Tosa class battleship
Encyclopedia
The The ships are sometimes referred to as the Kaga class, after the ship that was planned to have been completed first. battleship
s, known as Design A-127 during early planning, was an Imperial Japanese Navy
dreadnought
class planned as part of the "Eight-Eight
" fleet. The ships were a larger version of the preceding , and mounted an additional dual 16 in (406 mm) gun turret
. The ships were also larger, in both length and beam, and drew
an additional 10 inches (25.4 cm) at full load. The design for the class also served as a basis for the contemporary battlecruisers.
The Tosa class consisted of and . Both were canceled according to the terms of the Washington Naval Treaty
before either could be completed. Tosa was sunk as a gunnery target in the Bungo Channel
, while the incomplete hull of Kaga was converted into an aircraft carrier
.Originally, Kaga was not going to be converted in favor of the two Amagi class. However, was severely damaged in the Great Kantō earthquake
of 1923, so Kaga was converted instead. After having been converted into an aircraft carrier, Kaga took part in the attack on Pearl Harbor
, before eventually being sunk at the Battle of Midway
in 1942.
, who also had taken a lead role in the design of the s.
of 100 feet (30.5 m) and a draft
of 30 in 10 in (9.4 m). Although a turbo-electric
drive was considered for these ships after the United States announced that the plant was a great success in the battleship (the Japanese estimated that a 70000 shp turbo-electric plant could be installed in the Tosa class, which would have given the ships a speed of 25.25 kn (30.7 mph; 49.5 km/h), a 2500 nmi (2,877 mi; 4,630 km) range at full speed, and a 7800 nmi (8,976.1 mi; 14,445.6 km) range at 14 knots, it was rejected, and more conventional Curtis turbines
were chosen. These turbines would have used 4 propeller shafts, and would have been powered by 12 Kampon water-tube boiler
s, 8 of which would have been oil fired, while the other 4 would have mixed oil and coal for fuel. This system would have provided 91000 shp for a top speed of 26.5 knots. The fuel stores would have amounted to 3,600 tons of oil and 1,800 tons of coal; at a speed of 14 knots, this would have enabled a maximum range of 6500 nmi (7,480.1 mi; 12,038 km).
. The guns fired 2205 lbs armor-piercing
projectile
s with a propellant
charge weighing 494 lbs at 2592 feet per second (790 m/s), at a rate of fire between 1.5 to 2.5 rounds per minute. Each gun had 90 rounds, and had an approximate barrel life of 250 to 300 shots. The turrets would have been arranged along the centerline: two superfiring turrets fore, and three in line aft of the superstructure. The gun turrets weighed 1004 long tons (1,020.1 MT), and allowed for depression down to −5° and elevation to 30°.
The secondary battery would have consisted of twenty 5.5 inches (139.7 mm) L/50 guns mounted in casemate
s along the center of the ship. These guns fired 83.8 lbs projectiles and used between 22.8 lbs of propellant at a muzzle velocity
between 2789 and 2805 ft/s (850.1 and 855 m/s). The guns had a maximum elevation of 25°, which enabled a maximum range of 19140 yards. Four—later increased to six—4.7 inches (119.4 mm) L/45 anti-aircraft guns were to have been mounted amidships, along with eight 24 inches (609.6 mm) above-water torpedo tubes.
of armor 11 inches (279.4 mm) thick, sloped at 15°. The belt armor was designed to be able to defeat 16 inches (406.4 mm) shells from a distance of 12000 –. The main battery turrets and barbettes would have had between 9 and 12 in (228.6 and 304.8 mm) of armor plating, and the conning tower
would have had armor 14 inches (355.6 mm) thick. The decks would have been 4 inches (101.6 mm) thick. The Tosa-class battleships would have had a torpedo bulkhead
3 inches (76.2 mm) thick, which connected at the top to a 1.5 inches (38.1 mm) splinter deck beneath the main deck.
convinced naval war planners that more fast capital ships were needed, so on 4 April 1907, the Imperial Defence Council approved an "Eight-Eight
" policy. This plan originally called for a fleet of eight battleship
s and eight armored cruiser
s that would all be under ten years old (later changed to eight battlecruiser
s and reduced to eight years old). However, the advent of the dreadnought
crippled this plan at the beginning; given Japan's economy and the enormous strain that had been put on it during the Russo-Japanese War (Japan emerged from the war victorious, but bankrupt), the launch of HMS Dreadnought
was a "disaster" for Japan.
In 1907, Japan was nominally halfway to the eight-eight with two newly-delivered pre-dreadnought
battleships (the ) in the fleet and two more pre-dreadnoughts (the ) and four armored cruisers authorized or under construction. In addition, three more battleships and four armored cruisers had been authorized, though not funded. However, naval technology was changing; armored cruisers were seemingly obsolete in the face of the new battlecruisers being laid down by Great Britain and Germany. The Imperial Japanese Navy recognized this, and so they proposed in 1909 that two battlecruisers be ordered from British plans, with one to be built in Great Britain and one to be built at home. These two ships became the .
In 1910, there was still authorization for one battleship and four armored cruisers. This battleship, the battleship version of the Kongo-class battlecruisers, became Japan's first super-dreadnought Fuso
. With these ships, Japan appeared to be getting closer to the eight-eight goal; however, these new ships represented a "new level of naval strength" for the IJN, and they made all previous Japanese capital ship obsolete. This meant that any naval planner aiming for an eight-eight fleet would have to call for seven more battleships and four more battlecruisers when Japan was trying to weather a world economic depression.
After proposals from the IJN in 1911 and 1912 for massive shipbuilding programs, the Cabinet compromised down to a "four-four" plan; under this, three new battleships and no new battlecruisers were authorized. However, the Navy did not agree, and instead called for an "eight-four" fleet, while the Imperial Defence Council called for the original eight-eight. The Cabinet relented, and by July 1914, it was decided to go first for an eight-four fleet, followed by the eight-eight fleet. The eight-four plan was presented to the Diet
in 1915; it planned to have the eight battleships and four battlecruisers by 1923 with the building of two and two Tosa-class battleships.
The ships were laid down in 1920, with Tosa being laid down on 16 February 1920 at the Mitsubishi
shipyard in Nagasaki, and Kaga following on 19 July 1920 at the Kawasaki
shipyard in Kobe. Both were launched less than two years after they were laid down; Tosa on 18 December 1921 and Kaga on 17 November 1921. Even though Tosa was laid down first, she was scheduled to be completed in March 1923 while Kagas planned completion date was 25 December 1922. However, the 1922 Washington Naval Treaty
intervened; this mandated the cancellation of all naval ships under construction, including the two Tosa class battleships; construction stopped on both ships on 5 February 1922. After being stricken on 1 April 1924, Tosa was expended as a target
in the Bungo Channel
s on 9 February 1925; she was used as practice for naval gunfire and to test her armor scheme against mines and torpedoes. Accounts of these tests mention that shells struck the ship below the waterline, which could explain later IJN interest in internal armor; the results from all of these tests was used to design the protection of the s.
It was originally planned that Kaga would be scrapped. However, , one of the two battlecruisers which were being converted to aircraft carrier
s, was severely damaged in the Great Kantō earthquake
in 1923 and rendered unusable. This meant that her conversion under the terms of the treatySee: Washington Naval Treaty, Chapter I, Article IX was impossible, so Kaga was reordered as a carrier in her stead; the conversion took 5 years (1923–28).
As originally completed, Kaga seemed to combine the concept of an aircraft carrier with a cruiser; she mounted a cruiser-like ten 8 inches (203.2 mm)/50 caliber guns (two twin turrets mounted on each side of the middle flight deck and six mounted singly in casemates) and had a belt that was 11 in (279.4 mm) thick. The carrier officially displaced about 29,600 t
, although the actual figure was likely closer to 30,000 t; she was capable of steaming for 8000 nautical miles (14,816 km) when going 14 knots, though she was able to go at a maximum of 27.5 knots if needed. Similar to the former Amagi class carrier , Kaga was fitted with two flying-off decks "stepped down" from a flight deck that extended two-thirds of the ship; in theory, this allowed planes to take off directly from the hangars while other planes landed on the top. However, because operations proved dangerous and were impossible to conduct in rough weather, a 1935 reconstruction removed the lower two decks and extended the top flight deck to the bow.
After the reconstruction, Kaga officially displaced 38200 t (37,596.6 LT; 42,108.3 ST) standard; better boilers allowed her to obtain a top speed of around 28 knots, and the aircraft capacity was raised to 90. Interestingly, the ten 8-inch guns, although now all mounted singly in casemates, were retained. After supporting operations in China, Kaga took part in the attack on Pearl Harbor
on 7 December 1941. She covered amphibious assaults for the first three months of 1942, although she hit a reef in February. After receiving repairs for that damage in April, she sailed to support the landings on Midway; however, the IJN was surprised by the appearance of three U.S. carriers, beginning the Battle of Midway
. Due in part to Admiral Isoroku Yamamoto's
plan, in which ships were dispersed and not close enough to mutually support one another, Kaga, along with the other three carriers present, were sunk by U.S. aircraft from , and .
Battleship
A battleship is a large armored warship with a main battery consisting of heavy caliber guns. Battleships were larger, better armed and armored than cruisers and destroyers. As the largest armed ships in a fleet, battleships were used to attain command of the sea and represented the apex of a...
s, known as Design A-127 during early planning, was an Imperial Japanese Navy
Imperial Japanese Navy
The Imperial Japanese Navy was the navy of the Empire of Japan from 1869 until 1947, when it was dissolved following Japan's constitutional renunciation of the use of force as a means of settling international disputes...
dreadnought
Dreadnought
The dreadnought was the predominant type of 20th-century battleship. The first of the kind, the Royal Navy's had such an impact when launched in 1906 that similar battleships built after her were referred to as "dreadnoughts", and earlier battleships became known as pre-dreadnoughts...
class planned as part of the "Eight-Eight
Eight-eight fleet
The was a Japanese naval strategy formulated for the development of the Imperial Japanese Navy in the first quarter of the 20th century, which laid down that the Japanese navy should include eight first-class battleships and eight armoured cruisers or battlecruisers.-History and development:The...
" fleet. The ships were a larger version of the preceding , and mounted an additional dual 16 in (406 mm) gun turret
Gun turret
A gun turret is a weapon mount that protects the crew or mechanism of a projectile-firing weapon and at the same time lets the weapon be aimed and fired in many directions.The turret is also a rotating weapon platform...
. The ships were also larger, in both length and beam, and drew
Draft (hull)
The draft of a ship's hull is the vertical distance between the waterline and the bottom of the hull , with the thickness of the hull included; in the case of not being included the draft outline would be obtained...
an additional 10 inches (25.4 cm) at full load. The design for the class also served as a basis for the contemporary battlecruisers.
The Tosa class consisted of and . Both were canceled according to the terms of the Washington Naval Treaty
Washington Naval Treaty
The Washington Naval Treaty, also known as the Five-Power Treaty, was an attempt to cap and limit, and "prevent 'further' costly escalation" of the naval arms race that had begun after World War I between various International powers, each of which had significant naval fleets. The treaty was...
before either could be completed. Tosa was sunk as a gunnery target in the Bungo Channel
Bungo Channel
The is a strait separating the Japanese islands of Kyūshū and Shikoku. It connects the Pacific Ocean and Seto Inland Sea. The narrowest part of this channel is the Hōyo Strait....
, while the incomplete hull of Kaga was converted into an aircraft carrier
Aircraft carrier
An aircraft carrier is a warship designed with a primary mission of deploying and recovering aircraft, acting as a seagoing airbase. Aircraft carriers thus allow a naval force to project air power worldwide without having to depend on local bases for staging aircraft operations...
.Originally, Kaga was not going to be converted in favor of the two Amagi class. However, was severely damaged in the Great Kantō earthquake
1923 Great Kanto earthquake
The struck the Kantō plain on the Japanese main island of Honshū at 11:58:44 am JST on September 1, 1923. Varied accounts hold that the duration of the earthquake was between 4 and 10 minutes...
of 1923, so Kaga was converted instead. After having been converted into an aircraft carrier, Kaga took part in the attack on Pearl Harbor
Attack on Pearl Harbor
The attack on Pearl Harbor was a surprise military strike conducted by the Imperial Japanese Navy against the United States naval base at Pearl Harbor, Hawaii, on the morning of December 7, 1941...
, before eventually being sunk at the Battle of Midway
Battle of Midway
The Battle of Midway is widely regarded as the most important naval battle of the Pacific Campaign of World War II. Between 4 and 7 June 1942, approximately one month after the Battle of the Coral Sea and six months after Japan's attack on Pearl Harbor, the United States Navy decisively defeated...
in 1942.
Design
The Tosa class, designated as Design A-127 during early planning, was designed by Yuzuru HiragaYuzuru Hiraga
- External links :...
, who also had taken a lead role in the design of the s.
Dimensions and machinery
The ships had a planned displacement of 39900 LT (40,540.4 t), and 44200 LT (44,909.4 t) at a full load. They would have been 715 feet (217.9 m) long at the waterline, and 760 feet (231.6 m) overall; they would have had a beamBeam (nautical)
The beam of a ship is its width at the widest point. Generally speaking, the wider the beam of a ship , the more initial stability it has, at expense of reserve stability in the event of a capsize, where more energy is required to right the vessel from its inverted position...
of 100 feet (30.5 m) and a draft
Draft (hull)
The draft of a ship's hull is the vertical distance between the waterline and the bottom of the hull , with the thickness of the hull included; in the case of not being included the draft outline would be obtained...
of 30 in 10 in (9.4 m). Although a turbo-electric
Turbo-electric
A turbo-electric transmission uses electric generators to convert the mechanical energy of a turbine into electric energy and electric motors to convert it back into mechanical energy to power the driveshafts....
drive was considered for these ships after the United States announced that the plant was a great success in the battleship (the Japanese estimated that a 70000 shp turbo-electric plant could be installed in the Tosa class, which would have given the ships a speed of 25.25 kn (30.7 mph; 49.5 km/h), a 2500 nmi (2,877 mi; 4,630 km) range at full speed, and a 7800 nmi (8,976.1 mi; 14,445.6 km) range at 14 knots, it was rejected, and more conventional Curtis turbines
Steam turbine
A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....
were chosen. These turbines would have used 4 propeller shafts, and would have been powered by 12 Kampon water-tube boiler
Water-tube boiler
A water tube boiler is a type of boiler in which water circulates in tubes heated externally by the fire. Fuel is burned inside the furnace, creating hot gas which heats water in the steam-generating tubes...
s, 8 of which would have been oil fired, while the other 4 would have mixed oil and coal for fuel. This system would have provided 91000 shp for a top speed of 26.5 knots. The fuel stores would have amounted to 3,600 tons of oil and 1,800 tons of coal; at a speed of 14 knots, this would have enabled a maximum range of 6500 nmi (7,480.1 mi; 12,038 km).
Armament
The ships of the class were planned to be equipped with a main battery of ten 16 inches (406 mm) L/45L/45 denotes the length of the gun barrels; in this case, the gun is 45 calibers, meaning that the gun is 45 times long as it is in diameter. guns in five twin turretsGun turret
A gun turret is a weapon mount that protects the crew or mechanism of a projectile-firing weapon and at the same time lets the weapon be aimed and fired in many directions.The turret is also a rotating weapon platform...
. The guns fired 2205 lbs armor-piercing
Armor-piercing shot and shell
An armor-piercing shell is a type of ammunition designed to penetrate armor. From the 1860s to 1950s, a major application of armor-piercing projectiles was to defeat the thick armor carried on many warships. From the 1920s onwards, armor-piercing weapons were required for anti-tank missions...
projectile
Projectile
A projectile is any object projected into space by the exertion of a force. Although a thrown baseball is technically a projectile too, the term more commonly refers to a weapon....
s with a propellant
Propellant
A propellant is a material that produces pressurized gas that:* can be directed through a nozzle, thereby producing thrust ;...
charge weighing 494 lbs at 2592 feet per second (790 m/s), at a rate of fire between 1.5 to 2.5 rounds per minute. Each gun had 90 rounds, and had an approximate barrel life of 250 to 300 shots. The turrets would have been arranged along the centerline: two superfiring turrets fore, and three in line aft of the superstructure. The gun turrets weighed 1004 long tons (1,020.1 MT), and allowed for depression down to −5° and elevation to 30°.
The secondary battery would have consisted of twenty 5.5 inches (139.7 mm) L/50 guns mounted in casemate
Casemate
A casemate, sometimes rendered casement, is a fortified gun emplacement or armored structure from which guns are fired. originally a vaulted chamber in a fortress.-Origin of the term:...
s along the center of the ship. These guns fired 83.8 lbs projectiles and used between 22.8 lbs of propellant at a muzzle velocity
Muzzle velocity
Muzzle velocity is the speed a projectile has at the moment it leaves the muzzle of the gun. Muzzle velocities range from approximately to in black powder muskets , to more than in modern rifles with high-performance cartridges such as the .220 Swift and .204 Ruger, all the way to for tank guns...
between 2789 and 2805 ft/s (850.1 and 855 m/s). The guns had a maximum elevation of 25°, which enabled a maximum range of 19140 yards. Four—later increased to six—4.7 inches (119.4 mm) L/45 anti-aircraft guns were to have been mounted amidships, along with eight 24 inches (609.6 mm) above-water torpedo tubes.
Armor
The ships would have been protected by a main beltBelt armor
Belt armor is a layer of heavy metal armor plated on to or within outer hulls of warships, typically on battleships, battlecruisers and cruisers, and on aircraft carriers converted from those types of ships....
of armor 11 inches (279.4 mm) thick, sloped at 15°. The belt armor was designed to be able to defeat 16 inches (406.4 mm) shells from a distance of 12000 –. The main battery turrets and barbettes would have had between 9 and 12 in (228.6 and 304.8 mm) of armor plating, and the conning tower
Conning tower
A conning tower is a raised platform on a ship or submarine, often armored, from which an officer can con the vessel; i.e., give directions to the helmsman. It is usually located as high on the ship as practical, to give the conning team good visibility....
would have had armor 14 inches (355.6 mm) thick. The decks would have been 4 inches (101.6 mm) thick. The Tosa-class battleships would have had a torpedo bulkhead
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...
3 inches (76.2 mm) thick, which connected at the top to a 1.5 inches (38.1 mm) splinter deck beneath the main deck.
Background
Experiences in the Russo-Japanese WarRusso-Japanese War
The Russo-Japanese War was "the first great war of the 20th century." It grew out of rival imperial ambitions of the Russian Empire and Japanese Empire over Manchuria and Korea...
convinced naval war planners that more fast capital ships were needed, so on 4 April 1907, the Imperial Defence Council approved an "Eight-Eight
Eight-eight fleet
The was a Japanese naval strategy formulated for the development of the Imperial Japanese Navy in the first quarter of the 20th century, which laid down that the Japanese navy should include eight first-class battleships and eight armoured cruisers or battlecruisers.-History and development:The...
" policy. This plan originally called for a fleet of eight battleship
Battleship
A battleship is a large armored warship with a main battery consisting of heavy caliber guns. Battleships were larger, better armed and armored than cruisers and destroyers. As the largest armed ships in a fleet, battleships were used to attain command of the sea and represented the apex of a...
s and eight armored cruiser
Armored cruiser
The armored cruiser was a type of warship of the late 19th and early 20th centuries. Like other types of cruiser, the armored cruiser was a long-range, independent warship, capable of defeating any ship apart from a battleship, and fast enough to outrun any battleships it encountered.The first...
s that would all be under ten years old (later changed to eight battlecruiser
Battlecruiser
Battlecruisers were large capital ships built in the first half of the 20th century. They were developed in the first decade of the century as the successor to the armoured cruiser, but their evolution was more closely linked to that of the dreadnought battleship...
s and reduced to eight years old). However, the advent of the dreadnought
Dreadnought
The dreadnought was the predominant type of 20th-century battleship. The first of the kind, the Royal Navy's had such an impact when launched in 1906 that similar battleships built after her were referred to as "dreadnoughts", and earlier battleships became known as pre-dreadnoughts...
crippled this plan at the beginning; given Japan's economy and the enormous strain that had been put on it during the Russo-Japanese War (Japan emerged from the war victorious, but bankrupt), the launch of HMS Dreadnought
HMS Dreadnought (1906)
HMS Dreadnought was a battleship of the British Royal Navy that revolutionised naval power. Her entry into service in 1906 represented such a marked advance in naval technology that her name came to be associated with an entire generation of battleships, the "dreadnoughts", as well as the class of...
was a "disaster" for Japan.
In 1907, Japan was nominally halfway to the eight-eight with two newly-delivered pre-dreadnought
Pre-dreadnought
Pre-dreadnought battleship is the general term for all of the types of sea-going battleships built between the mid-1890s and 1905. Pre-dreadnoughts replaced the ironclad warships of the 1870s and 1880s...
battleships (the ) in the fleet and two more pre-dreadnoughts (the ) and four armored cruisers authorized or under construction. In addition, three more battleships and four armored cruisers had been authorized, though not funded. However, naval technology was changing; armored cruisers were seemingly obsolete in the face of the new battlecruisers being laid down by Great Britain and Germany. The Imperial Japanese Navy recognized this, and so they proposed in 1909 that two battlecruisers be ordered from British plans, with one to be built in Great Britain and one to be built at home. These two ships became the .
In 1910, there was still authorization for one battleship and four armored cruisers. This battleship, the battleship version of the Kongo-class battlecruisers, became Japan's first super-dreadnought Fuso
Japanese battleship Fuso
The Japanese battleship Fusō , was a part of the Imperial Japanese Navy, the lead ship of the Fusō-class. She was laid down by the Kure Kaigun Koshō on 11 March 1912, launched on 28 March 1914 and completed on 18 November 1915...
. With these ships, Japan appeared to be getting closer to the eight-eight goal; however, these new ships represented a "new level of naval strength" for the IJN, and they made all previous Japanese capital ship obsolete. This meant that any naval planner aiming for an eight-eight fleet would have to call for seven more battleships and four more battlecruisers when Japan was trying to weather a world economic depression.
After proposals from the IJN in 1911 and 1912 for massive shipbuilding programs, the Cabinet compromised down to a "four-four" plan; under this, three new battleships and no new battlecruisers were authorized. However, the Navy did not agree, and instead called for an "eight-four" fleet, while the Imperial Defence Council called for the original eight-eight. The Cabinet relented, and by July 1914, it was decided to go first for an eight-four fleet, followed by the eight-eight fleet. The eight-four plan was presented to the Diet
Diet of Japan
The is Japan's bicameral legislature. It is composed of a lower house, called the House of Representatives, and an upper house, called the House of Councillors. Both houses of the Diet are directly elected under a parallel voting system. In addition to passing laws, the Diet is formally...
in 1915; it planned to have the eight battleships and four battlecruisers by 1923 with the building of two and two Tosa-class battleships.
Construction, cancellation and fates
Mitsubishi
The Mitsubishi Group , Mitsubishi Group of Companies, or Mitsubishi Companies is a Japanese multinational conglomerate company that consists of a range of autonomous businesses which share the Mitsubishi brand, trademark and legacy...
shipyard in Nagasaki, and Kaga following on 19 July 1920 at the Kawasaki
Kawasaki Shipbuilding Corporation
-External links:*...
shipyard in Kobe. Both were launched less than two years after they were laid down; Tosa on 18 December 1921 and Kaga on 17 November 1921. Even though Tosa was laid down first, she was scheduled to be completed in March 1923 while Kagas planned completion date was 25 December 1922. However, the 1922 Washington Naval Treaty
Washington Naval Treaty
The Washington Naval Treaty, also known as the Five-Power Treaty, was an attempt to cap and limit, and "prevent 'further' costly escalation" of the naval arms race that had begun after World War I between various International powers, each of which had significant naval fleets. The treaty was...
intervened; this mandated the cancellation of all naval ships under construction, including the two Tosa class battleships; construction stopped on both ships on 5 February 1922. After being stricken on 1 April 1924, Tosa was expended as a target
Target ship
A target ship is a vessel — typically an obsolete or captured warship — used for naval gunnery practice or for weapons testing.-Rationale:Sinking redundant warships is an effective way of testing new weapons and warships in as realistic a manner as possible. Whilst practice torpedoes are fired...
in the Bungo Channel
Bungo Channel
The is a strait separating the Japanese islands of Kyūshū and Shikoku. It connects the Pacific Ocean and Seto Inland Sea. The narrowest part of this channel is the Hōyo Strait....
s on 9 February 1925; she was used as practice for naval gunfire and to test her armor scheme against mines and torpedoes. Accounts of these tests mention that shells struck the ship below the waterline, which could explain later IJN interest in internal armor; the results from all of these tests was used to design the protection of the s.
It was originally planned that Kaga would be scrapped. However, , one of the two battlecruisers which were being converted to aircraft carrier
Aircraft carrier
An aircraft carrier is a warship designed with a primary mission of deploying and recovering aircraft, acting as a seagoing airbase. Aircraft carriers thus allow a naval force to project air power worldwide without having to depend on local bases for staging aircraft operations...
s, was severely damaged in the Great Kantō earthquake
1923 Great Kanto earthquake
The struck the Kantō plain on the Japanese main island of Honshū at 11:58:44 am JST on September 1, 1923. Varied accounts hold that the duration of the earthquake was between 4 and 10 minutes...
in 1923 and rendered unusable. This meant that her conversion under the terms of the treatySee: Washington Naval Treaty, Chapter I, Article IX was impossible, so Kaga was reordered as a carrier in her stead; the conversion took 5 years (1923–28).
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
, although the actual figure was likely closer to 30,000 t; she was capable of steaming for 8000 nautical miles (14,816 km) when going 14 knots, though she was able to go at a maximum of 27.5 knots if needed. Similar to the former Amagi class carrier , Kaga was fitted with two flying-off decks "stepped down" from a flight deck that extended two-thirds of the ship; in theory, this allowed planes to take off directly from the hangars while other planes landed on the top. However, because operations proved dangerous and were impossible to conduct in rough weather, a 1935 reconstruction removed the lower two decks and extended the top flight deck to the bow.
After the reconstruction, Kaga officially displaced 38200 t (37,596.6 LT; 42,108.3 ST) standard; better boilers allowed her to obtain a top speed of around 28 knots, and the aircraft capacity was raised to 90. Interestingly, the ten 8-inch guns, although now all mounted singly in casemates, were retained. After supporting operations in China, Kaga took part in the attack on Pearl Harbor
Attack on Pearl Harbor
The attack on Pearl Harbor was a surprise military strike conducted by the Imperial Japanese Navy against the United States naval base at Pearl Harbor, Hawaii, on the morning of December 7, 1941...
on 7 December 1941. She covered amphibious assaults for the first three months of 1942, although she hit a reef in February. After receiving repairs for that damage in April, she sailed to support the landings on Midway; however, the IJN was surprised by the appearance of three U.S. carriers, beginning the Battle of Midway
Battle of Midway
The Battle of Midway is widely regarded as the most important naval battle of the Pacific Campaign of World War II. Between 4 and 7 June 1942, approximately one month after the Battle of the Coral Sea and six months after Japan's attack on Pearl Harbor, the United States Navy decisively defeated...
. Due in part to Admiral Isoroku Yamamoto's
Isoroku Yamamoto
was a Japanese Naval Marshal General and the commander-in-chief of the Combined Fleet during World War II, a graduate of the Imperial Japanese Naval Academy and a student of Harvard University ....
plan, in which ships were dispersed and not close enough to mutually support one another, Kaga, along with the other three carriers present, were sunk by U.S. aircraft from , and .