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The ''Iowa''-class battleships were a class of fast battleships ordered by the United States Navy in 1939 and 1940 to escort the Fast Carrier Task Forces that would operate in the Pacific Theater of World War II. Four were completed; two more were laid down but canceled at war's end and scrapped. Like other third-generation American battleships, the ''Iowa'' class followed the design pattern set forth in the preceding and battleships, which emphasized speed and the secondary and anti-aircraft batteries.〔Hough, pp. 214–216.〕 Between the mid-1940s and the early 1990s, the ''Iowa''-class battleships fought in four major U.S. wars. In World War II, they defended aircraft carriers and shelled Japanese positions. During the Korean War, the battleships provided seaborne artillery support for United Nations forces fighting North Korea, and in 1968, ' shelled Viet Cong and Vietnam People's Army forces in the Vietnam War. All four were reactivated and armed with missiles during the 1980s as part of the 600-ship Navy initiative; during Operation Desert Storm in 1991, ''Missouri'' and ''Wisconsin'' fired missiles and guns at Iraqi targets. Costly to maintain, the battleships were decommissioned during the post-Cold War draw down in the early 1990s. All four were initially removed from the Naval Vessel Register; however, the United States Congress compelled the Navy to reinstate two of them on the grounds that existing naval gunfire support would be inadequate for amphibious operations. This resulted in a lengthy debate over whether battleships should have a role in the modern navy. Ultimately, all four ships were stricken from the Naval Vessel Register and released for donation to non-profit organizations. With the transfer of in 2012, all four are part of various non-profit maritime museums across the U.S. == Background == Work on what would eventually become the ''Iowa''-class battleships began on the first study in early 1938 at the direction of Admiral Thomas C. Hart, head of the General Board. It was an expanded ''South Dakota'', carrying either twelve 16-inch/45 caliber Mark 6 guns or nine 18-inch (460 mm) guns—the latter armament being dropped after the 31 March agreement—with more armor and a power plant large enough to drive the larger ship through the water at the same speed as the ''South Dakota''s, .〔Garzke and Dulin, p. 107.〕 These studies had no further impact on the design of the ''Iowa'' class, but development of this design continued and eventually evolved into the design for the .〔Friedman, pp. 309, 311.〕 Another design, pursued by the Design Division section of the Bureau of Construction and Repair, was a "cruiser-killer." Beginning on 17 January 1938 under Captain A. J. Chantry, the group drew up plans for ships with twelve 16-inch and twenty 5-inch guns, Panamax capability but otherwise unlimited displacement, a top speed of and a range of when traveling at the more economical speed of . Their plan fulfilled these requirements with a ship of , but Chantry believed that more could be done if the ship were to be this large; with a displacement greater than that of most battleships, its armor would only have protected it against the 8-inch (203 mm) weapons carried by heavy cruisers.〔Friedman, p. 309.〕 Three improved plans—"A", "B", and "C"—were designed at the end of January. An increase in draft, vast additions to the armor, and the substitution of twelve guns in the secondary battery was common between the three designs. "A" was the largest, at , and was the only one to still carry the twelve 16-inch guns in four triple turrets. It required 277,000 shaft horsepower (shp) to make . "B" was the smallest at ; like "A" it had a top speed of 32.5 knots, but "B" only required 225,000 shp to make this speed. It also carried only nine 16-inch guns, in three triple turrets. "C" was similar but it added 75,000 shp (for a total of 300,000 shp), to make the original requirement of 35 knots. The weight required for this and a longer belt—, compared with for "B"—meant that the ship was .〔Friedman, p. 310.〕 In March 1938, the General Board followed the recommendations of the Battleship Design Advisory Board, which was composed of the naval architect William Francis Gibbs, William Hovgaard (then president of New York Shipbuilding), John Metten, Joseph W. Powell, and the long-retired Admiral and former Chief of the Bureau of Ordnance Joseph Strauss. The board requested an entirely new design study, focusing on increasing the size of the 35,000 ton ''South Dakota'' class. The first plans made for this indicated that was possible on a displacement of about . could be bought with 220,000 shaft horsepower and a displacement of around , which was well below the Second London Naval Treaty's maximum limit of .〔Friedman, pp. 271, 309.〕 These designs were able to convince the General Board that a reasonably well-designed and balanced battleship was possible within the terms of the "escalator clause". However, further studies revealed major problems with the estimates. The speed of the ships meant that more freeboard would be needed both fore and amidships, the latter requiring an additional foot of ''armored'' freeboard. Along with this came the associated weight in supporting these new strains: the structure of the ship had to be reinforced and the power plant enlarged to avoid a drop in speed. In all, about had to be added, and the large margin the navy designers had previously thought they had—roughly —was suddenly vanishing.〔Friedman, pp. 309–310.〕 With the additional displacement, the General Board was incredulous that a tonnage increase of would only allow the addition of s over the ''South Dakota''s. Rather than retaining the 16"/45 caliber Mark 6 gun used in the ''South Dakota''s, they ordered that future studies would have to include the more powerful (but heavier) 16"/50 caliber Mark 2 guns left over from the canceled s and battleships of the early 1920s. It also allowed the draft of the ships to be increased, meaning that the ships could be shortened (lowering weight) and the power reduced (since a narrower beam reduces drag).〔Friedman, pp. 310–311.〕 The 50-caliber gun weighed some more than the 45 caliber did; the barbette size also had to be increased so the total weight gain was about , putting the ship at a total of —well over the 45,000 long ton limit. An apparent savior appeared in a Bureau of Ordnance preliminary design for a turret that could carry the 50 caliber guns in a smaller barbette. This breakthrough was shown to the General Board as part of a series of designs on 2 June 1938.〔Friedman, p. 311.〕 However, the Bureau of Ordnance continued working on a larger barbette design, while the Bureau of Construction and Repair utilized the smaller barbettes in the final planning of the new battleships. As the bureaus were independent of one another, they did not realize that the two plans could not go together until November 1938, when the design was in the final stages of refinement. By this time, the ships could not use the larger barbette, as it would require massive alterations to the design and would result in substantial weight penalties. The General Board was astounded; one member asked the head of the Bureau of Ordnance if it had occurred to him that Construction and Repair would have wanted to know what turret his subordinates were working on "as a matter of common sense". A complete scrapping of plans was only avoided when designers within the Bureau of Ordnance were able to design a new 50-caliber gun, the Mark 7, that was both lighter and smaller in outside diameter; this allowed it to be placed in a turret that would fit in the smaller barbette.〔Friedman, pp. 311–312.〕 The redesigned 3-gun turret, equipped as it was with the Mark 7 naval gun, provided an overall weight saving of nearly to the overall design of the ''Iowa'' class.〔Lyon, p. 240.〕 In May 1938 the United States Congress passed the Second Vinson Act which "mandated a 20% increase in strength of the United States Navy".〔Rogers: Fastest Battleships〕 The act was sponsored by Carl Vinson, a Democratic Congressman from Georgia who was Chairman of the House Naval Affairs and Armed Services Committee.〔Vinson: Congressional biography〕 The Second Vinson Act updated the provisions of the Vinson-Trammell Act of 1934 and the Naval Act (1936), which had "authorized the construction of the first American battleships in 17 years", based on the provisions of the London Naval Treaty of 1930;〔 this act provided the funding to build the ''Iowa'' class. Each ship cost approximately US$100 million.〔Newhart, p. 92.〕 As 1938 drew to a close the design of the ''Iowa''s was nearly complete, but it would continuously evolve as the battleships were under construction. These revisions included changing the design of the foremast, replacing the original 1.1"/75-caliber guns that were to be used for anti-aircraft work with 20 mm and 40 mm guns, and moving the combat information center into the armored hull.〔Stillwell, p. 16.〕 Additionally, in November 1939 the New York Navy Yard greatly modified the internal subdivision of the machinery rooms, as tests had shown the underwater protection in these rooms to be inadequate. The result of this was clearly beneficial: "The prospective effect of flooding was roughly halved and the number of uptakes and hence of openings in the third deck greatly reduced."〔Friedman, p. 313.〕 Although the changes meant extra weight and added to the beam, this was no longer a major issue; the United Kingdom and France had renounced the Second London Naval Treaty soon after the beginning of the Second World War.〔Friedman, pp. 313–314.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Iowa-class battleship」の詳細全文を読む スポンサード リンク
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