SMS Bayern was the lead ship of the Bayern class of dreadnought battleships in the German Kaiserliche Marine (Imperial Navy). The vessel was launched in February 1915 and entered service in July 1916, too late to take part in the Battle of Jutland. Her main armament consisted of eight 38 cm (15 in) guns in four turrets, which was a significant improvement over the preceding König's ten 30.5 cm (12 inch) guns. The ship was to have formed the nucleus for a fourth battle squadron in the High Seas Fleet, along with three of her sister ships. Of the other ships only one—Baden—was completed; the other two were canceled later in the war when production requirements shifted to U-boat construction.

Bayern was commissioned midway through the war, and had a limited service career. The first operation in which the ship took part was an abortive fleet advance into the North Sea on 18–19 August 1916, a month after she had been commissioned. The ship also participated in Operation Albion in the Gulf of Riga, but shortly after the German attack began on 12 October 1917, Bayern was mined and had to be withdrawn for repairs. She was interned with the majority of the High Seas Fleet at Scapa Flow in November 1918 following the end of World War I. On 21 June 1919, Admiral Ludwig von Reuter ordered the fleet to be scuttled; Bayern sank at 14:30. In September 1934, the ship was raised, towed to Rosyth, and scrapped.

Design work on the Bayern class began in 1910 in the context of the Anglo-German naval arms race, with initial discussions focused on the caliber of the main battery; previous German battleships had carried 30.5 cm (12 in) guns, but as foreign navies adopted 34 cm (13.5 in) and 35.6 cm (14 in) weapons, the German naval command felt the need to respond with larger guns of their own. They considered 32 cm (12.6 in), 38 cm (15 in), and 40 cm (15.7 in) guns. Admiral Alfred von Tirpitz, the State Secretary of the Reichsmarineamt (Imperial Naval Office), was able to use public outcry over the Agadir Crisis to pressure the Reichstag (Imperial Diet) into appropriating additional funds for the Kaiserliche Marine (Imperial Navy) to offset the additional cost of the larger weapons. The design staff settled on the 38 cm caliber since the 40 cm was significantly more expensive and the 38 cm gun marked a significant improvement over existing German guns.

Bayern was 179.4 m (588 ft 7 in) long at the waterline, and an even 180 m (590 ft 7 in) long overall. She had a beam of 30 m (98 ft 5 in) and a draft of 9.3–9.4 m (30 ft 6 in – 30 ft 10 in) Bayern displaced 28,530 metric tons (28,080 long tons) at a normal displacement; at full combat load, she displaced up to 32,200 t (31,700 long tons). Bayern was powered by three Parsons steam turbines, with steam provided by three oil-fired and eleven coal-fired Schulz-Thornycroft water-tube boilers. Her propulsion system was rated at 35,000 metric horsepower (35,000 shp) for a maximum speed of 21 knots (39 km/h; 24 mph), and on trials achieved 55,967 metric horsepower (55,201 shp) for a maximum speed of 22 knots (41 km/h; 25 mph). The ship could carry up to 3,400 t (3,300 long tons; 3,700 short tons) of coal and 620 t (610 long tons; 680 short tons) of fuel oil, which provided a maximum range of 5,000 nmi (9,300 km; 5,800 mi) at a cruising speed of 12 kn (22 km/h; 14 mph).

The ship was the first German warship armed with eight 38 cm (15 in) SK L/45 guns. The main battery guns were arranged in four twin gun turrets: two superfiring turrets each fore and aft. Her secondary armament consisted of sixteen 15 cm (5.9 in) SK L/45 guns, four 8.8 cm (3.5 in) SK L/45 guns and five 60 cm (23.6 in) underwater torpedo tubes, one in the bow and two on each beam. Upon commissioning, she carried a crew of 42 officers and 1,129 enlisted men. The ship had an armored belt that was 170–350 mm (6.7–13.8 in) thick and an armored deck that was 60–100 mm (2.4–3.9 in) thick. Her forward conning tower had 400 mm (15.7 in) sides, and the main battery turrets had 350 mm thick sides and 200 mm (7.9 in) thick roofs.

Bayern was ordered with the provisional name "T" in 1912, under the fourth and final Naval Law, which was passed that year. Work began at the Howaldtswerke Dockyard in Kiel under construction number 590. The ship was laid down on 22 December 1913 and launched on 18 February 1915. After fitting out, she was commissioned on 18 March 1916, but remained largely idle in port for the next month, undergoing initial tests, including inclination tests to determine how the vessel responded to flooding. She got underway on 15 April for initial trials of her main battery, which lasted into the next day. Bayern conducted her first full-power speed test on 25 April off the island of Alsen; these trials continued until 2 May. After further examinations, the ship was deemed ready for service on 15 July, a month and a half too late for her to participate in the Battle of Jutland.

Bayern joined III Battle Squadron of the High Seas Fleet upon her commissioning. The ship would have been available for the operation, but the ship's crew, composed largely of the crew from the recently decommissioned battleship Lothringen, was given leave. She had cost the Imperial German Government 49 million Goldmarks. Bayern was later joined in service by one sister ship, Baden. Two other ships of this class, Sachsen and Württemberg, were canceled before they were completed. At the time of her commissioning, Bayern's commander was Kapitän zur See (Captain at Sea) Max Hahn. Ernst Lindemann, who went on to command the battleship Bismarck during her only combat sortie in World War II, served aboard the ship as a wireless operator. On 25 May, Ludwig III of Bavaria, the last King of Bavaria, visited the ship. Bayern briefly served as the fleet flagship, from 7 to 16 August.

Admiral Reinhard Scheer planned a fleet advance for 18–19 August 1916; the operation consisted of a bombardment conducted by I Scouting Group. This was an attempt to draw out and destroy Admiral David Beatty's battlecruisers. As Moltke and Von der Tann were the only two German battlecruisers still in fighting condition, three dreadnoughts were assigned to the unit for the operation: Bayern and the two König-class ships Markgraf and Grosser Kurfürst. Admiral Scheer and the rest of the High Seas Fleet, including 15 dreadnoughts, were to trail behind and provide cover. The makeshift I Scouting Group conducted familiarization exercises on 15 August in preparation for the operation; Admiral Franz von Hipper was displeased by the slow speed of the battleships and Scheer ordered the unit not to exceed 20 nautical miles (37 km; 23 mi) from the main fleet so as to avoid being cut off by the faster British battlecruisers.