Immediately after the Japanese attack on Pearl Harbor, the Navy reassigned the three battleships to the Pacific Fleet to shore up the fleet's battleship strength.
After arriving in California in January 1942, the ships spent the next several months patrolling the west coast of the United States and escorting convoys in the area.
They took part in the Aleutian Islands campaign between May and July 1943, with Idaho serving as the flagship of the bombardment group that shelled the islands of Attu and Kiska.
After maintenance and training at Pearl Harbor, the three New Mexicos then took part in the Gilbert and Marshall Islands campaign that began in November, where they provided naval gunfire support to the Marines who stormed ashore at Tarawa, Kwajalein, and Eniwetok, among other islands in the archipelago.
These operations continued into January 1944, at which point the fleet began preparations for the next major campaign, which would be directed against the Marianas Islands in the central Pacific.

New Mexico and Idaho took part in the Mariana and Palau Islands campaign beginning in June 1944, though Mississippi was out of service for a refit during the first part of the campaign.
They shelled Japanese positions on Saipan, Tinian, and Guam as amphibious forces assaulted each island in turn.
The two battleships remained with the invasion fleet to cover it from Japanese attacks while the Fast Carrier Task Force met and decisively defeated the Japanese 1st Air Fleet in the Battle of the Philippine Sea.
By September, Mississippi had returned to the fleet to relieve New Mexico for her own refit, and she and Idaho shelled the island of Pelelieu, the last battle of the Marianas campaign.
The fleet thereafter withdrew to Manus Island to prepare for the coming invasion of the Philippines, while New Mexico departed for a refit at the Puget Sound Navy Yard.

Mississippi supported the invasion of Leyte in October as part of the bombardment group under Rear Admiral Jesse B. Oldendorf.
The American invasion triggered the Japanese to launch Operation Shō-Gō 1, a major naval counterattack that resulted in the Battle of Leyte Gulf on 23–26 October, a complex battle that involved four separate actions.
She was present at the Battle of Surigao Strait on the night of 24 October, which was one component of the battle.
There, the Allied fleet destroyed the Japanese Southern Force consisting of a pair of old battleships, one heavy cruiser, and four destroyers; only one Japanese destroyer escaped the overwhelming Allied fleet.
Mississippi, which still had her old Mark 3 radars, had difficulty in finding a target in the darkness and fired only one salvo in the last battleship action in history.

By January 1945, New Mexico had rejoined the fleet, the next target of which was the invasion of Lingayen Gulf on the island of Luzon; she and Mississippi supported the amphibious assault and during the battle both ships were struck by a kamikaze suicide plane.
The two ships nevertheless remained in action until February when they departed for Pearl Harbor for repairs.
By that time, Idaho had completed her refit and had rejoined the fleet in time to take part in the Battle of Iwo Jima.
She shelled the island extensively before the Marines went ashore and continued to provide fire support during the battle.
Repairs to New Mexico and Mississippi were completed quickly, and all three sister ships were reunited to support the invasion of Okinawa in May 1945.
As Japan's military situation continued to deteriorate, they launched increasingly desperate kamikaze attacks.
New Mexico and Mississippi were both hit by another kamikaze and Idaho was damaged by a near miss.
New Mexico was also hit by a bomb, forcing her to withdraw for repairs.
All three ships were repaired in time to participate in the initial occupation of Japan in August and September.
Immediately after the Japanese attack on Pearl Harbor, the Navy reassigned the three battleships to the Pacific Fleet to shore up the fleet's battleship strength. After arriving in California in January 1942, the ships spent the next several months patrolling the west coast of the United States and escorting convoys in the area. They took part in the Aleutian Islands campaign between May and July 1943, with Idaho serving as the flagship of the bombardment group that shelled the islands of Attu and Kiska. After maintenance and training at Pearl Harbor, the three New Mexicos then took part in the Gilbert and Marshall Islands campaign that began in November, where they provided naval gunfire support to the Marines who stormed ashore at Tarawa, Kwajalein, and Eniwetok, among other islands in the archipelago. These operations continued into January 1944, at which point the fleet began preparations for the next major campaign, which would be directed against the Marianas Islands in the central Pacific.
New Mexico and Idaho took part in the Mariana and Palau Islands campaign beginning in June 1944, though Mississippi was out of service for a refit during the first part of the campaign. They shelled Japanese positions on Saipan, Tinian, and Guam as amphibious forces assaulted each island in turn. The two battleships remained with the invasion fleet to cover it from Japanese attacks while the Fast Carrier Task Force met and decisively defeated the Japanese 1st Air Fleet in the Battle of the Philippine Sea. By September, Mississippi had returned to the fleet to relieve New Mexico for her own refit, and she and Idaho shelled the island of Pelelieu, the last battle of the Marianas campaign. The fleet thereafter withdrew to Manus Island to prepare for the coming invasion of the Philippines, while New Mexico departed for a refit at the Puget Sound Navy Yard.
Mississippi supported the invasion of Leyte in October as part of the bombardment group under Rear Admiral Jesse B. Oldendorf. The American invasion triggered the Japanese to launch Operation Shō-Gō 1, a major naval counterattack that resulted in the Battle of Leyte Gulf on 23–26 October, a complex battle that involved four separate actions. She was present at the Battle of Surigao Strait on the night of 24 October, which was one component of the battle. There, the Allied fleet destroyed the Japanese Southern Force consisting of a pair of old battleships, one heavy cruiser, and four destroyers; only one Japanese destroyer escaped the overwhelming Allied fleet. Mississippi, which still had her old Mark 3 radars, had difficulty in finding a target in the darkness and fired only one salvo in the last battleship action in history.
By January 1945, New Mexico had rejoined the fleet, the next target of which was the invasion of Lingayen Gulf on the island of Luzon; she and Mississippi supported the amphibious assault and during the battle both ships were struck by a kamikaze suicide plane. The two ships nevertheless remained in action until February when they departed for Pearl Harbor for repairs. By that time, Idaho had completed her refit and had rejoined the fleet in time to take part in the Battle of Iwo Jima. She shelled the island extensively before the Marines went ashore and continued to provide fire support during the battle. Repairs to New Mexico and Mississippi were completed quickly, and all three sister ships were reunited to support the invasion of Okinawa in May 1945. As Japan's military situation continued to deteriorate, they launched increasingly desperate kamikaze attacks. New Mexico and Mississippi were both hit by another kamikaze and Idaho was damaged by a near miss. New Mexico was also hit by a bomb, forcing her to withdraw for repairs. All three ships were repaired in time to participate in the initial occupation of Japan in August and September.
New Mexico-class battleship