Japanese aircraft carrier Hōshō

Hōshō (鳳翔) was the world's first commissioned ship that was designed and built as an aircraft carrier, and the first aircraft carrier of the Imperial Japanese Navy (IJN). Commissioned in 1922, the ship was used for testing carrier aircraft operations equipment, techniques, such as take-offs and landings, and carrier aircraft operational methods and tactics. The ship provided valuable lessons and experience for the IJN in early carrier air operations. Hōshō superstructure and other obstructions to the flight deck were removed in 1924 on the advice of experienced aircrews.

Hōshō and her aircraft group participated in the Shanghai Incident in 1932 and in the opening stages of the Sino-Japanese War in late 1937. During those two conflicts, the carrier's aircraft supported Imperial Japanese Army ground operations and engaged in aerial combat with aircraft of the Nationalist Chinese Air Force. The small size of the ship and her assigned airgroups (usually around 15 aircraft) limited the effectiveness of her contributions to combat operations. As a result, the carrier was placed in reserve after her return to Japan from China and she became a training carrier in 1939.

During World War II, Hōshō participated in the Battle of Midway in June 1942 in a secondary role. After the battle, the carrier resumed her training role in Japanese home waters for the duration of the conflict and survived the war with only minor damage from air attacks. She was used as a repatriation transport after the war, making nine trips to bring some 40,000 Japanese soldiers and civilians to Japan from overseas locations. Hōshō was scrapped in Japan beginning in 1946.

Design and description
Construction of a seaplane carrier was authorized by the Japanese government in its "eight-six" fleet program of 1918. A planned sister ship, named Shokaku, was cancelled in 1922 before any construction started. Hōshō was the second warship, after the British HMS Hermes (95), to be designed from the keel up as an aircraft carrier, but was launched and completed earlier than Hermes.

Hōshō was planned as a seaplane carrier like the British HMS Campania (1914) with a forward flying-off deck, 32 aircraft, four low-angle 14 cm guns, and four anti-aircraft (AA) guns. The plan was revised after reports were received from Japanese observers with the Royal Navy in Europe about the desirability to be able to land aircraft on the ship. The new requirements were modeled on HMS Furious (47) after she received her rear flight deck in 1918. The ship was to be capable of 30 kn and fitted with a forward flight deck, superstructure and funnels amidships, and a large hangar aft. Shortly thereafter based on observations of landing trials on Furious and HMS Argus (I49), the world's first flush-decked aircraft carrier, Hōshō's flight deck design was revised in April 1919. The superstructure was removed and the funnels were moved to one side to create an unobstructed, full-length flight deck, and the ship was reclassified as an aircraft carrier. The ship's hull was based on that of a large cruiser and she was given a small island. Her three funnels were mounted on the starboard side and swiveled to lie horizontal during flight operations. Hōshō's designed speed was reduced to 25 kn, based on British experiences during World War I.

General characteristics


Hōshō was completed with an overall length of 168.25 m. She had a beam of 17.98 m and a mean draft of 6.17 m. The ship displaced 7470 LT at standard load, and 9494 LT at normal load. Her crew totaled 512 officers and men. The ship was almost completely unarmored.

Propulsion
Hōshō had two Parsons geared turbine sets with a total of 30000 shp driving two propeller shafts. Eight Kampon Type B water-tube boilers with a working pressure of 18.3 kg/cm2 and a temperature of 138 °C provided steam to the turbines, although only four were oil-fired. The other four used a mix of oil and coal. The ship's designed speed was 25 knots, but she made 26.66 kn from 31117 shp on her sea trials on 30 November 1922. She carried 2700 LT of fuel oil and 940 LT of coal, an extraordinary total for such a small ship, to give her a range of 8680 nmi at 12 kn.

To reduce rolling and increase stability for aircraft operations, a gyrostabilizer produced by the American Sperry Gyroscope Company was installed. The installation initially proved unreliable as the Japanese technicians were badly trained by Sperry, but eventually the system proved its worth as the technicians gained experience.

Flight deck arrangements
Hōshō's flight deck was 168.25 m long and 22.62 m wide. The forward end sloped down at an angle of −5° to help aircraft accelerate during takeoff. A small island was mounted well forward on the starboard side and contained the ship's bridge and air operations control center. The island was fitted with a small tripod mast intended to mount the ship's fire-control system. Fifteen different types of landing equipment were evaluated before the British longitudinal wire system was adopted. Low landing speeds of the time meant that aircraft had little difficulty in stopping, but their light weight made them vulnerable to wind gusts that could blow them over the side of the carrier, and the longitudinal wires helped to prevent that. Forward of the island was a collapsible crane for loading aircraft into the forward hangar.

The flight deck, unlike those on Royal Navy carriers, was superimposed on the ship's hull rather than constructed as a strength deck supporting the carrier's hull structure. A system of lights and mirrors along the flight deck assisted pilots in landing on the carrier.

Hōshō was the only Japanese aircraft carrier with two hangars. The forward hangar was 67.2 by and only one deck in height as it was intended to house nine small aircraft, such as fighters. The two-story rear hangar measured 16.5 by at the forward end and 29.4 by at the rear end. It was designed to house six large aircraft, such as torpedo bombers, as well as six reserve aircraft. Each hangar was served by an aircraft elevator. The forward elevator was 10.35 by and the aft elevator measured 13.71 by.

Air group
Hōshō had a normal capacity of fifteen aircraft, subject to the limitations of her hangars. She was first commissioned with an air group of nine Mitsubishi 1MF (Type 10) fighters and three to six Mitsubishi B1M3 (Type 13) torpedo bombers. In 1928 the fighters were replaced by the A1N1 (Type 3). Three years later the air group consisted of Nakajima A2N (Type 90) fighters and Mitsubishi B2M (Type 89) torpedo bombers. In 1938 Nakajima A4N (Type 95) fighters and Yokosuka B3Y (Type 92) bombers flew from the ship. In 1940 the air group was modernized with Mitsubishi A5M (Type 96) "Claude" fighters and Yokosuka B4Y1 (Type 96) "Jean" bombers.

Armament
Hōshō was armed with four 50-caliber 14 cm/50 3rd Year Type guns, two on each side. The two forward guns had a firing arc of 150°, including straight ahead, while the rear guns could fire 120° on either side. They fired 38 kg projectiles at a rate of six to ten rounds per minute with a muzzle velocity of about 850 m/s; at 35°, they had a maximum range of 19750 m. A heavy gun armament was provided for Hōshō; as carrier doctrine was just evolving at this time, the impracticability of carriers engaging in gun duels had not yet been realized. Her large flight deck and lack of armor made her a vulnerable target in surface battles.

A pair of 40-caliber 8 cm/40 3rd Year Type guns on disappearing mounts provided Hōshō's only anti-aircraft defense. They were positioned on the flight deck, just forward of the rear elevator. These guns fired 5.67 - 5.99 kg projectiles at a muzzle velocity of about 680 m/s; at 45° this provided a maximum range of 10800 m, and they had a maximum ceiling of 7200 m at 75° elevation. Their effective rate of fire was 13 to 20 rounds per minute.

Early career
Hōshō's keel was laid down by the Asano Shipbuilding Company in Tsurumi-ku, Yokohama, on 16 December 1920. She was launched on 13 November 1921 and towed to Yokosuka Naval Arsenal for completion on 10 January 1922. Hōshō was delayed by repeated design changes and late deliveries of equipment, pushing the commissioning date from March to 27 December 1922. She was commissioned lacking much of her aviation equipment, and did not begin landing trials until 22 February 1923. The first landings were made by British pilots under contract, who were quickly replaced by Japanese pilots trained by the British Aviation Mission.

After Hōshō was commissioned, experienced aircrews requested changes, and the ship was modified by the Yokosuka Navy Arsenal from 6 June to 20 August 1924. The island, tripod mast, and aircraft crane were removed since they partially obstructed the flight deck and obscured pilot visibility. The forward part of the flight deck was made horizontal, and the 8 cm AA guns were moved forward, close to the position of the former island and out of the way of landing operations. After the island was removed, the carrier's flight operations were controlled from a platform extending from the side of the flight deck, a design that would be repeated in subsequent Japanese aircraft carriers. The ship was then assigned to the 1st Fleet until 15 November 1924.

Hōshō was fitted with a net used as a crash barrier aft of the forward elevator between 10 March and 2 July 1925. The barrier was intended to prevent landing aircraft from colliding with aircraft preparing to take off, and stop them from falling into the open elevator well. The barrier was hydraulically operated and could be erected in three seconds.

As the first of her kind, Hōshō provided valuable experience and insight into carrier air operations for the IJN. The ship was used for testing aircraft and equipment, particularly various types of arresting gear and optical landing aids. The lessons learned influenced the design and construction of JAPANESE AIRCRAFT CARRIER Ryūjō and the subsequent conversions of JAPANESE AIRCRAFT CARRIER Akagi and JAPANESE AIRCRAFT CARRIER Kaga into aircraft carriers. Hōshō was actively used to develop carrier operational methods and tactics for the IJN during the 1920s. She was assigned to the First Carrier Division with Akagi on 1 April 1928. During the 1930s Hōshō was fitted with three different types of transverse arresting gear for trials.

Shanghai
Along with Kaga, Hōshō was assigned to the First Carrier Division and sent to China during the Shanghai Incident that began in January 1932. Operating with the Third Fleet, Hōshō arrived at the mouth of the Yangtze River on 1 February. Her aircraft participated in the IJN's first aerial combat on 5 February when three fighters, escorting two attack aircraft, were engaged by nine Chinese fighters; one Chinese fighter was damaged. Two days later the two carriers sent some of their aircraft to Kunda Airfield where they flew ground attack missions in support of the Imperial Japanese Army. Between 23 and 26 February, Kaga and Hōshō bombers attacked Chinese airfields at Hangzhou and Suzhou, destroying a number of Chinese aircraft on the ground. On 26 February six fighters from Hōshō, escorting nine attack aircraft from Kaga on one of the bombing raids, shot down two of five Chinese fighters that engaged them. The First Carrier Division rejoined the Combined Fleet on 20 March, after a ceasefire had been declared on 3 March.

Fourth Fleet Incident
Hōshō participated in the Combined Fleet Maneuvers of 1935 where she was attached to the IJN Fourth Fleet. The fleet was caught out in a typhoon on 23 September. The carrier and a number of other Japanese ships were badly damaged in what was referred to as the "Fourth Fleet Incident." The ship's forward flight deck collapsed and part had to be cut away before the carrier could proceed to Yokosuka for repairs. The Fourth Fleet Incident and the Tomozuru Incident of 1934, in which a top-heavy torpedo boat capsized in heavy weather, caused the Japanese command to investigate the stability of all their ships, resulting in a number of design changes to improve stability and increase hull strength.

While the Hōshō was at the dockyard between 22 November 1935 and 31 March 1936, her stability was improved; the forward flight deck's supports were reinforced and increased in number; the ship's AA guns, aircraft crane and upper deck aviation fuel tanks were removed; the funnels were fixed in the horizontal position with their mouths angled slightly downwards; the front sides of Hōshō's forward hangar and bridge were reinforced; and the ship's hull was reinforced in the vicinity of her rear hangar to increase her longitudinal strength. At full load, her metacentric height after these changes was 1.11 m. Six twin 13.2 mm Type 93 Hotchkiss machine guns were also fitted.

Sino-Japanese War
During the Sino-Japanese War, Hōshō returned to the Third Fleet and supported land operations of the army in China around August or October 1937 with Ryūjō, later joined by Kaga. Hōshō's air unit began flying ground support missions in the Shanghai area on 16 July. Three of the ship's Nakajima A2N fighters engaged two Martin B-10 heavy bombers on 25 July, shooting down one of them.

The ship departed on 1 September to refuel, but did not return to the Shanghai area. Accompanied by Ryūjō she sailed to the South China coast and began operations against Chinese forces near Canton on 21 September. On that day Hōshō contributed six fighters to escort bombers attacking airfields at Tienho and Paiyun. They claimed six enemy aircraft shot down, but the range proved to be too long. Five of the fighters ran out of fuel and had to ditch in the sea, although the aircrews were rescued. Hōshō and Ryūjō bombers continued with almost daily attack missions until the end of September. Hōshō and Ryūjō returned to the Shanghai area on 3 October and Hōshō's aircraft were temporarily transferred to Kunda airfield to support ground operations. On 17 October, Hōshō transferred all of her aircraft to Ryūjō and returned to Japan.

Hōshō was placed in reserve on 1 December 1937. Her aircraft elevators were enlarged in 1939: the forward elevator to 12.8 by and the rear elevator to 13.7 by. On 12 August 1939 Hōshō was deemed useful as a training carrier and, in critical battles, as a platform for A4N1 (Type 95) fighters and B4Y1 (Type 96) torpedo bombers, for as long as those planes remained serviceable. A later investigation determined on 23 December 1940 that she could not operate the latest aircraft types like the Mitsubishi A6M Zero, the Aichi D3A "Val", or the Nakajima B5N "Kate" in combat. Also, the small size of the carrier's airgroup limited the ship's potential value to the fleet in any future conflicts.

Pearl Harbor and Midway
Hōshō began the Pacific War in the Third Carrier Division assigned to the 1st Fleet under Vice Admiral Shirō Takasu. The carrier, captained by Karou Umetani, was tasked along with Zuihō to provide air support, including scouting, anti-submarine patrols, and combat air patrol for the Combined Fleet's "Main Body" battle-line of six battleships: Nagato, Mutsu, Fusō, Yamashiro, Ise, and Hyūga. With the Main Body, Hōshō sortied from the Inland Sea on 7 December 1941 to provide distant cover for the carrier forces under Chūichi Nagumo which were attacking Pearl Harbor. The battleship force turned back 300 nmi east of Japan, but Hōshō became separated on 10 December due to radio silence restrictions while conducting anti-submarine air operations. The carrier was located by scout aircraft the next day 500 nmi east of the Main Body and returned to port at Kure on 12 December.

On 29 May 1942 Hōshō sortied from Japan with the rest of the fleet for the operation which resulted in the Battle of Midway, providing modest air protection, scouting, and anti-submarine support for the Main Body, now consisting of the battleships Yamato, Nagato, and Mutsu. Her aircraft complement for the operation consisted of eight obsolete Yokosuka B4Y carrier attack aircraft (torpedo bombers).

With the Main Body trailing 300 nmi behind the carrier striking force, Hōshō missed the major portion of the battle in which Nagumo's four fleet carriers were ambushed and fatally damaged by US carrier aircraft on 4 June. The next day, Hōshō aircraft helped guide the remnants of Nagumo's force to a rendezvous with the Main Body. Around the same time, one of Hōshō's aircraft, crewed by pilot Shigeo Nakamura and observer Kiyoshi Ōniwa, discovered the burning, sinking JAPANESE AIRCRAFT CARRIER Hiryū. Photographs of the abandoned carrier taken by Ōniwa have been described as "among the most dramatic of the war in the Pacific." With the battle lost, a significant strategic defeat for Japan, the carrier returned to Japan with the rest of the fleet, arriving at the Hashirajima anchorage on 14 June.

Training ship
After her return to Japan Hōshō was transferred to the Third Fleet, unofficially assigned to the training fleet (later called the Mobile Force Training Force), and officially assigned in October. She conducted flight training in the Inland Sea for aircraft that flew in from shore bases, since no aircraft were based on board Hōshō. On 15 January 1943, the 50th Air Flotilla was created for carrier aircrew training and both Hōshō and Ryūhō were assigned to the new unit. The two ships provided carrier landing training and served as target ships for torpedo training. In January 1944, Hōshō was reassigned to the 12th Air Fleet, then to the Combined Fleet, but continued to perform the same mission of training fleet carrier pilots in the Inland Sea. In this role, Hōshō shuttled back and forth between Kure and the Western Inland Sea, spending equal amounts of time at each location.

In order to service new and larger aircraft like the Nakajima B6N "Jill" torpedo bomber and the Yokosuka D4Y "Judy" dive bomber, the flight deck was extended over 6 m at each end to a total length of 180.8 m from 27 March to 26 April 1944. Hōshō also received new arresting gear and a new crash barrier. The additional weight high up in the ship adversely affected her stability and she was restricted from operations in bad weather lest she capsize. At some point during the war the ship's 14 cm guns were removed and she received about twenty 25-millimeter Type 96 autocannons in single mounts. They fired .25 kg projectiles at a muzzle velocity of 900 m/s; at 50°, this provided a maximum range of 7500 m, and an effective ceiling of 5500 m. The 15-round magazines needed to be changed frequently, and the maximum effective rate of fire was only between 110 and 120 rounds per minute.

After the modifications, Hōshō continued to provide training to navy pilots in the Inland Sea, including acting as a target ship for torpedo training. At 05:30 on 19 March 1945, possibly while berthed at Kure, the carrier was caught in an air raid by carrier aircraft from the United States Task Force 58. Hōshō's flight deck was damaged by three bomb hits which killed six crewmen. Emergency repairs were made and her captain was ordered to keep her in readiness on 10 April. However, this order was revoked two days later and the carrier became a "4th reserve ship" with most of her crew transferred elsewhere. Hōshō was taken out of reserve as a "special guard ship" on 1 June and many of her crew were transferred back. During this time, the ship remained moored and camouflaged off Nishinomishima at Kure.

Hōshō was slightly damaged by a single bomb or aerial rocket hit when the Allies attacked Kure again in July 1945. Information is scarce on the extent of the ship's involvement in the action, but it appears the carrier's participation was minimal, as it embarked no aircraft at the time. Hōshō was repaired within 15 days, but the termination of hostilities in September 1945 found the carrier still docked at Kure.

Post-war
After the war, Hōshō served as a repatriation transport to retrieve Japanese servicemen and civilians stationed overseas and return them to Japan. In October and November 1945, accompanied by the cruiser Kashima, she carried 700 passengers from Wotje Atoll, 311 from Jaluit Atoll, and an undocumented number from Enewetak Atoll to Uraga, Kanagawa.

In December 1945, Hōshō's overhanging flight deck at the bow was cut off and her hangars were modified to carry more passengers. Thereafter, she undertook more repatriation missions beginning with one to Wewak on 5 January 1946 and subsequent trips to China. In total, the carrier made nine repatriation trips before 15 August 1946 and transported about 40,000 passengers.

Hōshō was transferred to the Ministry of the Interior on 31 August for disposal. She was scrapped in Osaka from 2 September 1946 to 1 May 1947 by the Kyôwa Shipbuilding Company.