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17 November 1921 - Japanese aircraft carrier Kaga launched

Kaga (加賀) was an aircraft carrier built for the Imperial Japanese Navy (IJN) and was named after the former Kaga Province in present-day Ishikawa Prefecture. Originally intended to be one of two Tosa-class battleships, Kaga was converted under the terms of the Washington Naval Treaty to an aircraft carrier as the replacement for the battlecruiser Amagi, which had been damaged during the 1923 Great Kantō earthquake. Kaga was rebuilt in 1933–35, increasing her top speed, improving her exhaust systems, and adapting her flight decks to more modern, heavier aircraft.

The ship figured prominently in the development of the IJN's carrier striking force doctrine, which grouped carriers together to give greater mass and concentration to their air power. A revolutionary strategic concept at the time, the employment of the doctrine was crucial in enabling Japan to attain its initial strategic goals during the first six months of the Pacific War.

Imperial Japanese Navy Carrier Kaga: photo taken after her massive refitting. Its smokestack is directed downwards to extinguish the smoke with seawater.

Kaga's aircraft first supported Japanese troops in China during the Shanghai Incident of 1932 and participated in the Second Sino-Japanese War in the late 1930s. With other carriers, she took part in the Pearl Harbor raid in 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, helping secure the conquest of the Dutch East Indies by Japanese forces. She missed the Indian Ocean raid in April as she had to return to Japan for permanent repairs after hitting a reef in February.

Following repairs, Kaga rejoined the 1st Air Fleet for the Battle of Midway in June 1942. After bombarding American forces on Midway Atoll, Kaga and three other IJN carriers were attacked by American aircraft from Midway and the carriers Enterprise, Hornet, and Yorktown. Dive bombers from Enterprise severely damaged Kaga; when it became obvious she could not be saved, she was scuttled by Japanese destroyers to prevent her from falling into enemy hands. The loss of four large attack carriers, including Kaga at Midway, was a crucial setback for Japan, and contributed significantly to Japan's ultimate defeat. In 1999, debris from Kaga including a large section of the hull was located on the ocean floor at a depth in excess of 5,000 meters (16,404 ft); 350 miles (560 km) northwest of Midway Island. The main part of the carrier's wreck has not been found.

Design and construction
See also: Tosa-class battleship
Kaga was laid down as a Tosa-class battleship, and was launched on 17 November 1921 at the Kawasaki Heavy Industries shipyard in Kobe. On 5 February 1922 both Tosa-class ships were canceled and scheduled to be scrapped under the terms of the Washington Naval Treaty.

The Treaty authorized conversion of two battleship or battlecruiser hulls into aircraft carriers of up to 33,000 long tons (34,000 t) standard displacement. The incomplete battlecruisers Amagi and Akagi were initially selected, but the Great Kantō earthquake of 1923 damaged Amagi's hull beyond economically feasible repair, and Kaga was selected as her replacement. The formal decision to convert Kaga to an aircraft carrier was issued 13 December 1923, but no work took place until 1925 as new plans were drafted and earthquake damage to the Yokosuka Naval Arsenal was repaired. She was officially commissioned on 31 March 1928, but this signified only the beginning of sea trials. She joined the Combined Fleet (Rengō Kantai) on 30 November 1929 as the IJN's third carrier to enter service, after Hōshō (1922) and Akagi (1927).

Kaga was completed with a length of 238.5 meters (782 ft 6 in) overall. She had a beam of 31.67 meters (103 ft 11 in) and a draft at full load of 7.92 meters (26 ft 0 in). She 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. Her complement totaled 1340 crewmembers.

Flight deck arrangements

Kaga as completed, with all three flight decks visible

Kaga, like Akagi, was completed with three superimposed flight decks, the only carriers ever to be designed so. The British carriers converted from "large light cruisers", HMS Glorious, HMS Courageous, and HMS Furious, each had two flight decks, but there is no evidence that the Japanese copied the British model. It is more likely that it was a case of convergent evolution to improve launch and recovery cycle flexibility by allowing simultaneous launch and recovery of aircraft. Kaga's main flight deck was 171.2 meters (561 ft 8 in) long, her middle flight deck was only about 15 meters (49 ft 3 in) long and started in front of the bridge, and her lower flight deck was approximately 55 meters (180 ft 5 in) long. The utility of her middle flight deck was questionable as it was so short that only some of the lightly loaded aircraft could use it, even in an era when the aircraft were much lighter and smaller than they were during World War II. At any rate the ever-increasing growth in aircraft performance, size and weight during the 1930s meant that even the bottom flight deck was no longer able to accommodate the take-off roll required for the new generations of aircraft being fielded and it was plated over when the ship was modernized in the mid-1930s. Kaga's main flight deck was completely flat until a conning tower was added during the modernization.

As completed, the ship had two main hangar decks and a third auxiliary hangar with a total capacity of 60 aircraft. The hangars opened onto the middle and lower flight decks to allow aircraft to take off directly from the hangars while landing operations were in progress on the main flight deck above. No catapults were fitted. Her forward aircraft lift was offset to starboard and 10.67 by 15.85 meters (35.0 by 52.0 ft) in size. Her aft lift was on the centerline and 12.8 by 9.15 meters (42 ft 0 in by 30 ft 0 in). Her arresting gear was a French transverse system as used on their aircraft carrier Béarn and known as the Model Fju (Fju shiki) in the Japanese service.

As originally completed, Kaga carried an air group of 28 Mitsubishi B1M3 torpedo bombers, 16 Nakajima A1N fighters and 16 Mitsubishi 2MR reconnaissance aircraft.

Armament and armor

Kaga's fitting-out in 1928. This stern view shows the long funnel extending aft below the flight deck, and three 8-inch (200 mm) guns in casemates.

Kaga was armed with ten 20 cm/50 3rd Year Type guns: one twin-gun Model B turret on each side of the middle flight deck and six in casemates aft. They fired 110-kilogram (240 lb) projectiles at a rate of three to six rounds per minute with a muzzle velocity of 870 m/s (2,900 ft/s); at 25°, they had a maximum range between 22,600 and 24,000 m (24,700 and 26,200 yd). The Model B turrets were nominally capable of 70° elevation to provide additional anti-aircraft (AA) fire, but in practice the maximum elevation was only 55°. The slow rate of fire and the fixed 5° loading angle minimized any real anti-aircraft capability. This heavy gun armament was provided 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.

She was given an anti-aircraft armament of six twin 12-centimeter (4.7 in) 45-caliber 10th Year Type Model A2 gun mounts fitted on sponsons below the level of the funnels, where they could not fire across the flight deck, three mounts per side. These guns fired 20.3-kilogram (45 lb) projectiles at a muzzle velocity of 825–830 m/s (2,707–2,723 ft/s); at 45° this provided a maximum range of 16,000 meters (17,000 yd), and they had a maximum ceiling of 10,000 meters (33,000 ft) at 75° elevation. Their effective rate of fire was 6 to 8 rounds per minute. She had two Type 89 directors to control her 20 cm guns and two Type 91 manually powered anti-aircraft directors (Kōshaki) to control her 12 cm guns.

Kaga's waterline armored belt was reduced from 280 to 152 mm (11.0 to 6.0 in) during her reconstruction and the upper part of her torpedo bulge was given 127 mm (5.0 in) of armor. Her deck armor was also reduced from 102 to 38 mm (4.0 to 1.5 in).

Propulsion

Kaga undergoing post-launch trials off Tateyama, 15 September 1928.

Kaga conducting air operations in 1930. On the upper deck are Mitsubishi B1M torpedo bombers preparing for takeoff. Nakajima A1N Type 3 fighters are parked on the lower deck forward.

When Kaga was being designed, the problem of how to deal with exhaust gases in carrier operations had not been resolved. The swiveling funnels of Hōshō had not proved successful and wind-tunnel testing had not provided an answer. As a result, Akagi and Kaga were given different exhaust systems to evaluate in real-world conditions. Kaga's funnel gases were collected in a pair of long horizontal ducts which discharged at the rear of each side of the flight deck, in spite of predictions by a number of prominent naval architects that they would not keep the hot gases away from the flight deck. The predictions proved to be correct, not least because Kaga was slower than the Akagi which allowed the gases to rise and interfere with landing operations. Another drawback was that the heat of the gases made the crew's quarters located on the side of the ship by the funnels almost uninhabitable.

Kaga was completed with four Kawasaki Brown-Curtis geared turbines with a total of 91,000 shaft horsepower (68,000 kW) on four shafts. As a battleship her expected speed had been 26.5 knots (49.1 km/h; 30.5 mph), but the reduction in displacement from 39,900 to 33,693 long tons (40,540 to 34,234 t) allowed this to increase to 27.5 knots (50.9 km/h; 31.6 mph), as demonstrated on her sea trials on 15 September 1928. She had twelve Kampon Type B (Ro) boilers with a working pressure of 20 kg/cm2 (2,000 kPa; 280 psi), although only eight were oil-fired. The other four used a mix of oil and coal. She carried 8,000 long tons (8,128 t) of fuel oil and 1,700 long tons (1,727 t) of coal to give her a range of 8,000 nautical miles (15,000 km; 9,200 mi) at 14 knots (26 km/h; 16 mph).

Reconstruction
During her second reconstruction Kaga's two lower flight decks were converted into hangars and, along with the main flight deck, were extended to the bow. This increased the flight deck length to 248.55 meters (815 ft 5 in) and raised aircraft capacity to 90 (72 operational and 18 in storage). A third elevator forward, 11.5 by 12 meters (37 ft 9 in × 39 ft 4 in), serviced the extended hangars. Bomb and torpedo elevators were modified to deliver their munitions directly to the flight deck. Her arrester gear was replaced by a Japanese-designed Type 1 system. A small starboard island superstructure was also installed.

Kaga after reconstruction showing the new, full-length flight deck above the wide battleship hull.

Her power plant was completely replaced as were her propellers. New Kampon multi-stage geared turbines were fitted that increased her power from 91,000 to 127,400 shp (67,859 to 95,002 kW) during trials. Each had a high-pressure, a low-pressure, and a cruising turbine coupled to a single shaft. Her boilers were replaced by eight improved oil-burning models of the Kampon Type B (Ro) with a working pressure of 22 kg/cm2 (2,157 kPa; 313 psi) at a temperature of 300 °C (572 °F). The hull was lengthened by 10.3 meters (33 ft 10 in) at the stern to reduce drag and she was given another torpedo bulge above the side armor abreast the upper part of the existing bulge to increase her beam and lower her center of gravity as a result of lessons learned from the Tomozuru Incident in early 1934. This raised her standard displacement significantly, from 26,900 to 38,200 long tons (27,332 to 38,813 t). The extra power and the extra displacement roughly offset each other and her speed increased by less than a knot, up to 28.34 knots (52.49 km/h; 32.61 mph) on trials. Her fuel storage was increased to 7,500 long tons (7,620 t) of fuel oil which increased her endurance to 10,000 nmi (18,520 km; 11,510 mi) at 16 knots (30 km/h; 18 mph). The lengthy funnel ducting was replaced by a single downturned starboard funnel modeled on that used by the Akagiwith a water-cooling system for the exhaust gasses and a cover that could be raised to allow the exhaust gasses to escape if the ship developed a severe list and the mouth of the funnel touched the sea. The space freed up by the removal of the funnel ducts was divided into two decks and converted into living quarters for the expanded air group. The carrier's complement increased to 1708 crewmembers.

The two twin turrets on the middle flight deck were removed and four new 20 cm/50 3rd Year Type No. 1 guns in casemates were added forward. Her 12 cm anti-aircraft guns were replaced by eight 12.7-centimeter (5.0 in)/40 Type 89 guns in twin mounts. They fired 23.45-kilogram (51.7 lb) projectiles at a rate between 8 and 14 rounds per minute at a muzzle velocity of 700–725 m/s (2,300–2,380 ft/s); at 45°, this provided a maximum range of 14,800 meters (16,200 yd), and a maximum ceiling of 9,400 meters (30,800 ft). Their sponsons were raised one deck to allow them some measure of cross-deck fire. Eleven twin 25 mm Type 96 gun mounts were added, also on sponsons. They fired .25-kilogram (0.55 lb) projectiles at a muzzle velocity of 900 m/s (3,000 ft/s); at 50°, this provided a maximum range of 7,500 meters (8,202 yd), and an effective ceiling of 5,500 meters (18,000 ft). The maximum effective rate of fire was only between 110 and 120 rounds per minute due to the frequent need to change the fifteen-round magazines. Six 6.5-millimeter (0.26 in) Type 11 machine guns were also carried.[29] Six Type 95 directors were fitted to control the new 25 mm guns, but Kaga retained her outdated Type 91 anti-aircraft directors.

Several major weaknesses in Kaga's design were not rectified. Kaga's aviation fuel tanks were incorporated directly into the structure of the carrier, meaning that shocks to the ship, such as those caused by bomb or shell hits, would be transmitted directly to the tanks, resulting in cracks or leaks. Also, the fully enclosed structure of the new hangar decks made fire suppression difficult, at least in part because fuel vapors could accumulate in the hangars. Adding to the danger was the requirement from the Japanese carrier doctrine that aircraft be serviced, fueled, and armed whenever possible on the hangar decks rather than on the flight deck. In addition, the carrier's hangar and flight decks carried little armor protection. Furthermore, there was no redundancy in the ship's fire-extinguishing systems. These weaknesses would later be crucial factors in the loss of the ship.

Read about her career at wikipedia.....

http://en.wikipedia.org/wiki/Japanese_aircraft_carrier_Kaga