[2] The Nagara-class vessels were essentially identical to the previous Kuma-class cruisers, retaining the same hull design, engines and main weaponry, with the addition of the new 610 mm Type 93 Long Lance Torpedoes, which required a larger launcher.
Even so, the arrangement proved unwieldy, and the catapult was moved to the rear of each ship in the class, between the No.5 and No.6 gun mounts during retrofits in 1929-1934.
At the time of the attack on Pearl Harbor, Isuzu was participating in the invasion of Hong Kong, as part of the 15th Escort Squadron in Vice Admiral Kiyoshi Hara's Second China Expeditionary Fleet.
Isuzu remained based in Hong Kong after its capture by Japan from the end of December 1941 to April 1942, returning briefly to her home port of Mako, in the Pescadores to escort reinforcements for the Japanese 25th Army to Singora, Thailand and Camranh Bay, French Indochina[5] The 15th Escort Squadron was deactivated on 10 April 1942 and Isuzu was reassigned to Rear Admiral Kenzaburo Hara's CruDiv 16 under Vice Admiral Ibō Takahashi's 2nd Southern Expeditionary Fleet.
She was joined by the Natori and Kinu and was assigned a patrol area in the Dutch East Indies extending from Makassar, Celebes to Balikpapan, Borneo and Surabaya, Java, becoming flagship of CruDiv 16 from 1 May 1942.
From Shortland, Isuzu was ordered on to Truk, in the Caroline Islands, where it replaced the damaged Jintsu as flagship of Rear Admiral Raizo Tanaka's DesRon 2's DesDivs 15, 24 and 31 (9 destroyers).
Isuzu provided cover with DesDivs 15 and 31 and also fired on Marine batteries on Tulagi Island during the Bombardment of Henderson Field, Guadalcanal by the Kongō and Haruna.
On 1 April 1943, with repairs and modification yet incomplete, Isuzu was assigned to Rear Admiral Kenzo Ito's new CruDiv 14 with Naka.
Isuzu continued to be based out of Truk to 15 October 1943, when it was recalled to Tokushima and (together with Naka) reassigned to ferry troops to Shanghai.
However, the planes from Task Force 38's aircraft carriers USS Saratoga and Princeton did little more than strafe Isuzu, which later returned to Truk for repairs.
While at Roi, on 5 December 1943, Isuzu was attacked by Douglas SBD Dauntless dive bombers and Grumman TBF Avenger torpedo-bombers from TG 50.1's aircraft carriers USS Yorktown and Lexington.
On 20 October 1944, Isuzu participated in the Battle of Leyte Gulf as part of Vice Admiral Jisaburō Ozawa's Northern Mobile ("Decoy") Force.
[5] Isuzu returned to Okinawa on 27 October 1944, and from there to Kure, where she was assigned to make a troop transport run to Manila and Brunei.
On 19 November 1944, 55 miles (89 km) west of Corregidor, Isuzu was attacked by USS Hake and hit by one of six torpedoes fired, with severe damage to its stern and destroying her rudder.
She was spotted by a wolf pack with the submarines USS Charr, Besugo and Gabilan, which was joined by HMS Spark.
18 (Netherlands East Indies) Squadron RAAF, based at Batchelor Airfield south of Darwin, Australia.
The following day, 7 April 1945, 60 nautical miles (111 km; 69 mi) northwest of Bima, Isuzu was struck by one of five torpedoes fired by USS Gabilan.
While her crew was performing emergency repairs, USS Charr fired four torpedoes, hitting Isuzu portside twice near the aft engine room.
On the same day, just a few hours apart, the battleship Yamato and her escorts were sunk by US aircraft in an attempted suicide attack on Okinawa.