The Pacific War Online Encyclopedia

New Mexico Class, U.S. Battleships

Schematic of New Mexico class battleship

ONI 222

Tonnage	33,420 tons standard displacement
Dimensions	624' by 106'3" by 34' 190.20m by 32.39m by 10.36
Maximum speed	21.5 knots
Complement	1443
Aircraft	2 catapult 3 seaplanes
Armament	4x3 14"/50 guns 12x1 5"/51 guns 6x1 5"/25 AA guns 4x4 1.1"/75 AA guns 8x1 20mm Oerlikon AA guns 8 0.50 machine guns
Protection	About 11,000 tons or 32.9% of displacement: 13.5" (343mm) belt tapering to 8" (203mm) below the waterline 2" STS + 1.75" STS + 1.75" NS = 4.2" (51mm STS + 44mm STS + 44mm NS = 107mm) armor deck 4.5" STS + 1.75" MS = 5.5" (114mm STS + 44mm MS = 158mm) over steering spaces 2" STS + 1" STS + 0.5"/1.5" STS + 0.5" MS = 3.1"/3.9" (51mm STS + 25mm STS + 13mm/38mm STS + 13mm MS = 79mm/99mm) splinter deck 13" (330mm) bulkheads tapering to 8" (203mm) below waterline 18"/5"STS/10"/9" (457mm/127mm STS/254mm/229mm) turret 13" (330mm) barbettes Splinter protection for 5"/25 guns 16" (406mm) conning tower 9" (229mm) uptakes 19' (5.8m) underwater protection consisting of a 0.25" (6mm) retaining bulkhead, an inner 1.5"+1.5" (38mm+38mm) STS torpedo bulkhead, an outer 0.75" (19mm) STS torpedo bulkhead, and blisters. The system was designed to withstand a 300 lb (136 kg) explosive charge.
Machinery	4-shaft Westinghouse geared turbine (40,000 shp) 4 White-Foster (New Mexico) or 6 Bureau Express (other units) boilers
Bunkerage	3795 tons fuel oil
Range	12,500 nautical miles (23,000 km) at 18 knots
Modifications	New Mexico and Mississippi: 1942-11: 4 5" guns replaced with 2x4 20mm guns, 6x1 20mm guns. 1943: One catapult landed. 1943-10: Light antiaircraft upgraded to 6x4, 2x2 40mm Bofors AA guns and 24 to 29 20mm guns. 1944: 20mm battery increased to 50 guns. Late 1944: Antiaircraft battery upgraded to 6 5"/51 guns, 10x4 40mm guns, and 40 to 46 20mm guns. 1945: Mississippi upgraded to 16 5"/25 guns, 12x4 40mm guns, and 40 20mm guns with conning tower removed to compensate. Idaho: 1942: Antiaircraft upgraded to 8 5"/25 guns, 10x4 40mm guns, and 16 20mm guns. 1943-2: 20mm battery increased to 43 guns. 1945-1: All 5"25 guns removed and replaced with 10x1 5"38 dual-purpose guns.

The New Mexicos were completed in 1918. The third of the "standard battleship" classes, they were quite similar to the Pennsylvanias, a proposal to build 16" (406mm) gun battleships with heavier armor having been rejected by the Secretary of the Navy as too costly. The newer ships were better sea boats, with clipper bows and a secondary battery located higher in the superstructure, and had improved subdivision. Their triple turrets were built up entirely of flat plates and incorporated independent sliders so that a hit on a single gun would not knock out all three. The guns were a more powerful 14"/50 model than the 14"/45 guns on the earlier ships.

In 1930, the ships were modernized, receiving an antiaircraft battery, a massive bridge structure, better endurance, and a modest amount of additional deck armor. The deck armor was believed capable of resisting a 1600 lb (726 kg) bomb dropped from up to 6000' (1830m). The casemate guns were removed and the casemates plated over.

Stationed in the Atlantic at the time of Pearl Harbor, the New Mexicos were hastily refitted with additional antiaircraft guns and rushed to the Pacific to form the backbone of a new battle line. This precluded any further modernization other than the installation of numerous additional antiaircraft weapons. Only the Idaho ever received the excellent 5"/38 gun.