Question: Oscarsborg Fortress is best known for sinking the  German heavy cruiser named for the Prussian victor of what?
Context: Blücher was the second of five "Admiral Hipper"-class heavy cruisers of Nazi Germany's "Kriegsmarine", built after the rise of the Nazi Party and the repudiation of the Treaty of Versailles.  Named for Gebhard Leberecht von Blücher, the Prussian victor of the Battle of Waterloo, the ship was laid down in August 1936 and launched in June 1937.  She was completed in September 1939, shortly after the outbreak of World War II.  After completing a series of sea trials and training exercises, the ship was pronounced ready for service with the fleet on 5 April 1940. Operation Nordseetour was the first Atlantic sortie of the German heavy cruiser "Admiral Hipper" during December, 1940. USS "Northampton" (CL/CA-26) was the lead "Northampton"-class cruiser in service with the United States Navy.  She was commissioned in 1930, originally classified a light cruiser because of her thin armor but later reclassified a heavy cruiser because of her 8-inch guns.  During World War II she served in the Pacific and was sunk by Japanese torpedoes during the Battle of Tassafaronga on 30 November 1942.  She was named after the city of Northampton, Massachusetts, the home of former President Calvin Coolidge. Oscarsborg Fortress (Norwegian: Oscarsborg festning ) is a coastal fortress in the Oslofjord, close to the small town of Drøbak.  The best known part is situated on two small islets.  The main artillery batteries are on the island Håøya and smaller batteries on the mainland to the west and east in the fjord and was military territory until 2003 when it was made a publicly available resort island.  The fortress is best known for sinking the German heavy cruiser "Blücher" on 9 April 1940.  In 2014, Oscarsborg Fortress was given protected status, effective from 9 April that year. Émile Bertin was a French fast light cruiser named after Louis-Émile Bertin, a 19th-century naval architect.  She was designed to operate both as a minelayer and as a destroyer flotilla leader.  The design was the basis for later light and heavy French cruisers, particularly the slightly larger "La Galissonnière" class of cruisers.  This was the first French warship to use triple mountings. Operation "Rheinübung" ("Exercise Rhine") was the sortie into the Atlantic by the new German battleship "Bismarck" and heavy cruiser "Prinz Eugen" on 18–27 May 1941, during World War II.  This operation to block Allied shipping to the United Kingdom culminated with the sinking of "Bismarck". USS "Birmingham" (CL-62), a "Cleveland"-class light cruiser named for the city of Birmingham, Alabama, the "Steel City", was laid down at the Newport News Shipbuilding and Dry Dock Company of Newport News, Virginia on 17 February 1941 and launched on 20 March 1942 by Mrs. Cooper Green, wife of the president of the Birmingham City Commission.  She was commissioned on 29 January 1943, Captain John Wilkes in command.  "Birmingham" was one of the "fightingest" ships of the Navy and suffered heavy damage on at least three occasions. The Action of 8 June 1945, sometimes called the Sinking of "Ashigara" was a naval action that resulted in the sinking of the heavy cruiser "Ashigara" of the Imperial Japanese Navy by the British Royal Navy submarine HMS "Trenchant" .  "Ashigara"—which was being escorted by the destroyer "Kamikaze" —was being used to transport troops from Indonesia for the defence of Singapore and the sinking resulted in a huge loss of life. HMS "Cornwall", pennant number 56, was a County-class heavy cruiser of the "Kent" sub-class built for the Royal Navy in the mid-1920s.  The ship spent most of her pre-World War II career assigned to the China Station.  Shortly after the war began in August 1939, she was assigned to search for German commerce raiders in the Indian Ocean.  "Cornwall" was transferred to the South Atlantic in late 1939 where she escorted convoys before returning to the Indian Ocean in 1941.  She then sank the German auxiliary cruiser "Pinguin" in May.  After the start of the Pacific War in December 1941, she began escorting convoys until she was transferred to the Eastern Fleet in March 1942.  The ship was sunk on 5 April by dive bombers from three Japanese aircraft carriers during the Indian Ocean Raid. San Demetrio London is a 1943 British World War II docudrama based on the true story of the 1940 salvage of the tanker MV "San Demetrio" by some of her own crew, who reboarded her after she had been set on fire by the German heavy cruiser "Admiral Scheer" and then abandoned, during the Battle of the Atlantic.  The film was produced by Michael Balcon for Ealing Studios and directed by Charles Frend.
Answer: the Battle of Waterloo