L 20 α-class battleship

L 20 α was a design plan for a class of battleships to be built in 1918 for the Kaiserliche Marine during World War I. The design was selected on 2 October 1917, and construction was to have started 11 September 1918. The ships would have been significantly larger than the preceding s, at 238 m (781 ft) long, compared to 180 m (590 ft) for the preceding ships. The ships would have been the first German warship to have mounted guns larger than 40.6 cm (16 in). However, Germany's declining war situation and the transfer of emphasis within the Navy from capital ships to submarines meant that the ships would never be constructed.

Design
In January 1916, Vice Admiral Reinhard Scheer became commander in chief of the High Seas Fleet. Following the Battle of Jutland on 31 May – 1 June 1916, Scheer pushed for new, more powerful battleships. He demanded the new ships have guns of 42 cm (16.5 in) caliber, an armored belt 350 mm thick, and be capable of speeds of up to 32 kn, all on a displacement of up to 50000 MT. The new 42 cm gun was designed by 29 December 1916, and was approved on 11 September 1918, though none were actually built. After the outbreak of unrestricted submarine warfare in February 1917, Admiral von Capelle argued that capital ship construction should not be halted in favor of U-boat construction. On 21 August 1917, the construction department submitted two design proposals for the new battleship class, L 20 and L 24. The primary difference was the placement of the ships' torpedo armament. The L 20 design placed them in the hull below the waterline, while the L 24 proposal used above-water launchers. Displacement for the designs was fixed at 45000 MT. Both ships also had a top speed of only 23 kn, which was unacceptable to Scheer.

During the design process, it was decided that the utmost concern was that the ships could be built quickly and placed into service. The ships were to discard the use of broadside belt armor below the waterline, the attachment of which was an extremely long process. It was believed that the higher speed of the class—26 kn—would make up for the vulnerability to torpedo attack and make the armor unnecessary.The initial designs called for three main battery turrets, each mounting a pair of new 42 cm (16.5 inch) guns, though this was later increased to four twin turrets. However, the work that would have been necessary to design and test the new turret clashed with U-boat construction, which had become the priority of the Navy. Krupp, the firm that had been awarded the contract to conduct the testing, informed the Reichsmarineamt (RMA—the Imperial Navy Office) that design work on the new turret would have to wait. Capelle accepted the news without much objection. The RMA filed a report dated 1 February 1918, which stated that capital ship construction had ground to a halt, primarily due to the shifting priorities to the U-boat war.

Armament
The main battery was arranged in four twin turrets, as in the preceding, in a superfiring arrangement on the centerline. The aft pair of turrets were separated by engine rooms. The four turrets mounted two 42 cm (16.5 in) SK L/45 guns, for a total of eight guns on the broadside. The 42 cm gun fired a 1000 kg shell out to 33000 m at the maximum elevation of 30 degrees. The estimated muzzle velocity was 800 m/s The ships were to have been armed with a secondary battery of twelve 15 cm (5.9 in) guns mounted in casemates. The anti-aircraft battery was to have consisted of either eight 8.8 cm (3.45 in) Flak L/45 guns or eight 10.5 cm (4.1 in) Flak L/45 guns. The design was to have been equipped with three submerged torpedo tubes, either 60 cm (23.6 cm) or 70 cm (27.6 in) in diameter. One tube was placed in the bow, the other two on either beam to the rear of the engine rooms.

Armor
The ships had a 350 mm armored belt, and ran from slightly forward of the fore barbette to slightly aft of the fourth barbette. The belt began 35 cm below the waterline to 195 cm above it. Directly above the main belt was a strake of armor plating that was 250 mm thick. This section of side armor extended up to the upper deck. The ships' armored deck was to have been 50 mm thick forward, increased to 50 to 60 mm amidships, and 50 to 120 mm aft. The ships were also to have had a forecastle deck that was 20 to 40 mm thick. The ships were also protected by a torpedo bulkhead that was 50–60 mm thick. A sloped 30 mm thick splinter bulkhead, designed to protect against shell fragments, extended from the top of the torpedo bulkhead up to the upper deck.

The barbettes were also 350 mm thick on the front and sides, but decreased to 250 mm on the rear. The main gun turrets had 350 mm faces, 250 mm sides, 305 mm rears, and 150 to 250 mm roofs. The secondary guns were protected with 170 mm of armor plate.

Machinery and other characteristics
The ships were to have been powered by either 2 or 4 sets of steam turbines driving 4 shafts. The steam plant consisted of 6 oil-fired and 16 coal-fired boilers trunked into a single funnel. Bunkerage was 2950 MT of coal and 1970 MT of fuel oil. The ships were intended to have a single tripod foremast, as was typical for German battleships of the period. Externally, the ships were very similar to the s.