M-class cruiser

The M-class cruisers were a class of light cruisers 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&mdash;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&mdash;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&mdash;construction number 606&mdash;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&mdash;in 1938&mdash;but construction was halted on 19 and 21 September 1939, respectively. Both hulls were broken up on the stocks shortly thereafter.

General characteristics
The first three M-class ships&mdash;M, N, and O&mdash;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&mdash;Q and R&mdash;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&mdash;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 22000 m. The 15 cm guns had a rate of fire of between 6 to 8 45.3 kg rounds per minute, at a muzzle velocity of 875 meters per second (2,871 ft/s). The guns used two propellant charges: a 14.15 kg RPC/38 fore charge and a 23.5 kg main charge in a brass cartridge.

The ships carried four 8.8 cm L/76 anti-aircraft guns 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 19.8 kg 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 12400 m. 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 tubes 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 GERMAN CRUISER Nürnberg: 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 barbettes was 60 mm thick.