USS Idaho (BB 42)

USS Idaho (BB 42) was a New Mexico class battleship that was in the Atlantic when the Japanese attacked Pearl Harbor, and that was involved in most of the island invasions in the Pacific from 1943 until the end of the war, although not the invasion of the Philippines.

Normally the US Congress only authorised two battleships in each fiscal year (thus the series of two-ship battleship classes), but the New Mexico class contained three ships. Mississippi and New Mexico were funded by Congress, but the new USS Idaho (BB 42) was funded by selling two older battleships (USS Mississippi BB 23 and USS Idaho BB 24) to Greece. The Idaho was laid down in 1915, launched in 1917 and commissioned into the US Navy on 24 March 1919.

USS Idaho (BB-42) bombards Okinawa
USS Idaho (BB-42) bombards Okinawa

The New Mexico class ships were modernized in the early 1930s. Their machinery was replaced with new boilers and geared turbines. The cage masts were removed and two tower bridges built - a large one forward and smaller one aft. Anti-torpedo bulges were added and the gun elevation increased to 30 degrees.

During the war the Idaho was given a completely new secondary armament, consisting of ten modern 5in/38 guns in single gun houses, as used for the main armament of contemporary destroyers). She ended the war with ten quad mountings for 40mm guns and 43 Oerlikons.

The Idaho was normally part of the US Pacific Fleet, but like the other two members of the New Mexico class, in the summer of 1941 she was allocated to the Neutrality Patrol in the Atlantic, where they formed Task Force 1. From September she was based in Iceland, and she was at Reykjavik when the Japanese attacked Pearl Harbor. The three New Mexico class ships were ordered back to the Pacific, where they patrolled the US west coast, and escorted convoys to Hawaii.

Task Force 1 officially returned to Pearl Harbor in August 1942, but later in the year, with the threat to California and Hawaii receding, the Idaho sailed to Bremerton for repairs and a refit. She returned to the fleet in time to form part of Task Group 51.1 (Nevada, Pennsylvania and Idaho) for the invasion of the Aleutian Islands.

Men in 14in guns, USS Idaho (BB-42)
Men in 14in guns, USS Idaho (BB-42)

On 11 May 1943 the Idaho provided fire support for the invasion of Attu. She also supported the invasion of Kiska on 15 August, but the Japanese had evacuated the island in late July and there was no fighting. On 27 July the Idaho was involved in the 'battle of the pips' when she and the Mississippi fired 518 rounds of 14in shells at false radar contacts in near zero visibility. 

In November 1943 Idaho, New Mexico, Pennsylvania and Mississippi formed the Northern Attack Group (TG 52.2) under Rear Admiral Griffin, taking part in the invasion of Makin in the Gilbert Islands (Operation Galvanic). The Idaho arrived off Makin on 20 November and remained there until 5 December.

In January-February 1944 the same four battleships under the same commander formed the Southern Attack Force (FSG 52.8) during Operation Flintlock, the invasion of the Marshall Islands. The Idaho bombarded Kwajalein from 31 January to 5 February, before moving on to take part in a diversionary bombardment of Kavieng on New Ireland on 20 March (while MacArthur invaded Emirau Island in the Bismarck Archipelago). 

Bake Shop on USS Idaho (BB-42), 1919
Bake Shop on USS Idaho (BB-42), 1919

Next came Operation Forager, the invasion of the Mariana Islands. Idaho, Pennsylvania and New Mexico formed part of Task Force 52.10 (Rear Admiral Ainsworth), and took part in the pre- and post- invasion bombardment of Saipan (from 14 June). The Idaho then moved on to bombard Guam, before protecting transport ships during the Battle of the Philippine Sea (19-21 June 1944). She returned to Guam for a pre invasion bombardment on 12 July, which continued until the invasion on 20 July. She then remained off Guam to help the troops until the end of July.

After brief repairs in a floating dry dock the Idaho took part in the invasion of Peleliu, bombarding the island from 12-24 September. She then returned to Bremerton, Washington State, where she underwent a refit.

In January 1945 the Idaho joined Task Force 54 (Admiral Rodgers) with Tennessee, Nevada, New York and Arkansas. This task force helped support the invasion of Iwo Jima, bombarding enemy positions from 16 February to 7 March.

The ten active 'old' battleships were formed together in Task Force 54 (Rear Admiral Deyo). The Idaho was part of the Gunfire and Covering Group, and flagship of Group 4 (Idaho and West Virginia). The ten battleships were split into five groups: Group 1: Texas, Maryland; Group 2 Arkansas, Colorado; Group 3 Tennessee and Nevada; Group 4 Idaho, West Virginia; Group 5 New Mexico and New York.

Physical Training, USS Idaho (BB-42) , 1920
Physical Training, USS Idaho (BB-42) , 1920

The Idaho began bombardment Japanese positions on Okinawa on 25 March. The island was invaded on 1 April, and the Japanese threw massed waves of kamikaze aircraft against the American fleet. The Idaho was damaged by a near miss on 12 April, and needed repairs at Guam. These were quickly completed and she was back and firing again on 22 May. The Idaho remained off Okinawa until 20 June, when she sailed for Leyte Gulf and practise exercises for the planned invasion of Japan.

After the Japanese surrender the Idaho formed part of the fleet that entered Tokyo Bay to witness the Japanese surrender. After the war she was quickly decommissions, and was sold for scrap in November 1947.

Displacement (standard)


Displacement (loaded)


Top Speed



8,000nm at 10kts

Armour – belt


 - deck


 - turret faces

18in or 16in

 - turret sides


 - turret top


 - turret rear


 - barbettes


 - coning tower


 - coning tower top





97ft 5in


Twelve 14in guns in four triple turrets
Fourteen 4in guns
Four 3in guns
Two 21in submerged beam torpedo tubes

Crew complement


Laid down

20 January 1915


30 June 1917


24 March 1919


Stricken 1947

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How to cite this article: Rickard, J (26 September 2011), USS Idaho (BB 42) ,

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