Atago (愛宕) was the second vessel in the Takao-class heavy cruisers, active in World War II with the Imperial Japanese Navy (IJN).

These were among the largest and most modern cruisers in the Japanese fleet, designed with the intention to form the backbone of a multipurpose long-range strike force.

[2] Propulsion was by 12 Kampon boilers driving four sets of single-impulse geared turbine engines, with four shafts turning three-bladed propellers.

[2] Atago's main battery was ten Type 3 20 cm naval guns, the heaviest armament of any heavy cruiser in the world at the time, mounted in five twin turrets.

[2] Atago was laid down at Kure Naval Arsenal on 28 April 1927, launched on 16 June 1930, and commissioned into the Imperial Japanese Navy on 30 March 1932.

From 11 August 1941, Atago was commanded by Captain Matsuji Ijuin, and on 29 November was made flagship of Vice Admiral Nobutake Kondō's Sentai-4, along with sister ships Maya, Chōkai, and Takao.

On 4 March, Atago, Takao and Maya, together with the destroyers Arashi and Nowaki, attacked a convoy which had departed Tjilatjap for Fremantle, Australia, and sank the Royal Australian Navy sloop HMAS Yarra after a 90-minute battle, along with the British tanker Francol, depot ship Anking, and British minesweeper 51.

After taking Vice Admiral Kondō on an inspection tour of Japan’s new possessions in the former Netherlands East Indies, Atago returned to Yokosuka Naval District on 17 April 1942, where she was assigned to the unsuccessful pursuit of Admiral William F. Halsey's Task Group 16.2 (TG 16.2) after the Doolittle Raid on Tokyo.

[4] Atago underwent a second modernization program at Yokosuka from 22 April to 21 May 1942 in which her single 12 cm/45 10th Year Type naval guns were replaced with new dual Type 89 12.7 cm (5 in) dual purpose guns, Atago departed for the Battle of Midway, where she was used to escort the transports ferrying the invasion force.

[6] Atago also played a very minor role in Battle of Santa Cruz Islands (26–27 October) [5] In the Second Naval Battle of Guadalcanal (15 November), during a night gun duel with the American battleships USS South Dakota and Washington, Atago and Takao hit South Dakota with seventeen 20 cm (8 in) rounds and one 12.7 cm (5.0 in).

[4] On 25 January 1943, Atago returned to Truk to continue Japanese efforts to hold the Solomon Islands, and eventually to support the evacuation of Guadalcanal.

Atago remained based out of Truk through July 1943, when she returned to Yokosuka Naval Arsenal for her third modernization and refit, which added two triple-mount Type 96 25 mm (0.98 in) anti-aircraft guns.

[4] On 23 August 1943, Atago returned to Truk with Army reinforcements for Rabaul, and continued making sorties supporting Japanese forces in the Solomon Islands through November.

In what came to be called the "Great Marianas Turkey Shoot", Japanese aircraft attacking US Task Force 58 off of Saipan suffered overwhelming losses.

Four torpedoes fired from the submarine USS Darter, skippered by Commander David H. McClintock, struck the Atago, setting her ablaze.