 400 tons fully laden . The ships had a crew of 28 officers and 892 men . They were designed to carry one picket boat , a barge , a launch , and two cutters . The last two ships — " Q " and " R " — were enlarged versions : 188 meters long at the waterline and 196 m overall . Their beams were 1 meter wider , at 18 meters . The ships ' draft was lower at 5 . 4 meters . The ships were designed to displace 9 , 300 tons , and displaced 8 , 568 tons standard . All six ships were to have steel - made , and up to 85 % welded construction . The design called for fifteen watertight compartments and a double bottom for 78 % of the length of the hull . All six ships were intended to use two sets of Brown , Boveri , & Co . and Wagner turbines or Marine - type turbines built by Germaniawerft and four MAN double - acting 12 - cylinder two - stroke diesels . " R " , however , was equipped with an additional four diesels , for a total of eight . The turbines were powered by four Wagner ultra - high pressure boilers , designed to put out 58 atmospheres of pressure . The propulsion system drove three screws , although four were considered for " Q " and " R " . The ships ' electrical power was supplied by four generators that produced 2 , 400 kW at 220 volts . Armament and armor . All six ships were armed with the same set of weaponry . The primary armament consisted of eight 15 cm L / 55 quick - firing guns mounted in four twin turrets , in superfiring pairs fore and aft . The guns had a total of 960 shells , for 120 rounds per gun . The 15 cm twin turrets were Drh L . C / 34 mounts — the same type as those fitted to the - and s , as well as a number of other designs . The turrets allowed depression to - 10 degrees and elevation to 40 degrees , which enabled a maximum range of . The 15 cm guns had a rate of fire of between 6 to 8 rounds per minute , at a muzzle velocity of 875 meters per second ( 2 , 871 ft / s ) . The guns used two propellant charges : a RPC / 38 fore charge and a main charge in a brass cartridge . The ships carried four 8 . 8 cm L / 76 anti - aircraft gun s in two twin turrets , aft of the main superstructure . The 8 . 8 cm guns were supplied with 1 , 600 shells , for 400 rounds per gun . These guns fired high explosive shells at a rate of fire of 15 to 20 rounds per minute and a muzzle velocity of 950 m / s ( 3 , 117 ft / s ) . The guns could elevate to 80 degrees , which allowed them to hit targets flying at . The M - class ships were also equipped with eight 3 . 7 cm AA guns in twin mounts centered around the superstructure . They had a total of 9 , 600 shells . The anti - aircraft weaponry was supplemented with four 2 cm guns , each of which had 2 , 000 rounds . The ships were also armed with eight deck - mounted torpedo tube s and approximately 60 mines . The ships were to have been protected with Krupp and " Wotan , Hart " ( " Wotan " , Hard ) armor plating . The class decks were 20 mm thick , with 35 mm thick sloped deck . The conning tower had a roof that was 50 mm thick and sides 100 mm thick . The inner layer of the armor belt was 50 mm thick in critical areas amidships , and tapered down to zero protection at the stern and bow . The outer layer was 30 mm amidships ; it too tapered down to nothing at both ends of the ships . The gun turrets had the same armor protection as the preceding light cruiser : the sides were 35 mm thick , the faces were 80 mm thick , the roofs ranged in thickness from 20 – 35 mm . The armor protecting the turret barbette s was 60 mm thick .