Japanese aircraft carrier Kaga

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.[3]

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).[4]

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). 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.[5] Her complement totaled 1,340 crewmembers.[6]

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", Glorious, Courageous, and 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.[7] Kaga's main flight deck was 171.2 meters (561 ft 8 in) long and 30.5 meters (100 ft) wide,[8] 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.[9] 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.[10] Kaga lacked an island until one was added during the modernization.[11]

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.[12] Her forward aircraft elevator was offset to starboard and 10.67 by 15.85 meters (35 by 52 ft) in size. Her aft elevator was on the centerline and 12.8 by 9.15 meters (42 by 30 ft). 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.[13] As originally completed, Kaga carried an air group of 28 Mitsubishi B1M3 torpedo bombers, 16 Nakajima A1N fighters and 16 Mitsubishi 2MR reconnaissance aircraft.[5][Note 1]

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 (7.9 in) 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.[14] 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.[15][Note 2]

She was given an anti-aircraft armament of six twin 12-centimeter (4.7 in) 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.[16] 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.[17] 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.[18] Kaga's waterline armored belt was reduced from 280 to 152 mm (11 to 6 in) during her reconstruction and the upper part of her torpedo bulge was given 127 mm (5 in) of armor. Her deck armor was also reduced from 102 to 38 mm (4 to 1 in).[13]

Propulsion

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

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 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.[13]

Kaga was completed with four Kawasaki Brown-Curtis geared steam 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).[13]

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.

On 1 December 1931 Kaga was assigned as the flagship of the First Carrier Division under the command of Rear Admiral Takayoshi Katō.[19] The First Carrier Division, along with Hōshō, departed for Chinese waters on 29 January 1932 to support Imperial Japanese Army troops during the Shanghai Incident as part of the IJN's 3rd Fleet.[20] The B1M3s carried by Kaga and Hōshō were the main bombers used during the brief combat over Shanghai.[21]

Ikuta, Kuroiwa, and Takeo pose in front of a Nakajima A1N2 Type 3

Kaga's aircraft, operating from both the carrier and a temporary base at Kunda Airfield in Shanghai, flew missions in support of Japanese ground forces throughout February 1932. During one of these missions three of Kaga's Nakajima A1N2 fighters, including one piloted by future ace Toshio Kuroiwa, escorting three Mitsubishi B1M3 torpedo bombers, scored the IJN's first air-to-air combat victory on 22 February when they shot down a Boeing P-12 flown by an American volunteer pilot.[19][22] Kaga returned to home waters upon the declaration of the cease-fire on 3 March and resumed fleet training with the rest of the Combined Fleet.[19]

At this time, the IJN's developing carrier doctrine was still in its earliest stages. Kaga and the other carriers were initially given roles as tactical force multipliers supporting the fleet's battleships in the IJN's "decisive battle" doctrine. In this role, Kaga's aircraft were to attack enemy battleships with bombs and torpedoes. Aerial strikes against enemy carriers were later, beginning around 1932–1933, deemed of equal importance in order to establish air superiority during the initial stages of battle. The essential component in this strategy was that the Japanese carrier aircraft must be able to strike first with a massed aerial attack. As a result, in fleet training exercises the carriers began to operate together in front of or with the main battle line. This revolutionary strategy emphasized maximum speed from both the carriers and the aircraft they carried as well as larger aircraft with greater range. Thus, longer flight decks on the carriers were required in order to handle the newer, heavier aircraft which were entering service.[23]

Kaga was soon judged inferior to Akagi because of her slower speed, smaller flight deck (64 feet (19.5 m) shorter), and problematic funnel arrangement. Because of Kaga's perceived limitations, she was given priority over Akagi for modernization.[24] Kaga was relegated to reserve status on 20 October 1933 to begin a second major reconstruction, with an official start date of 25 June 1934.[20]

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).[25] A third elevator forward, 11.5 by 12 meters (37 ft 9 in × 39 ft 4 in), serviced the extended hangars.[5] 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.[12]

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. Kaga was equipped with 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). 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. 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 (19,000 km; 12,000 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 Akagi with 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.[26] The carrier's complement increased to 1708 crewmembers.[27]

The two twin turrets on the middle flight deck were removed and four new 20 cm 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) 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).[28] 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 0.25-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.[29] Six 6.5-millimeter (0.26 in) Type 11 machine guns were also carried.[26] Six Type 95 directors were fitted to control the new 25 mm guns, but Kaga retained her outdated Type 91 anti-aircraft directors.[27]

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.[30]

Kaga returned to service in 1935 and was assigned to the Second Carrier Division. The carrier embarked a new set of aircraft, including 16 Nakajima A2N Type 90 fighters, 16 Aichi D1A Type 94/96 dive bombers, and 28 Mitsubishi B2M Type 89 torpedo bombers.[31]

Kaga conducts air operations in 1937; on deck are Nakajima A2N, Aichi D1A, and Mitsubishi B2M aircraft

The renewal of hostilities with China at the Marco Polo Bridge in July 1937 found Kaga in home waters. The ship's fighter squadron completed training at Ōmura, Nagasaki then helped escort ships taking army reinforcements from Japan to China. On 15 August, along with Hōshō and Ryūjō, the ship took station in the East China Sea as part of the 3rd Fleet and began supporting Japanese military operations along the central China coast around Shanghai and further inland.[32][33]

Kaga aircraft fought their first battle on 15 August 1937, when thirteen Aichi D1A1 (Type 94) dive-bombers encountered Chinese Air Force Curtiss A-12 Shrike attack-bombers of the 26th and 27th Squadrons at Chao'er Airbase preparing for strikes against Japanese positions in Shanghai, and a dogfight duly ensued between the two unlikely dogfighting opponents; two D1A1s were shot down; a third badly shot-up D1A1 returned to Kaga with a fatally wounded crewman, while the D1A1 flight claimed three Shrikes.[34] On 16 August 1937, six Type 90 fighters engaged four Chinese aircraft over Kiangwan, shooting down three without loss. Between 17 August and 7 September, Kaga's Type 90 and two Mitsubishi A5M Type 96 fighters, which joined the carrier on 22 August, engaged Chinese aircraft on several more occasions. Kaga's fighter pilots claimed to have shot down 10 Chinese aircraft in these encounters without loss.[35] On 17 August twelve of the carrier's bombers attacked Hangchow without fighter escort and 11 of them were shot down by Chinese fighters.[36] On 7 September, three Type 96 (A5M) fighters escorted six Type 96 (D1A2) bombers and were engaged by three Chinese Hawk IIIs near Taihu Lake; two Type 96 bombers were quickly shot down, but the ensuing half-hour long dogfight resulted in no further losses for either side despite claims.[37] Beginning on 15 September, six Type 90 and six Type 96 fighters, 18 dive bombers, and 18 torpedo bombers were temporarily deployed to Kunda Airfield from the ship to support land operations.[38]

A Japanese Type 96 attack plane flies near Kaga during the China incident

On 26 September the carrier went to Sasebo for reprovisioning. At Sasebo, the carrier received new replacement aircraft including 32 Yokosuka B4Y Type 96 carrier attack planes (torpedo bombers), 16 Aichi D1A2 Type 96 carrier bombers (dive bombers), and 16 more Type 96 fighters. Several Nakajima A4N Type 95 fighter aircraft augmented the carrier's fighter group at an unspecified later date.[38]

Kaga returned to the front in early October 1937, and except for two brief trips to Sasebo, remained off China until December 1938. Using Taiwan (then part of the Empire of Japan) as its base, the carrier steamed 29,048 nautical miles (53,797 km; 33,428 mi) supporting military operations from the South and East China Seas. During that time, Kaga bombers supported army operations by attacking enemy railroad bridges, airfields, and transportation vehicles. The carrier's fighter pilots claimed to have destroyed at least 17 Chinese aircraft in aerial combat while losing five aircraft themselves. On 12 December 1937 Kaga aircraft participated in the Panay incident.[39]

On 11 November 1937, three Chinese Air Force Northrop Gamma 2ECs of the 2nd BG, 14th Squadron led by Captain Yu Y.C. attacked Kaga off the Maanshan Islands near Shanghai; the bombs fell wide into Kaga's wake, and the Chinese Gammas were pursued and intercepted by three A5Ms of Kaga's combat air patrol (CAP) led by flight leader Jirō Chōno, which shot down two of the Gammas, while Yu managed to escape into the clouds and return to base in his damaged Gamma.[40]

Six Kaga fighters were assigned to land bases near Shanghai and Nanking between 9 December 1937 and 15 January 1938. Nine fighters were temporarily based out of Nanking from 3 March through 4 April 1938. On 13 April 1938, Kaga launched eighteen D1A1s and three each of A4Ns and A5Ms on a strike against Canton, and they were met by two squadrons of Gloster Gladiators of the 5th Fighter Group led by Captain John Xinrui Huang and Captain Louie Yim-qun; Huang would score a triple kill in this battle against the Kaga raid, while Jirō Chōno (A5M) and Hatsuo Hidaka (A4N) would each claim double kills, including Chōno's shooting-down of Huang, who was injured bailing out.[41] Kaga's fighter group at this time included future aces Jirō Chōno, Osamu Kudō, Yoshio Fukui, Watari Handa, Masaichi Kondō, Hatsuo Hidaka, Kiichi Oda, Satoru Ono, and Chitoshi Isozaki.[42] The US Navy decrypted an IJN message which reportedly indicated that the attack on the Panay and other neutral ships in the Yangtze River had been knowingly and deliberately planned by an air officer on Kaga.[43]

Kaga entered the shipyard on 15 December 1938, where her arresting gear was replaced by a Type 3 system and her bridge was modernized. The flight deck and hangar areas were enlarged, increasing the carrier's aircraft capacity. The ship was completely overhauled from 15 November 1939 to 15 November 1940 before returning to active service. In the meantime, a new generation of aircraft had entered service and Kaga embarked 12 A5M fighters, 24 D1A dive bombers and 36 B4Y torpedo bombers. Another 18 aircraft were carried in crates as spares.[20][44][Note 3]

The Japanese carriers' experiences off China had helped further develop the IJN's carrier doctrine. One lesson learned in China was the importance of concentration and mass in projecting naval air power ashore. Therefore, in April 1941 the IJN formed the First Air Fleet to combine all of its fleet carriers under a single command. On 10 April 1941 Kaga was assigned to the First Carrier Division with Akagi as part of the new carrier fleet, which also included the Second and Fifth carrier divisions. The IJN centered its doctrine on airstrikes that combined the air groups within carrier divisions, rather than each individual carrier. When more than one carrier division was operating together, the divisions' air groups were combined with each other. This doctrine of combined, massed, carrier air attack groups was the most advanced of its kind of all the world's navies. The IJN, however, remained concerned that concentrating all of its carriers together would render them vulnerable to being wiped out all at once by a massive enemy air or surface strike. Thus, the IJN developed a compromise solution in which the fleet carriers would operate closely together within their carrier divisions but the divisions themselves would operate in loose rectangular formations, with approximately 7,000 metres (7,700 yd) separating the carriers from each other.[45][Note 4]

Although the concentration of so many fleet carriers into a single unit was a new and revolutionary offensive strategic concept, the First Air Fleet suffered from several defensive deficiencies which gave it, in Mark Peattie's words, a "'glass jaw': it could throw a punch but couldn't take one."[46] Japanese carrier anti-aircraft guns and associated fire control systems had several design and configuration deficiencies which limited their effectiveness. The IJN's fleet CAP consisted of too few fighter aircraft and was hampered by an inadequate early warning system, including a lack of radar. Poor radio communications with the fighter aircraft inhibited effective command and control of the CAP. The carriers' escorting warships were deployed as visual scouts in a ring at long range, not as close anti-aircraft escorts, as they lacked training, doctrine, and sufficient anti-aircraft guns. These deficiencies would eventually doom Kaga and other First Air Fleet carriers.[47]

In May 1999, the Nauticos Corporation, in partnership with the US Navy, discovered some wreckage from Kaga.[72] They employed the research vessel Melville during a survey of a fleet exercise area with the US Navy's recently modified SEAMAP acoustic imaging system. A follow-on search by USNS Sumner in September 1999 located the wreckage and took photos of it.[73] The wreckage included a 50-foot (15 m) long section of hangar bulkhead, two 25 mm anti-aircraft gun tubs, and a landing light array. The artifacts were at a depth of 17,000 feet (5,200 m).[74]

On 18 October 2019, the wreck of Kaga was located by the Director of Undersea Operations for Vulcan Inc. Rob Kraft and Naval History and Heritage Command historian Frank Thompson aboard RV Petrel. She sits upright at a depth of about 18,000 ft (5.4 km), buried up to the degaussing wires in the seafloor and with most of her superstructure and flight deck missing. The wreck is surrounded by a large debris field and has been heavily colonized by marine growth.[75] The wreck of Akagi was found by the same crew two days later.[76]

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