Question: Which U.S. Navy battleship was to be the second in its class but had its construction cancelled before the keel was laid?

Context paragraphs:
USS Kentucky (BB-66): USS "Kentucky" (BB-66) was an uncompleted battleship originally intended to be the second ship of the "Montana" class .  However, the U.S. Navy's experiences in World War II led it to conclude that rather than more battleships larger and more heavily armed than the "Iowa" class , it needed more fast battleships of that class to escort the new "Essex"-class aircraft carrier s being built.  As a result, hull BB-66 was reordered as an "Iowa"-class battleship midway through the war.

USS Tacoma (PGM-92): USS "Tacoma" (PG-92) was an "Asheville"-class gunboat of the U.S. Navy and the fourth ship to be named after the city of Tacoma, Washington.  "Tacoma" was the first in a series of revised "Asheville"-class gunboats.  Some sources call these revised boats "Tacoma"- or PG-92-class, but the U.S. Navy officially designates them as "Asheville"-class.  The keel of "Tacoma" was laid 24 July 1967 at the Tacoma Boatbuilding Co., in her namesake city.  She was launched on 13 April 1968, sponsored by Mrs. Arne K. Strom, and was commissioned on 14 July 1969, with Lt. Frank H. Thomas, Jr., in command.

Los Angeles-class submarine: The "Los Angeles" class is a class of nuclear-powered fast attack submarines (SSN) in service with the United States Navy.  The submarines are also known as the 688 class, after the hull number of lead vessel  .  They represent two generations and close to half a century of the U.S. Navy's attack submarine fleet.  As of 2017, 36 of the class are still in commission and 26 retired from service.  Of the 26 retired boats, 14 of them were laid up half way (approximately 17–18 years) through their projected lifespans due to their midlife reactor refuelings being cancelled.  A further four boats were proposed by the Navy, but later cancelled.  The class has more operating nuclear submarines than any other in the world.  All submarines of this class are named after American towns and cities (e.g., Key West, Florida, and Greeneville, Tennessee), the exception being USS "Hyman G. Rickover" .  This system of naming broke a long-standing tradition in the U.S. Navy of naming attack submarines for creatures of the ocean (e.g., USS "Nautilus" ).

South Dakota-class battleship (1920): The first "South Dakota" class was a class of six American battleships that were laid down in 1920 but never completed.  They would have been the last dreadnoughts in the Naval Act of 1916 to be commissioned had the Washington Naval Treaty not caused their cancellation one-third of the way through their construction.  They would have been the largest, most heavily armed and armored battleships in the U.S. Navy and, designed to achieve 23 kn , represented an attempt to abandon its 21 kn standardized fleet speed and catch up with the increasing fleet speeds of its main rivals, the British Royal Navy and Imperial Japanese Navy.  In this, size and secondary armament, they represented a break from the Standard-type battleship that had dominated American capital ship design for the prior five ship classes, while their use of standardized bridges, lattice masts and other features was a continuation of this practice and the increase in the number of main guns from the preceding "Colorado" class had long been standard U.S. naval policy.  The main restriction to which they had to adhere was the ability to pass through the Panama Canal.

USS William H. Bates (SSN-680): USS "William H. Bates" (SSN-680), a "Sturgeon"-class attack submarine, was planned to be the second U.S. Navy ship to be named USS "Redfish"—for the redfish, a variety of salmon also called blueback, sawqui, red salmon, and nerka—when the contract to build her was awarded to Ingalls Shipbuilding in Pascagoula, Mississippi, on 25 June 1968.  However, upon the 22 June 1969 death of William H. Bates (1917–1969), the U.S. Representative from Massachusetts's 6th Congressional District (1950–1969) known for his staunch support of nuclear propulsion in the U.S. Navy, she was renamed "William H. Bates" and was laid down on 4 August 1969 as the only ship of the U.S. Navy to have borne the name.  The reason for her naming by then-Secretary of the Navy John Chafee, breaking with a long-standing Navy tradition of naming U.S. Navy attack submarines for sea creatures, was best summed up by Admiral Hyman Rickover, the then-director of the Navy's nuclear reactors program, with the pithy comment that, "Fish don't vote!"

French battleship Danton: Danton was a semi-dreadnought battleship of the French Navy and the lead ship of her class.  She was a technological leap in battleship development for the French Navy, as she was the first ship in the fleet with turbine engines. However, like all battleships of her type, she was completed after the Royal Navy battleship HMS "Dreadnought" , and as such she was outclassed before she was even commissioned.

Montana-class battleship: The "Montana"-class battleships of the United States Navy were planned as successors to the "Iowa" class , being slower but larger, better armored, and having superior firepower.  Five were approved for construction during World War II, but changes in wartime building priorities resulted in their cancellation in favor of the "Essex"-class aircraft carrier and "Iowa" class before any "Montana"-class keels were laid.

Deutschland-class battleship: The "Deutschland" class was a group of five pre-dreadnought battleships built for the German Kaiserliche Marine.  The class comprised "Deutschland" , "Hannover" , "Pommern" , "Schlesien" , and "Schleswig-Holstein" .  Built between 1903 and 1908, the ships closely resembled those of the preceding "Braunschweig" class , though they had stronger armor protection.  They were made obsolete before they were even completed by the launch of the revolutionary Royal Navy battleship HMS "Dreadnought" in 1906.  As a result, they were the last ships of that type built for the German Navy.  They were followed by the "Nassau"-class battleship s, Germany's first dreadnought battleships.

USS Illinois (BB-7): USS "Illinois" (BB-7) was a pre-dreadnought battleship built for the United States Navy.  She was the lead ship of the "Illinois" class , and was the second ship of the U.S. Navy to be named for the 21st state.  Her keel was laid in February 1897 at the Newport News Shipbuilding & Dry Dock Company, and she was launched in October 1898.  She was commissioned in September 1901.  The ship was armed with a main battery of four 13 in guns and she had a top speed of 16 kn .

D-class cruiser (Germany): The D-class cruisers were a pair of cruisers, classified as "Panzerschiffe" ("armored ships") by the Kriegsmarine.  The ships were improved versions of the preceding "Deutschland"-class cruiser s, authorized by Adolf Hitler in 1933.  They were intended to counter a new French naval construction program.  Displacement increased to 20000 LT , but Hitler allowed only increases to armor, prohibiting additions to the ships' main battery.  Only one of the two ships was laid down, but it was canceled less than five months after the keel was laid.  It was determined that the designs should be enlarged to counter the new French "Dunkerque"-class ships.  The construction contracts for both ships were superseded by the "Scharnhorst"-class battleship s.

Supporting paragraphs: USS Kentucky (BB-66) Montana-class battleship
Answer: USS "Kentucky"