Tosa-class battleship

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Scale model of Kaga as originally designed
Class overview
NameTosa class
Builders
Operators Imperial Japanese Navy
Preceded byNagato class
Succeeded byKii class
Built1920–1922
Planned2
Completed1 converted to an aircraft carrier (Kaga)
Cancelled1
General characteristics
TypeDreadnought battleship
Displacement
  • 39,900 t (39,300 long tons) (normal)
  • 44,200 t (43,500 long tons) (
    full load
    )
Length234.09 m (768 ft)
Beam30.5 m (100 ft 1 in)
Draft9.4 m (30 ft 10 in)
Installed power
Propulsion4 × shafts; 4 × geared steam turbines
Speed26.5 knots (49.1 km/h; 30.5 mph)
Range5,500 nmi (10,200 km; 6,300 mi) at 16 knots (30 km/h; 18 mph)
Armament
Armor

The Tosa-class battleships (土佐型戦艦, Tosa-gata Senkan)

Eight-Eight" fleet for the Imperial Japanese Navy (IJN) during the early 1920s. The ships were larger versions of the preceding Nagato class, and carried an additional 41-centimeter (16.1 in) twin-gun turret. The design for the class served as a basis for the Amagi-class
battlecruisers.

Both ships were launched in late 1921, but the first ship,

scuttled in the Bungo Channel. The hull of the second ship, Kaga, was converted into an aircraft carrier of the same name. The carrier supported Japanese troops in China during the Second Sino-Japanese War of the late 1930s, and took part in the attack on Pearl Harbor on 7 December 1941 and the invasion of Rabaul in the Southwest Pacific in January 1942. The following month her aircraft participated in a combined carrier airstrike on Darwin, Australia, during the Dutch East Indies campaign. She was sunk during the Battle of Midway
in 1942.

Background

See also:
Fleet faction

The IJN believed that a modern battle fleet of eight battleships and eight

Diet rejected the plan and authorized only the dreadnought Nagato and two battlecruisers in the 1916 budget. Later that year American President Woodrow Wilson announced plans for ten additional battleships and six battlecruisers, and the Diet authorized three more dreadnoughts in response the following year: a second Nagato-class battleship—Mutsu—and two to a modified design, Tosa and Kaga.[3]

Design and description

The IJN began reevaluating the Nagato design in light of lessons learned from the

naval architect in charge of the fundamental design of the ships of the Eight-Eight Fleet, presented a heavily modified version of the Nagato design, A-125, to be built in lieu of the second ship of the class, Mutsu, on 12 June 1917, well before she was actually laid down.[4]

Hiraga's design for the ship reflected the latest combat experience as well as incorporating advances in

Navy Ministry.[5] The rejected design formed the basis for a much larger 39,000-metric-ton (38,000-long-ton) battleship, designated as A-127, with nearly twice as much armor weight as the Nagatos. It was designed to achieve the same speed as the older ships, to allow them to maneuver together as a tactical formation. This design was accepted on 27 March 1918 and became the Tosa class.[6]

The Tosa-class ships had a planned

Kampon water-tube boilers, eight of which would have used fuel oil and four of which would have used a mixture of oil and coal. This system would have provided 91,000 shaft horsepower (68,000 kW) to four propeller shafts for a top speed of 26.5 knots (49.1 km/h; 30.5 mph). The fuel stores would have amounted to 3,600 long tons (3,700 t) of oil and 1,800 long tons (1,800 t) of coal; at a speed of 14 knots, this would have enabled a maximum range of 6,500 nautical miles (12,000 km; 7,500 mi).[8]

Armament

Kure, Japan

The Tosa-class ships were intended to be armed with a

superfiring fore and aft. Numbered one through five from front to rear, the hydraulically powered turrets had an elevation range of −2 to +35 degrees. The rate of fire for the guns was around two rounds per minute.[9] The ships were designed to carry 90 rounds per gun, although space was available for 110.[10]

The guns used Type 91

high-explosive shell that had a muzzle velocity of 805 meters per second (2,640 ft/s).[11]

The ships' secondary armament of twenty 50-caliber

AA guns in single mounts. The 3-inch (76 mm) high-angle guns had a maximum elevation of +75 degrees, and a rate of fire of 13 to 20 rounds per minute. They fired a 6 kg (13 lb) projectile with a muzzle velocity of 680 m/s (2,200 ft/s) to a maximum height of 7,500 meters (24,600 ft).[13] The guns were normally supplied with 250 rounds each, although space was available for a total of 400 rounds per gun.[10] These 3rd Year Type guns were intended to be replaced by four 45-caliber 12-centimeter (4.7 in) anti-aircraft guns.[8]

The Tosas were intended to mount eight 61-centimeter (24 in) torpedo tubes, four above water and four below. The former were to be provided with two torpedoes each and the latter with three each.[10]

Armor

The ships' armor protection was designed to break up 16-inch (406 mm) shells from a distance of 15,000–20,000 meters (16,000–22,000 yd) and the primary armor plates were backed up by splinter

Amidships it would have been 280 mm (11 in) thick and 254 mm (10 in) thick fore and aft. Approximately 1.83 meters (6 ft 0 in) of the armor belt was below the waterline. The side armor was closed off at its ends by bulkheads 229–254 mm (9–10 in) thick.[14] The main battery turrets and the portions of the barbettes above the main deck would have had between 229 and 305 mm (9.0 and 12.0 in) of armor plating,[8] and the conning tower walls would have had armor 254 and 356 mm (10.0 and 14.0 in) thick and a roof of 178 mm (7.0 in) armor plates. The communications tube below the conning tower would have had walls 76–127 mm (3.0–5.0 in) thick.[15]

The middle deck was the primary armored deck and was connected to the top of the armor belt. It would have consisted of a 63.5 mm (2.5 in) plate of New Vickers non-cemented armor on top of a 37 mm (1.5 in) plate of high-tensile steel (HTS) above the engine and boiler rooms. Above the magazines, the thickness of the HTS plate would have increased to 63 mm. The lower deck would have consisted of two 19 mm (0.75 in) plates of HTS. For the first time in a Japanese ship, the Tosas would have had the lower portion of the single funnel protected by 229 mm of armor. In addition, the funnel openings in the lower deck would have been protected by armor gratings.[14]

The ships would have had an internal

torpedo bulge to provide protection against underwater explosions. This was backed by a torpedo bulkhead also made up of three 25 mm (0.98 in) layers of HTS and angled outwards to meet the base of the waterline belt. It connected to a 12.7–32 mm (0.50–1.26 in) splinter bulkhead on the lower deck behind the waterline belt. Behind the torpedo bulge and the splinter bulkhead was another splinter bulkhead 12.7–19 mm thick.[16]

Ships

Construction data
Name Builder[8]
Laid down[8]
 Launched[8] Completion[8] Fate
Tosa (土佐) Mitsubishi Shipyard, Nagasaki 16 February 1920 18 December 1921 March 1923 (estimated)
Scuttled, 9 February 1925[17]
Kaga (加賀) Kawasaki Shipyard, Kobe 19 July 1920 17 November 1921 25 December 1922 Sunk during the Battle of Midway, 4 June 1942[18]

Cancellation and fates

Small tugboats surround a partially completed large ship; dark smoke is rising from the boats
Tosa, partly complete, being towed from Nagasaki in 1922

Construction of both ships began in 1920, but the 1922 Washington Naval Treaty intervened, mandating the cancellation of all capital ships being built. Work stopped on the two Tosa-class battleships on 5 February 1922.[19] After being stricken on 1 April 1924,[8] Tosa's guns were turned over to the Imperial Japanese Army for use as coastal artillery; two of her main-gun turrets were installed on Tsushima Island and near Busan, Korea.[20] The rest of her guns were placed in reserve and ultimately scrapped in 1943.[21] Tosa's incomplete hull was used to test her armor scheme against long-range naval gunfire, aerial bombs, mines, and torpedoes. Two of the shells fired at her fell short, but deeply penetrated her hull through the thin armor of the torpedo bulge below the waterline armor belt. This sparked an interest in optimizing underwater performance of Japanese shells that culminated in production of the Type 91 armor-piercing shell. Conversely, the IJN took measures to defend against shells of this type when reconstructing its existing battleships during the 1930s, as well as in the designs of the Yamato-class battleships and the heavy cruisers of the Mogami and Tone classes. Tosa's torpedo defense system proved able to defeat 200 kg (440 lb) torpedo warheads, but not larger 350 kg (770 lb) ones. After the conclusion of the tests, the ship was scuttled by opening her Kingston valves on 9 February 1925 in 650 m (2,130 ft) of water in the Bungo Channel after the demolition charges failed to detonate.[22]

The battlecruiser Amagi, which was being converted to an aircraft carrier under the terms of the treaty, was wrecked in the Great Kantō earthquake in 1923 and rendered unusable. As a result, Kaga, which was originally slated to be scrapped under the terms of the Washington Naval Treaty (Chapter I, Article IX),[8] was converted in Amagi's stead. No work took place until 1925 as new plans were drafted and earthquake damage to the Yokosuka Naval Arsenal was repaired. Although the ship was commissioned on 31 March 1928, she did not join the Combined Fleet (Rengō Kantai) until 30 November 1929.[23]

A crane in the background towers over the mostly completed ship
Kaga, seen from the stern, under construction in Yokosuka naval yard in November 1928; note the large pipe that directed exhaust smoke down, away from any landing aircraft

Much like the converted Amagi-class battlecruiser Akagi, 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. As aircraft became heavier during the 1930s, they required longer distances to get airborne and the lower flight decks became useless. Kaga's 1935 reconstruction removed the lower two decks and extended the top flight deck to the bow.[24] As completed, the ship had two main hangar decks and a third auxiliary hangar with a total capacity of 60 aircraft.[25]

Kaga was provided with a heavy gun armament in case she was surprised by enemy cruisers and forced to give battle, but her large and vulnerable flight deck, hangars, and other features made her more of a target in any surface action than a fighting warship. Carrier doctrine was still evolving at this time and the impracticability of carriers engaging in gun duels had not yet been realized.[26] The ship was armed with ten 20 cm/50 3rd Year Type guns: one twin-gun turret on each side of the middle flight deck and six in casemates aft. Kaga's waterline armored belt was reduced from 280 to 152 mm (11.0 to 6.0 in) during her reconstruction and her deck armor was also reduced from 102 to 38 mm (4.0 to 1.5 in). The carrier displaced 26,900 long tons (27,300 t) at standard load, and 33,693 long tons (34,234 t) at full load, nearly 6,000 long tons (6,100 t) less than her designed displacement as a battleship. This reduction in her displacement increased her speed to 27.5 knots (50.9 km/h; 31.6 mph) and gave her a range of 8,000 nautical miles (15,000 km; 9,200 mi) at 14 knots (26 km/h; 16 mph).[27]

Kaga after her 1930s reconstruction

In 1933–35 Kaga was rebuilt to increase her top speed, improve her exhaust systems, and adapt her flight decks to more modern, heavier aircraft. After the reconstruction, the ship displaced 38,200 long tons (38,800 t) at standard load, better boilers gave her a top speed of 28.3 knots (52.4 km/h; 32.6 mph), and additional fuel storage increased her range to 10,000 nautical miles (19,000 km; 12,000 mi) at 15 knots (28 km/h; 17 mph) and raised her aircraft capacity to 90. The ten 20 cm (7.9 in) guns, although now all mounted singly in casemates, were retained.[28]

Kaga's aircraft first supported Japanese troops in China during the

1st Air Fleet for the attack on Midway Atoll in June 1942.[30]

The IJN was surprised by the appearance of three American carriers and, partly due to Admiral Isoroku Yamamoto's plan in which ships were too dispersed to support each other, Kaga, along with the other three carriers present, was sunk by aircraft from USS Enterprise, Hornet and Yorktown on 4 June.[18]

Notes

  1. ^ The ships are sometimes referred to as the Kaga class, after the ship that was planned to have been completed first.
  2. 12-pounder guns. While the Japanese designated them as 8 cm, their actual caliber was 76.2 mm.[13]

Footnotes

  1. ^ Evans & Peattie, p. 150
  2. ^ Stille, p. 7
  3. ^ Evans & Peattie, pp. 160, 166–167
  4. ^ Lengerer 2010, pp. 3, 7
  5. ^ Lengerer 2010, pp. 3, 6–7
  6. ^ Lengerer 2010, pp. 4, 10
  7. ^ Lengerer 2010, pp. 11–12
  8. ^ a b c d e f g h i Gardiner & Gray, p. 232
  9. ^ Skwiot, p. 19
  10. ^ a b c d Lengerer 2010, p. 11
  11. ^ Campbell, pp. 181–182
  12. ^ Campbell, p. 190
  13. ^ a b Campbell, p. 198
  14. ^ a b Lengerer 2010, pp. 8–9
  15. ^ Lengerer 2010, p. 9
  16. ^ Lengerer 2010, p. 8
  17. ^ Lengerer 2010, p. 26
  18. ^
    Naval Historical Center
    . 6 April 1999. Retrieved 18 January 2009.
  19. ^ See: Washington Naval Treaty, Chapter II, Part III, Section II
  20. ^ Gibbs, p. 217
  21. ^ Gibbs & Tamura, p. 192
  22. ^ Lengerer 2010, pp. 18–22, 25–26
  23. ^ Lengerer 1982, p. 128
  24. ^ Lengerer 1982, pp. 130, 136
  25. ^ Peattie, p. 231
  26. ^ Peattie, pp. 53, 55
  27. ^ Lengerer 1982, pp. 129, 131, 134
  28. ^ Lengerer 1982, p. 134
  29. ^ Peattie, pp. 50–51, 103–104
  30. ^ Lengerer 1982, pp. 174–177

References

Further reading

External links

Media related to Tosa-class battleships at Wikimedia Commons

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