The sixth Delaware (BB-28) was launched on 6 February 1909 by the Newport News Shipbuilding Co., Newport News, Virginia, sponsored by Mrs. A.P. Cahall, niece of the Governor of Delaware, and commissioned on 4 April 1910 with Captain C.A. Gove in command.

After visiting Wilmington, Delaware, from 3 to 9 October 1910 to receive a gift of a silver service from the state, Delaware sailed from Hampton Roads on 1 November with the First Division, Atlantic Fleet. The ship visited Weymouth, England, and Cherbourg, France, and after battle practice at Guantanamo Bay, Cuba, returned to Norfolk on 18 January 1911. She departed on 31 January to carry the remains of Chilean Minister Cruz to Valparaíso, sailing via Rio de Janeiro, Brazil, and Punta Arenas, Chile. Returning to New York on 6 May, she sailed on 4 June for Portsmouth, England, where from 19 to 28 June she took part in the fleet review accompanying the coronation of King George V.

From 1912 to 1917, in operations with the Fleet, Delaware participated in exercises, drills, and torpedo practice at Rockport and Provincetown, Massachusetts. She engaged in special experimental firing and target practice at Lynnhaven Roads, trained in Cuban waters, and provided summer training for midshipmen. She passed before President Taft and the Secretary of the Navy in the Naval Review of 14 October 1912 and visited Villefranche, France, in 1913 with battleships Wyoming (BB-32) and Utah (BB-31). In 1914 and 1915, she cruised off Veracruz to protect American lives and property during the political disturbances in Mexico.

With the outbreak of World War I in Europe, Delaware returned from winter maneuvers in the Caribbean to train armed guard crews and engineers and to prepare the Fleet for war. On 25 November 1917, she sailed from Lynnhaven Roads with Division 9 for Scapa Flow, Scotland. After encountering bad weather in the North Atlantic, she joined the 6th Battle Squadron, British Grand Fleet, on 14 December for exercises.

On 6 February 1918, the 6th Battle Squadron escorted a group of merchant ships to Norway. Near Stavanger, Delaware evaded two submarine attacks. The squadron returned to Scapa Flow on 10 February. Delaware participated in two more convoy voyages in March and April, then sailed with the Grand Fleet on 24 April to reinforce the 2nd Battle Cruiser Squadron. The vessels of the advance screen made contact with the enemy, but no action ensued.

From 30 June to 2 July 1918, the 6th Battle Squadron screened American ships laying the North Sea mine barrage. On 22 July, George V inspected the ships of the Grand Fleet at Rosyth, Scotland. Delaware was relieved by Arkansas (BB-33) on 30 July and sailed for Hampton Roads, arriving on 12 August.

Delaware remained at York River until 12 November 1918, then sailed to Boston Navy Yard for an overhaul. On 11 March 1919, she rejoined the Fleet in Cuban waters for exercises. Returning to New York on 14 April, she continued to operate in division, squadron, and fleet maneuvers and participated in the Presidential Fleet Review at Hampton Roads on 28 April 1921. She made two midshipmen practice cruises, one to Colón, Martinique, and other ports in the Caribbean and to Halifax, Nova Scotia, between 6 June and 31 August 1922, and a second to Europe, visiting Copenhagen, Greenock, Cadiz, and Gibraltar between 9 July and 29 August 1923.

Delaware entered Norfolk Navy Yard on 30 August 1923, and her crew was transferred to Colorado (BB-45), a newly commissioned battleship. Moving to Boston Navy Yard in September, she was stripped of warlike equipment and decommissioned on 10 November 1923. Delaware was sold on 5 February 1924 and scrapped in accordance with the Washington Treaty on the limitation of armaments.