Nagato, named for Nagato Province, was ordered on 12 May 1916 and laid down at the Kure Naval Arsenal on 28 August 1917 as the lead ship of her class.
She was launched on 9 November 1919 by Admiral Katō Tomosaburō, completed on 15 November 1920 and commissioned 10 days later with Captain Nobutaro Iida in command.
Nagato was assigned to the 1st Battleship Division and became the flagship of Rear Admiral Sōjirō Tochinai.
On 13 February 1921, the ship was inspected by the Crown Prince, Hirohito.
Captain Kanari Kabayama relieved Iida on 1 December 1921.
The ship hosted Marshal Joseph Joffre on 18 February 1922 and Edward, Prince of Wales, and his aide-de-camp Lieutenant Louis Mountbatten on 12 April during the prince's visit to Japan.

After the 1923 Great Kantō earthquake, Nagato loaded supplies from Kyushu for the victims on 4 September.
Together with her sister ship Mutsu, she sank the hulk of the obsolete battleship Satsuma on 7 September 1924 during gunnery practice in Tokyo Bay in accordance with the Washington Naval Treaty.
The ship was transferred to the reserve of the 1st Division on 1 December and became a gunnery training ship.
In August 1925, aircraft handling and take-off tests were conducted aboard Nagato.
She was reassigned as the flagship of the Combined Fleet on 1 December, flying the flag of Admiral Keisuke Okada.
Captain Kiyoshi Hasegawa assumed command of the ship on 1 December 1926.

Nagato was again placed in reserve on 1 December 1931 and her anti-aircraft armament was upgraded the following year.
In August 1933 the ship participated in fleet maneuvers north of the Marshall Islands and she began her first modernization on 1 April 1934.
This was completed on 31 January 1936 and Nagato was assigned to the 1st Battleship Division of the 1st Fleet.
During the attempted coup d'état on 26 February by disgruntled Army officers, the ship was deployed in Tokyo Bay and some of her sailors were landed in support of the government.
In August, she transported 1,749 men of the 43rd Infantry Regiment of the 11th Infantry Division from Shikoku to Shanghai during the Second Sino-Japanese War.
Her floatplanes bombed targets in Shanghai on 24 August before she returned to Sasebo the following day.
Nagato became a training ship on 1 December until she again became the flagship of the Combined Fleet on 15 December 1938.
The ship participated in an Imperial Fleet Review on 11 October 1940.
She was refitted in early 1941 in preparation for war.
Nagato, named for Nagato Province, was ordered on 12 May 1916 and laid down at the Kure Naval Arsenal on 28 August 1917 as the lead ship of her class. She was launched on 9 November 1919 by Admiral Katō Tomosaburō, completed on 15 November 1920 and commissioned 10 days later with Captain Nobutaro Iida in command. Nagato was assigned to the 1st Battleship Division and became the flagship of Rear Admiral Sōjirō Tochinai. On 13 February 1921, the ship was inspected by the Crown Prince, Hirohito. Captain Kanari Kabayama relieved Iida on 1 December 1921. The ship hosted Marshal Joseph Joffre on 18 February 1922 and Edward, Prince of Wales, and his aide-de-camp Lieutenant Louis Mountbatten on 12 April during the prince's visit to Japan.
After the 1923 Great Kantō earthquake, Nagato loaded supplies from Kyushu for the victims on 4 September. Together with her sister ship Mutsu, she sank the hulk of the obsolete battleship Satsuma on 7 September 1924 during gunnery practice in Tokyo Bay in accordance with the Washington Naval Treaty. The ship was transferred to the reserve of the 1st Division on 1 December and became a gunnery training ship. In August 1925, aircraft handling and take-off tests were conducted aboard Nagato. She was reassigned as the flagship of the Combined Fleet on 1 December, flying the flag of Admiral Keisuke Okada. Captain Kiyoshi Hasegawa assumed command of the ship on 1 December 1926.
Nagato was again placed in reserve on 1 December 1931 and her anti-aircraft armament was upgraded the following year. In August 1933 the ship participated in fleet maneuvers north of the Marshall Islands and she began her first modernization on 1 April 1934. This was completed on 31 January 1936 and Nagato was assigned to the 1st Battleship Division of the 1st Fleet. During the attempted coup d'état on 26 February by disgruntled Army officers, the ship was deployed in Tokyo Bay and some of her sailors were landed in support of the government. In August, she transported 1,749 men of the 43rd Infantry Regiment of the 11th Infantry Division from Shikoku to Shanghai during the Second Sino-Japanese War. Her floatplanes bombed targets in Shanghai on 24 August before she returned to Sasebo the following day. Nagato became a training ship on 1 December until she again became the flagship of the Combined Fleet on 15 December 1938. The ship participated in an Imperial Fleet Review on 11 October 1940. She was refitted in early 1941 in preparation for war.
Japanese battleship Nagato