Belt armor

Belt armor is a layer of heavy metal armor plated onto or within the outer hulls of warships, typically on battleships, battlecruisers and cruisers, and aircraft carriers.

The belt armor is designed to prevent projectiles from penetrating to the heart of a warship. When struck by an artillery shell or underwater torpedo, the belt armor either absorbs the impact and explosion with its sheer thickness and strength, or else uses sloping to redirect the projectile and its blast downwards.

Typically, the main armor belt covers the warship from its main deck down to some distance below the waterline. If, instead of forming the outer hull, the armor belt is built inside the hull, it is installed at a sloped angle for improved protection, as described above.

WWI style ship armor
Diagram of common elements of warship armor. The belt armor (A) is on the exterior, at the waterline. Also indicated is the main deck (B), the sloping deck armor (C), and the torpedo bulkhead (D).

The torpedo bulkhead

KGV Tirpitz armour and underwater protection
Armor and underwater protection of King George V and Tirpitz.
USS Oklahoma (BB37)- Salvage, 12-31-43, 7126-43, Port side at about fr 60 after removal of main patch in drydock - NARA - 296956
Belt armor on damaged USS Oklahoma (BB-37).

Frequently, the main belt's armor plates were supplemented with a torpedo bulkhead spaced several meters behind the main belt, designed to maintain the ship's watertight integrity even if the main belt was penetrated. Furthermore, the outer spaces around the main belt in some designs were filled with storage tanks that could contain fuel oil, seawater, or fresh water. The liquids in these tanks absorb or scatter much of the explosive force of warheads and shells. In other designs, the outer spaces were left empty, allowing some of the initial blast wave to dissipate, while the inner liquid layers then absorbed shrapnel and spread the shock wave out over a larger area. To deal with the leakage from the tanks and incoming seawater, an armored holding bulkhead prevented liquid from entering other parts of the ship. This multilayer design is featured in the cross-sectional drawings of Tirpitz and King George V.[1]

A warship can be seriously damaged underwater not only by torpedoes, but also by heavy naval artillery shells that plunge into the ocean very close to the targeted ship. Such shells which are usually armor-piercing shells (AP shells) can pass through a short stretch of water and strike the warship some distance below the waterline. In 1914 typical AP shells were expected to punch a hole in the exterior plate and detonate there with a destructive effect similar to a torpedo. However by the 1940s, advances in AP shell technology incorporated delayed fuses which give AP shells deep penetration capability before exploding; such AP shells will typically make a smaller hole than a torpedo in breaching a ship's hull, but detonating beyond the belt in the hull can cause splinter damage to machinery spaces and secondary magazines, which in turn compromises watertight integrity and encourages progressive flooding.[2] To improve protection against both shells and torpedoes, an air space can be added between the torpedo belt and the hull to increase the buoyancy of the warship.

Thinning the belt armor

Some kinds of naval warships have belt armor thinner than actually necessary for protection against projectiles. This is common especially with battlecruisers and aircraft carriers to reduce their weight, thus increasing their acceleration and speed. Another possible reason is to meet treaty restrictions on ship displacement. One such method is all-or-nothing armoring, where belt armor is stripped from areas deemed non-vital to the functioning of the ship in battle. Agility gained from such processes is a great asset to offensive warships, which seek to quickly bring their heavy striking power to the enemy. In carriers, the maneuverability is exploited when deploying and recovering aircraft. Since planes take off and land most easily when flying into the wind, the aircraft carrier steams rapidly into the wind in both maneuvers, making take-off and landing safer and easier. To this end, nearly all large aircraft carriers have had speeds of 30 knots or more: for example, the sister ships USS Lexington and USS Saratoga, the second and third aircraft carriers to enter the U.S. Navy, in 1927.

Aircraft carriers typically had even thinner belt armor, despite being expected to face the threat of dive bombers and torpedo bombers more so than other warships. Unlike battleships and battlecruisers, aircraft carriers were not expected to face torpedoes and naval artillery from other surface ships, instead being deployed at a stand-off distance while being escorted by destroyers and cruisers. The British designed and constructed their carriers with Armoured flight decks, which did reduce their aircraft complement and its associated striking and combat air patrol capabilities, but the deck armor was a successful passive defense prior to the establishment of a successful fighter defenses (which required effective radar, high-speed monoplanes, and coordination).

Footnotes

  1. ^ "History and Technology - Torpedo Defense Systems of World War II - NavWeaps". www.navweaps.com.
  2. ^ http://www.navweaps.com/index_lundgren/Kirishima_Damage_Analysis.pdf

External links

See also

Armored cruiser

The armored cruiser was a type of warship of the late 19th and early 20th centuries. It was designed like other types of cruisers to operate as a long-range, independent warship, capable of defeating any ship apart from a battleship and fast enough to outrun any battleship it encountered. Varying in size, it was distinguished from other types of cruiser by its belt armor—thick iron (or later steel) plating on much of the hull to protect the ship from shellfire much like that on battleships. The first armored cruiser, the Imperial Russian Navy's General-Admiral, was launched in 1873 and combined sail and steam propulsion. By the 1890s cruisers had abandoned sail and took on a modern appearance.

For many decades naval technology had not advanced far enough for designers to produce a cruiser which combined an armored belt with the long range and high speed required to fulfill its mission; for this reason, many navies preferred to build protected cruisers in the 1880s and early 1890s. It was often possible to build cruisers which were faster and better all-round using this type of ship, which relied on a lighter armored deck to protect the vital parts of the ship; however, by the late 1880s the development of rapid-fire cannon and high-explosive shells made the reintroduction of side armor a necessity. The invention of face-hardened armor in the mid-1890s offered effective protection with less weight than previously.

In 1908 the armored cruiser was supplanted by the battlecruiser which, with armament equivalent to that of a dreadnought battleship and steam turbine engines, was faster and more powerful than armored cruisers. At around the same time, the term "light cruiser" came into use for small cruisers with armored belts. Despite the fact they were now considered second-rate ships, armored cruisers were widely used in World War I. Most surviving armored cruisers from this conflict were scrapped under the terms of the Washington Naval Treaty of 1922, which imposed limits on warships and defined a cruiser as a ship of 10,000 tons or less carrying guns of 8-inch caliber or less—rather smaller than many of the large armored cruisers. A handful survived in one form or another until World War II.

Caio Duilio-class ironclad

The Caio Duilio class was a pair of ironclad turret ships built for the Royal Italian Navy (Regia Marina) in the 1870s and 1880s. The two ships, Caio Duilio and Enrico Dandolo, were fitted with the largest guns available, 17.72 in (450 mm) rifled muzzle-loading guns, and were the largest, fastest and most powerful ships of their day. To save weight on such large vessels, the ship's designer, Benedetto Brin adopted a radical solution for the time: he reserved armor only for the central portion of the ship where it protected the ships' engines and ammunition magazines, while the rest of the hull were extensively sub-divided with watertight compartments.

Both ships had uneventful careers. They spent the majority of their time in service with the Active and Reserve Squadrons of the main Italian fleet. There, they were primarily occupied with conducting training exercises. In 1895–1898, Enrico Dandolo was heavily reconstructed, but the excessive cost of the modernization prevented Caio Duilio from being similarly rebuilt. Both ships were reassigned as training ships in the early to mid-1900s. Caio Duilio was stricken from the naval register in 1909 and converted into a floating oil tank, while Enrico Dandolo remained in service as a guard ship during World War I. She was sent to the breaker's yard in 1920. Caio Duilio's ultimate fate is unknown.

Indiana-class battleship

The Indiana-class was a class of three coastal defense battleships launched in 1893. They were the first battleships built by the United States Navy comparable to contemporary European ships, such as the British HMS Hood. Authorized in 1890 and commissioned between November 1895 and April 1896, they were relatively small battleships with heavy armor and ordnance that pioneered the use of an intermediate battery. Specifically intended for coastal defense, their freeboard was insufficient to deal well with the waves of the open ocean. Their turrets lacked counterweights, and the main belt armor was placed too low to be effective under most conditions.

The ships were named Indiana, Massachusetts, and Oregon and were designated Battleship Number 1 through 3. All three served in the Spanish–American War, although Oregon—which was stationed on the West Coast—had to cruise 14,000 nautical miles (26,000 km; 16,000 mi) around South America to the East Coast first. After the war, Oregon returned to the Pacific and participated in the Philippine–American War and Boxer Rebellion, while her sister ships were restricted to training missions in the Atlantic Ocean. After 1903, the obsolete battleships were de- and recommissioned several times, the last time during World War I when Indiana and Massachusetts served as training ships, while Oregon was a transport escort for the Siberian Intervention.

In 1919, all three ships were decommissioned for the final time. Indiana was sunk in shallow water as an explosives test target a year later and sold for scrap in 1924. Massachusetts was scuttled off the coast of Pensacola in 1920 and used as an artillery target. The wreck was never scrapped and is now a Florida Underwater Archaeological Preserve. Oregon was initially preserved as a museum, but was sold for scrap during World War II. The scrapping was later halted and the stripped hulk was used as an ammunition barge during the battle of Guam. The hulk was finally sold for scrap in 1956.

Italia-class ironclad

The Italia class was a class of two ironclad battleships built for the Italian Regia Marina (Royal Navy) in the 1870s and 1880s. The two ships—Italia and Lepanto—were designed by Benedetto Brin, who chose to discard traditional belt armor entirely, relying on a combination of very high speed and extensive internal subdivision to protect the ships. This, along with their armament of very large 17-inch (430 mm) guns, has led some naval historians to refer to the Italia class as prototypical battlecruisers.

Despite serving for over thirty years, the ships had uneventful careers. They spent their first two decades in service with the Active and Reserve Squadrons, where they were primarily occupied with training maneuvers. Lepanto was converted into a training ship in 1902 and Italia was significantly modernized in 1905–08 before also becoming a training ship. They briefly saw action during the Italo-Turkish War, where they provided gunfire support to Italian troops defending Tripoli. Lepanto was discarded in early 1915, though Italia continued on as a guard ship during World War I, eventually being converted into a grain transport. She was ultimately broken up for scrap in 1921.

Italian ironclad Andrea Doria

Andrea Doria was an ironclad battleship built for the Italian Regia Marina (Royal Navy) in the 1880s and 1890s. Named for the 16th-century Genoese admiral Andrea Doria, she was the third and final ship of the Ruggiero di Lauria class. The ship was armed with a main battery of four 17-inch (432 mm) guns, was protected with 17.75-inch (451 mm) thick belt armor, and was capable of a top speed of 17 knots (31 km/h; 20 mph).

The ship's construction period was very lengthy, beginning in August 1881 and completing in February 1888. She was quickly rendered obsolescent by the new pre-dreadnought battleships being laid down, and as a result, her career was limited. She spent her career alternating between the Active and Reserve Squadrons, where she took part in training exercises each year with the rest of the fleet. Andrea Doria was stricken from the naval register in 1911 and used as a depot ship until Italy entered World War I in 1915. The ship was renamed GR 104 and employed as a guard ship in Brindisi. She was converted into a floating oil tank after the war and was eventually broken up for scrap in 1929.

Italian ironclad Francesco Morosini

Francesco Morosini was an ironclad battleship built in the 1880s and 1890s for the Italian Regia Marina (Royal Navy). The ship, named for Francesco Morosini, the 17th-century Doge of Venice, was the second of three ships in the Ruggiero di Lauria class, along with Ruggiero di Lauria and Andrea Doria. She was armed with a main battery of four 17-inch (432 mm) guns, was protected with 17.75-inch (451 mm) thick belt armor, and was capable of a top speed of 17 knots (31 km/h; 20 mph).

The ship's construction period was very lengthy, beginning in August 1881 and completing in February 1888. She was quickly rendered obsolescent by the new pre-dreadnought battleships being laid down, and as a result, her career was limited. She spent her career alternating between the Active and Reserve Squadrons, where she took part in training exercises each year with the rest of the fleet. The ship was stricken from the naval register in August 1909; the following month, she was expended as a target ship for experiments with torpedoes.

Italian ironclad Italia

Italia was an Italian ironclad battleship build for the Italian Regia Marina (Royal Navy), the lead ship of the Italia class. She and her single sister ship, Lepanto, had lengthy construction times. Italia was laid down in January 1876, launched in September 1880, and completed in October 1885. She was armed with a main battery of four 17 in (432 mm) guns mounted in a central barbette and was capable of a top speed of 17.8 knots (33.0 km/h; 20.5 mph). Unusually, for ships of that era, Italia had an armored deck rather than the typical belt armor.

Italia spent the first two decades of her career in the Active and Reserve Squadrons, where she took part in annual training maneuvers with the rest of the fleet. She was withdrawn from service in 1905 for a significant modernization. Upon returning to service in 1909, Italia was employed as a training ship. During the Italo-Turkish War of 1911–1912, the ship provided fire support to Italian troops defending Tripoli in Libya. She was used as a floating battery at Brindisi after Italy entered World War I in 1915. The ship was rebuilt as a grain carrier in December 1917 – June 1918. Italia served in this capacity for only a short time, being stricken in November 1921 and then scrapped.

Italian ironclad Lepanto

Lepanto was an Italian ironclad battleship built for the Italian Regia Marina (Royal Navy), the second and last ship of the Italia class. Lepanto was laid down in November 1876, launched in March 1883, and completed in August 1887. She was armed with a main battery of four 17 in (432 mm) guns mounted in a central barbette and was capable of a top speed of 17.8 knots (33.0 km/h; 20.5 mph). Unlike other capital ships of the era, Lepanto had an armored deck rather than the more typical belt armor.

Lepanto spent the first two decades of her career in the Active and Reserve Squadrons, where she took part in annual training maneuvers with the rest of the fleet. In 1902, she was withdrawn from service for use as a training ship. During the Italo-Turkish War of 1911–1912, the ship provided fire support to Italian troops defending Tripoli in Libya. Lepanto was ultimately stricken from the naval register in January 1914 and sold for scrapping in March 1915.

Italian ironclad Ruggiero di Lauria

Ruggiero di Lauria was an ironclad battleship built in the 1880s for the Italian Regia Marina (Royal Navy). She was the lead ship of the Ruggiero di Lauria class, which included two other ships, Francesco Morosini and Andrea Doria. Ruggiero di Lauria, named for the medieval Sicilian admiral Ruggiero di Lauria, was armed with a main battery of four 17-inch (432 mm) guns, was protected with 17.75-inch (451 mm) thick belt armor, and was capable of a top speed of 17 knots (31 km/h; 20 mph).

The ship's construction period was very lengthy, beginning in August 1881 and completing in February 1888. She was quickly rendered obsolescent by the new pre-dreadnought battleships being laid down and, as a result, her career was limited. She spent her career alternating between the Active and Reserve Squadrons, where she took part in training exercises each year with the rest of the fleet. The ship was stricken from the naval register in 1909 and converted into a floating oil tank. She was used in this capacity until 1943, when she was sunk by bombs during World War II. The wreck was eventually raised and scrapped in 1945.

Italian ironclad Venezia

Venezia was the second of two Roma-class ironclad warships built for the Italian Regia Marina in the 1860s. She was armed with a main battery of eighteen 10-inch (250 mm) guns in a central armored casemate. Her lengthy construction time, a result of her re-design from a broadside ironclad, quickly rendered her obsolescent compared to the new turret ships that began to enter service in the 1880s. As a result, her career was limited. She became a training ship in 1881 and served until 1895. Venezia was broken up for scrap the next year.

Japanese aircraft carrier Taihō

Taihō (大鳳) (meaning Great Phoenix), was an aircraft carrier of the Imperial Japanese Navy during World War II. Possessing heavy belt armor and featuring an armored flight deck (a first for any Japanese aircraft carrier), she represented a major departure in Japanese aircraft carrier design and was expected to not only survive multiple bomb, torpedo, or shell hits, but also continue fighting effectively afterwards.

Built by Kawasaki at Kobe, she was laid down on 10 July 1941, launched almost two years later on 7 April 1943 and finally commissioned on 7 March 1944. She sank on 19 June 1944 during the Battle of the Philippine Sea after suffering a single torpedo hit from an American submarine, due to explosions resulting from design flaws and poor damage control.

L 20e α-class battleship

L 20e α was a design for a class of battleships to be built in 1918 for the German Kaiserliche Marine (Imperial Navy) during World War I. Design work on the class of battleship to succeed the Bayern-class battleships began in 1914, but the outbreak of World War I in July 1914 led to these plans being shelved. Work resumed in early 1916 and lessons from the Battle of Jutland, fought later that year, were incorporated into the design. Reinhard Scheer, the commander of the fleet, wanted larger main guns and a higher top speed than earlier vessels, to combat the latest ships in the British Royal Navy. A variety of proposals were submitted, with armament ranging from the same eight 38 cm (15 in) guns of the Bayern class to eight 42 cm (16.5 in) guns.

Work on the design was completed by September 1918, but by then there was no chance for them to be built. Germany's declining war situation and the reallocation of resources to support the U-boat campaign meant that the ships would never be built. The ships would have been significantly larger than the preceding Bayern-class battleships, at 238 m (780 ft 10 in) long, compared to 180 m (590 ft 7 in) for the preceding ships. The L 20e α class would have been significantly faster, with a top speed of 26 knots (48 km/h; 30 mph), compared to the 21-knot (39 km/h; 24 mph) maximum of the Bayerns and would have been the first German warships to have mounted guns larger than 38 cm.

Richelieu-class battleship

The Richelieu class were fast battleships built for the French Navy between the 1930s and 1950s. Initially two ships were ordered in 1935 in response to Italian orders for the Littorio-class battleships the previous year. The Richelieus were based on the preceding Dunkerque class, but scaled up to accommodate more powerful 380 mm (15 in) guns and armor to protect them from guns of the same caliber. To keep the ships within the displacement limits imposed by the Washington Naval Treaty, they featured the same concentrated arrangement as the Dunkerques for the main battery: two quadruple gun turrets placed forward. They also incorporated new, more compact boilers that allowed for a shorter hull (which required less heavy armor) for the desired top speed. After Germany ordered two Bismarck-class battleships, France responded with another pair of Richelieus, but built to modified designs. The first, Clemenceau, received modified secondary and anti-aircraft batteries, while Gascogne had her superfiring main battery turret shifted aft, along with other changes.

None of the members of the class had been completed by the outbreak of World War II. Richelieu was finished shortly before the French defeat in the Battle of France, while Jean Bart was hurriedly prepared to be ready to go to sea during the campaign. Both vessels fled to French colonies in Africa: Richelieu steamed to Dakar and Jean Bart went to Casablanca. Work on Clemenceau and Gascogne stopped after the Germans occupied France. In mid-1940, Richelieu was attacked twice and damaged by British forces attempting to coerce the crew to defect to Free France, while Jean Bart was badly damaged by American forces during Operation Torch in November 1942. After the French African colonies shifted to Free French control, Richelieu was taken to the United States to be repaired and modernized, while Jean Bart was not completed. Richelieu saw active service with the British Home Fleet in early 1944 before being transferred to the Eastern Fleet later that year. There, she took part in numerous operations against Japanese forces in the Indian Ocean. She was present for the Japanese surrender of Singapore at the end of the war.

After the war, Richelieu took part in the initial campaign to restore control of French Indochina before returning to France, where she saw limited activity into the early 1950s. During this period, the French Navy discussed proposals to complete Jean Bart or convert her into an aircraft carrier, ultimately settling on the former. She was finally commissioned in 1955, thereafter taking part in the French intervention in the Suez Crisis in November 1956. Her career proved to be a short one, and she was placed in reserve in 1957. Both vessels were used as training and barracks ships into the 1960s; Richelieu was sold to ship breakers in 1968 and Jean Bart followed her in 1970.

South Dakota-class battleship (1939)

The South Dakota class was a group of four fast battleships built by the United States Navy. They were the second class of battleships to be named after the 40th state; the first were designed in the 1920s and canceled under the terms of the Washington Naval Treaty.

Four ships comprised the class: South Dakota, Indiana, Massachusetts, and Alabama. They were designed to the same treaty standard displacement limit of 35,000 long tons (35,600 t) as the preceding North Carolina class and had the same main battery of nine 16"/45 caliber Mark 6 guns in three-gun turrets, but were more compact and better protected. The ships can be visually distinguished from the earlier vessels by their single funnel, compared to twin funnels in the North Carolinas. According to naval historians William Garzke and Robert Dulin, the South Dakota design was the best "treaty battleship" ever built.Construction began shortly before World War II, with Fiscal Year (FY) 1939 appropriations. Commissioning through the summer of 1942, the four ships served in both the Atlantic, ready to intercept possible German capital ship sorties, and the Pacific, in carrier groups and shore bombardments. All four ships were retired shortly after World War II; South Dakota and Indiana were scrapped in the 1960's, Massachusetts and Alabama were retained as museum ships.

Torpedo bulkhead

A torpedo bulkhead is a type of armor common on the more heavily armored warships, especially battleships and battlecruisers of the early 20th century. It is designed to keep the ship afloat even if the hull was struck underneath the belt armor by a shell or by a torpedo.

USS Idaho (BB-42)

USS Idaho (BB-42), a New Mexico-class battleship, was the fourth ship of the United States Navy to be named for the 43rd state. She was the third of three ships of her class. Built by the New York Shipbuilding Corporation of Camden, New Jersey, she was launched in June 1917 and commissioned in March 1919. She was armed with a battery of twelve 14-inch (356 mm) guns in four three-gun turrets, and was protected by heavy armor plate, with her main belt armor being 13.5 inches (343 mm) thick.

Idaho spent most of the 1920s and 1930s in the Pacific Fleet, where she conducted routine training exercises. Like her sister ships, she was modernized in the early 1930s. In mid-1941, before the United States entered World War II, Idaho and her sisters were sent to join the Neutrality Patrols that protected American shipping during the Battle of the Atlantic. After Japan attacked Pearl Harbor on 7 December 1941, Idaho and her sisters were sent to the Pacific, where she supported amphibious operations in the Pacific. She shelled Japanese forces during the Gilbert and Marshall Islands and the Philippines campaigns and the invasions of Peleliu, Iwo Jima, and Okinawa.

Idaho was among the ships present in Tokyo Bay when Japan formally surrendered on 2 September 1945. With the war over, the ship was decommissioned in July 1946. She was sold to ship breakers in November 1947 and subsequently dismantled.

USS Mississippi (BB-41)

USS Mississippi (BB-41/AG-128), the second of three members of the New Mexico class, was the third ship of the United States Navy named in honor of the 20th state. The ship was built at the Newport News Shipbuilding Company of Newport News, Virginia, from her keel laying in April 1915, her launching in January 1917, and her commissioning in December that year. She was armed with a battery of twelve 14-inch (356 mm) guns in four three-gun turrets, and was protected by heavy armor plate, with her main belt armor being 13.5 inches (343 mm) thick.

The ship remained in North American waters during World War I, conducting training exercises to work up the crew. Throughout the 1920s and 1930s, the ship served in the Pacific Fleet. In May 1941, with World War II and the Battle of the Atlantic raging, Mississippi and her two sister ships were transferred to the Atlantic Fleet to help protect American shipping through the Neutrality Patrols. Two days after the Japanese attack on Pearl Harbor, Mississippi departed the Atlantic to return to the Pacific Fleet; throughout her participation in World War II, she supported amphibious operations in the Pacific. She shelled Japanese forces during the Gilbert and Marshall Islands and the Philippines campaigns and the invasions of Peleliu and Okinawa. The Japanese fleet attacked American forces during the Philippines campaign, and in the ensuing Battle of Leyte Gulf, Mississippi took part in the Battle of Surigao Strait, the last battleship engagement in history.

After the war, Mississippi was converted into a gunnery training ship, and was also used to test new weapons systems. These included the RIM-2 Terrier missile and the AUM-N-2 Petrel missile. She was eventually decommissioned in 1956 and sold to ship breakers in November that year.

Unit system of machinery

The unit system of machinery was a method of arranging a ship's propulsion machinery into separate units that could each operate autonomously in case of damage to the ship. For a steamship, this would be a boiler room supplying steam to an engine room. There might also be a gearing room that housed the transmission that actually turned the propeller shaft(s). Ideally each "unit" should have an additional compartment between them to further reduce the risk. Many ships were able to provide steam via cross-connections from either boiler room to either engine room.The unit system was developed during World War I to help mitigate damage and flooding from damage inflicted by a weapon and to preserve a ship's mobility by physically separating the engines and boilers into at least two groups so that a single torpedo hit, for example, could not flood all of the boiler or engine rooms, disabling all of the ship's propulsion machinery. A single World War II torpedo hit would typically blow a 35-by-15-foot (10.7 m × 4.6 m) hole in the hull and would compromise the integrity of adjacent watertight bulkheads over twice that length and further if the ship was of riveted construction rather than welded. This would usually flood two compartments and possibly three.The unit system invariably added length to accommodate the additional piping to cross-connect the engines and boilers and the widely separated boilers required two funnels which reduced the fields of fire of the ship's anti-aircraft guns and added topweight. There could be significant knock-on costs as well. For example, the second batch of the British Leander-class light cruisers of the 1930s (which were all eventually sold to Australia) were modified to use the unit system. This increased the length of the machinery spaces by 8 feet (2.4 m) and the waterline belt armor needed to protect the boilers increased by a length of 57 feet (17.4 m). The extra weight of the armor required the beam to be increased by 1 foot 8 inches (0.51 m) to preserve stability. All of these changes made the ships more expensive than their predecessors.

Wyoming-class battleship

The Wyoming class was a pair of dreadnought battleships built for the United States Navy. The Wyoming and Arkansas were authorized in early 1909, and were built between 1910 and 1912. These were the fourth dreadnought design of the US Navy, but only an incremental improvement over the preceding Florida class, and the last US battleships to use 12" guns. The primary changes were the addition of a sixth twin-gun turret, and improved armor protection, including the first use of a torpedo bulkhead on American battleships. The Navy considered using more powerful 14-inch (356 mm) guns, but this would have caused delays and required larger ships.

The two ships frequently served together, first in the Atlantic Fleet in the 1910s. Both vessels were deployed to British waters after the United States entered World War I in April 1917 to reinforce the Royal Navy's Grand Fleet. They served in the Pacific Fleet in 1919–21, before both returned to the Atlantic Fleet. Much of their time in the Atlantic Fleet was spent conducting peacetime training exercises, along with taking midshipmen from the US Naval Academy on training cruises. Wyoming and Arkansas were heavily modernized in the mid-1920s, receiving more efficient oil-fired boilers to replace their old coal-fired models, thicker deck armor to protect against plunging fire, anti-torpedo bulges to increase their resistance to underwater damage, and anti-aircraft guns to defend against aerial attacks.

The London Naval Treaty of 1930 mandated that Wyoming be demilitarized; she accordingly was converted into a training ship, with half of her main battery turrets, belt armor, and anti-torpedo bulges removed. However, Arkansas was permitted to continue in service with the fleet. After the United States entered World War II, Arkansas was used to escort convoys to North Africa. By 1944, she served as a coastal bombardment vessel; in this role, she supported Allied landings at Normandy (Operation Overlord) and southern France (Operation Dragoon) before being transferred to the Pacific, where she provided fire support to Marines fighting on Iwo Jima and at Okinawa in 1945. Wyoming meanwhile continued as a training ship, being modified further in 1944 to include the various types of anti-aircraft guns that trainees would operate in the fleet. Both ships were decommissioned shortly after the war, with Arkansas being expended as a target ship during the 1946 nuclear tests at Operation Crossroads, and Wyoming being sold for scrap in 1947.

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