The Scharnhorst-class was a class of battleships or battlecruisers, depending on one's definition, produced by Nazi Germany during the 1930s immediately before WWII. They were meant to serve as a counter to the French Dunkerque-class which was being be built around that time. Built to fight in the North Sea, their armament was limited by the political need not to anger Britain or France. The Treaty of Versailles in 1919 banned Germany from building new battleships, but allowed "armored vessels". However, the Anglo-German Naval Agreement (AGNA) allowed Germany 35% of the total tonnage of the Royal Navy, and new battleships or battlecruisers. This agreement would pave the way for the construction of the Bismarck-class and the H-class.
Three days before the signing of the AGNA on 15 June 1935, the keel of the Scharnhorst was laid down in Wilhelmshaven. One month before the keel for the Gneisenau was laid down in Kiel on 16 May. The designs for these ships had been completed long before, with an armament of 9 28cm/54.5 SK C/34 guns in three triple turrets (one the few German ship classes to be equipped with tripe turrets) being selected. Armor consisted of a vertical 350mm belt tapering off to 170mm at the outboard slope of the armor deck, and deck armor ranging from 50mm to 105mm. The secondary armament consisted of 12 15cm/55 SK C/28 guns mounted in 4 twin and 4 single turrets (these are not be confused with the 150mm AA guns the Scharnhorst-class carried). The armor on the 28cm turrets was 360mm on the face, 200mm on the sides, 150mm on the roof, and a range of 350mm to 200mm on the barbettes*. Displacement was 37,100 tons. One interesting point about their armor is that generally on battleships, the armor corresponded to the main battery (e.g. guns of 406mm, armor of a thickness that would defeat a 406mm shell). This was not the case with the Scharnhorst-class which carried far more than necessary to defeat an 283mm shell.
The Scharnhorst and Gneisenau were considered by the Kriegsmarine to be battleships, but were viewed by the Royal Navy as battlecruisers. Their armor listed above compares very favorably to Britain largest battlecruiser, the HMS Hood. The Hood had a 305mm belt (the belt on the Hood was angled at 12 degrees, whereas the Scharnhorst-class had vertical belts), which tapered off to 127mm and 152mm at the ends of the ship. Turret armor on the Hood was slightly heavier than the Scharnhorst-class, the face of the Hood's turrets was 373mm, 299 to 274mm on the sides, and 124mm on the roof.
The Scharnhorst and Gneisenau were built for combat in the North Sea against French battleships which is why they carried battlecruiser thickness armor. The 28cm guns were selected for their high rate of fire and the fact that the Dunkerque-class was thought to mostly lightly armored. However, when faced with vessels with a greater armament and armor the Scharnhorst and Gneisenau were unable to return any meaningful damage.
The operational history is the Scharnhorst-class is excellent with both ships serving well throughout their service lives. During the Invasion of Norway the Scharnhorst and Gneisenau sank the carrier HMS Glorious and two escorting destroyers. During this engagement the Scharnhorst was hit by one torpedo launched by one escorting destroyers which did serious damage to propulsion and flooded four watertight compartments. From the sinking of the Glorious for about six month the Scharnhorst and Gneisenau were inactive while the Scharnhorst underwent repairs. In January of 1941 both ships sortied from Kiel to attack British convoys. They escaped detection and came upon the convoy HX 106 which was escorted by the HMS Ramilles, causing the Scharnhorst and Gneisenau to break off their attack. The ships returned to Brest where, after undergoing repairs, participated in the infamous Channel Dash in February 1941. Both the Scharnhorst and Gneisenau sustained mine damage off Holland during the Channel Dash and were forced to undergo repairs in Kiel. From February 1941 to March 1941 the Scharnhorst and Gneisenau would remain in German waters. In March 1943 the Scharnhorst was deployed to Norway where she was to link up with the Tirpitz and attack convoys sailing to Russia. The Gneisenau was also supposed to sail with her, but took heavy bomb damage from RAF bombers in late February 1942, and was slated to be reconstructed. This reconstruction would have included an upgrade to her armament with 6 380mm guns similar to those carried on the Bismarck-class. From here the ships separated.
The Scharnhorst arrived in Norway on March 22nd. From April 1943 to September 1943 the Scharnhorst and Tirpitz were inactive due to a fuel shortage. Then on September 8th the Scharnhorst and Tirpitz sortied to Spitzbergen where they bombarded shore installations. On December 22nd the Scharnhorst sortied for her final mission (the Tirpitz did not sail with her because she had been damaged by British midget submarines soon after the Spitzbergen operation) to attack convoy JW 55B.
Convoy JW 55B was escorted by three British cruisers, the light cruisers Sheffield and Belfast as well as the heavy cruiser Norfolk (these were known as Force 1). The King George V-class battleship Duke of York was also in the area providing overwatch for JW 55B and another convoy, RA 55A. The Scharnhorst was unable to make contact with JW 55B, but did find the three escorting cruisers. Force 1 detected the Scharnhorst at a range of 33,000 meters from Force 1, 60,000 meters from the convoy. The Scharnhorst was unaware of the British presence since her radar was off to avoid detection. The British opened fire at a range of 8,600 with star shells to illuminate the Scharnhorst at 0840 on December 26th. During this encounter (from 0925 to 0955) the Scharnhorst sustained two 203mm hits, one of which destroyed the forward rangefinders and crippled the Scharhorst's radar capability (the shell sheared off the radar antenna and killed all personnel in the radar receiving room). The Scharnhorst was now blind in the forward sector, as the aft radar had a limited sweep over the forward sector. At 0955 the Scharnhorst was able to break away from Force 1 and escape.
"The sinking of Scharnhorst"
At 1200 the Belfast was able to reestablish radar contact with the Scharnhorst. From this point till about 1315 the Scharnhorst fought with Force 1, scoring a serious hit on the Norfolk around 1223. Around 1315 broke contact and made for Norway. However, in making for Norway the Scharnhorst had to cross the course of the Duke of York. At 1617 the Duke of York made radar contact with the Scharnhorst at a range of 42,500 meters. At 1650 the Duke of York opened fire on the Scharnhorst after she had been illuminated by star shells from the Belfast.
Map of the Battle of North Cape (click to enlarge)
This began the last surface engagement of German and British capital ships of WWII. The duel that began was highly unequal because the Scharnhorst 283mm guns simply could not penetrate the Duke of York's armor at any point. The Scharnhorst was able to damage the Duke of York's superstructure, and temporarily knock out her fire control radar. However, between 1650 and 1842, when the Duke of York ceased firing, the Scharnhorst took at least 13 356mm hits. At the end of the gunnery duel the Scharnhorst was still making around 22 knots, leading to a British torpedo attack around 1850. 4 torpedoes hit, slowing the Scharnhorst to 12 knots, though the chief engineer reported he could still produce 22 knots. At this point a second torpedo attack was made because of the apparent inability to sink German capital ships by gunfire (this was learned from inability to sink the Bismarck by gunfire). At 1900 all confidential papers were burned by order of the Scharnhorst's captain. At 1945 the Scharnhorst sank bow first with her propellers still turning. Out of a crew of 1968 officers and enlisted man, only 36 enlisted men survived the engagement. Thus, ended the Battle of North Cape.
As to the fate of the Gneisenau, work was eventually stopped in early 1943 at the order of Hitler, who was angry at the failure of German surface raiders. The 283mm turrets that had been removed to make way for the new 380mm turrets, were shipped to Norway. There they were installed as coastal defense guns, where one remains there to this day. From 1943 to till 1945 nothing happened to the remains of the Gneisenau. In March 1945 the Gneisenau was towed into the entrance of the harbor of Gotenahfen where she was sunk as a block ship to delay the Advance of the Red Army. Her hull was scraped by the Polish government from 1947 to 1951.
The Scharnhorst-class was never able to fulfill it's mission of fighting in the French or British in the North Sea. They were forced into a commerce raiding role which they were not optimized for, and when faced with superior opponents were unable to deal damage back. Their armor was excellent for their displacement, but they did not have the survivability of German WWI battlecruisers. Germany packed a lot of punch into relatively small hulls, an they would have performed well in a hypothetical North Sea engagement. However, when forced into a commerce raiding role or engaging more heavily armored ships, they simply could not do the job.
* All turret armor numbers are taken from Naval Weapons of World War Two by John Campbell.