Haruna fought in almost every major naval action of the Pacific Theater during World War II. She covered landings in Malaya and the Dutch East Indies in 1942 before engaging American forces at the Battle of Midway and during the Guadalcanal Campaign.

Throughout 1943, Haruna primarily remained at Truk Lagoon, Kure Naval Base, Sasebo Naval Base and the Lingga Islands. Haruna deployed on several occasions in response to American carrier airstrikes on Japanese island bases, participating in the Battle of the Philippine Sea and the Battle of Leyte Gulf in 1944, engaging American vessels at the Battle off Samar.

Transferred to Kure Naval Base in 1945, Haruna was was sunk by aircraft of Task Force 38 on 28 July 1945.
 

Second reconstruction, August 1933
No longer encumbered by the former Washington and London Treaty restrictions, Haruna was reconstructed into a fast battleship, capable of escorting Japanese fleet carriers. Her stern is lengthened and her bridge is rebuilt pagoda style. All boilers are are removed and replaced with eight oil-fired boilers and she receives new geared turbines. Her speed is increased to more than 30 knots.
Kongo's main belt was strengthened to a uniform thickness of eight inches and diagonal bulkheads of depths ranging from 5 to 8 inches were added to reinforce the main armored belt. The turret armor was strengthened to 10 inches, while 4 inches were added to portions of the deck armor. The ammunition magazine protection was also strengthened to 4.0 inches

War Service
November 29, 1941,
Accompanied by sister ship Kongo, Haruna departed the Hashirajima fleet anchorage as part of the Southern (Malay) Force's Main Body, under the overall command of Vice-Admiral Nobutake Kondo. Arriving on December 4, 1941, off the coast of southern Thailand and northern Malaya in preparation for the invasion of Thailand and the Malay Peninsula

December 9, 1941
The hunt and destruction of British Force Z
The Main Body, southeast of Indochina near Poulo Condore Island sorties south for a night attack against Force Z centered around Prince of Wales and Repulse, but no contact is made. December 10th, joined by Cruisers and Destroyers, the Main Body begins the search for the british fleet off Malaysia. Upon recieveing news that both battleships have been sunk, the Japanese forces withdrew tp Camranh Bay in French Indochina.
In January 1942, Haruna participated in most of the Japanese naval operations throughout the Southwest Pacific, covering further invasions of malaysia, Luzon at the Lingayan Gulf.
In late February 1942, Haruna was joined by sister ship Kongo, four fast aircraft carriers, five heavy cruisers and support ships in preparation for "Operation J", Japan's invasion of the Dutch East Indies. On 25 February, the Third Battleship Division provided cover for air attacks on the Island of Java. On 7 March 1942 The Haruna bombarded Christmas Island off the western coast of Australia before returning to Staring-baai for rest and maintenance

April 1942,
Haruna joined five fleet carriers in attacks on Colombo and Trincomalee on Ceylon. Following the destruction of the British heavy cruisers HMS Dorsetshire and HMS Cornwall, and the carrier HMS Hermes on April 5, 1942, this naval task force moved southwest to locate the remainder of the British Eastern Fleet, then under the command of Admiral James Somerville. On April 9, one of Haruna's reconnaissance seaplanes spotted the HMS Hermes south of Trincomalee. Having crippled the offensive capability of Britain's Eastern Fleet, the Third Battleship Division returned to Japan. Haruna was then drydocked throughout May 1942 for general repairs and refits

May 1942,
Haruna joined Kirishima as part of Vice-Admiral Chuichi Nagumo's carrier strike force during the Battle of Midway. During the battle she was attacked several times, shooting down 5 American aircraft and on the 5th of June, she took on survivors from the four destroyed Japanese aircraft carriers before returning to Japan.

In September and October 1942 Haruna took part in the Solomons campaign, escorting troop transports and bombarding Henderson Field
During the Battle of the Santa Cruz Islands on 26 October 1942, Haruna was attacked by a PBY Catalina flying boat but received no damage. In mid-November, Haruna provided distant cover for the failed efforts to bombard Henderson Field again and land reinforcements on Guadalcanal. On 15 November 1942, following the Japanese defeat and loss of Hiei and Kirishima during the Naval Battle of Guadalcanal, Haruna returned to Truk, where it remained for the rest of 1942

In spite of leaving on several sorties, Haruna saw no combat action during 1943.

In January 1944, Haruna was stationed at Kure. The Third Battleship Division departed Kure on March 8th, arriving at Lingga Roads on 14 Marchwhere they remained for training until 11 May 1944.
On May 11th, Haruna and Admiral Ozawa's Mobile Fleet departed Lingga for Tawi-Tawi, where they were joined by Vice-Admiral Takeo Kurita's "Force C". On June13th, Ozawa's Mobile Fleet departed Tawitawi for the Mariana Islands. During the Battle of the Philippine Sea, Haruna escorted Japanese fast carriers, and on June 20th. was hit by two 500 lb armor piercing bombs from U.S. carrier aircraft.On June 24th, she was drydocked in Kure for repairs and refitting. In August 1944 she transferred to Lingga Roads
In October 1944, Haruna departed Lingga in preparation for "Operation Sho-1", Japan's counterattack during the Battle of Leyte Gulf. On October 24th, Haruna was lightly damaged by fragments from near misses by American carrier aircraft in the Battle of the Sibuyan Sea. On October 25th, during the Battle off Samar, Haruna—as part of Admiral Kurita's Centre Force—engaged escort carriers and destroyers of the U.S. 7th Fleet's "Taffy 3". After a fierce defensive action by the American ships, Admiral Kurita elected to withdraw, ending the battle.