was the world's first commissioned ship that was 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 ship 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 surrendered to the Allies at the end of the war and used to repatriate Japanese troops until she was scrapped 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 , to be built from the keel up as an aircraft carrier, but was launched and completed earlier than Hermes.
Hōshō was initially designed as a seaplane carrier like with a forward flying-off deck, 32 aircraft, four low-angle 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 after she received her rear flight deck in 1918. The ship was to be capable of and fitted with a forward flight deck, island and funnels amidships, and a large hangar aft. Shortly thereafter based on observations of landing trials on Furious and , the world's first flush-decked aircraft carrier, Hōshōs flight deck design was revised in April 1919. The island 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. Hōshōs designed speed was reduced to , based on British experiences during World War I.
General characteristics
thumb|left|Hōshō conducts full-power trials with funnels swiveled up near [[Tateyama, Japan, on 4 December 1922]]
Hōshō was completed with an overall length of . She had a beam of and a mean draft of . The ship displaced at standard load, and 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 driving two propeller shafts. Eight Kampon Type B water-tube boilers with a working pressure of and a temperature of 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 from on her sea trials on 30 November 1922. She carried of fuel oil and of coal, an extraordinary total for such a small ship, to give her a range of at .
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.
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.
Air group
thumb|right|Hōshō (middle) compared with other aircraft carriers constructed during the same time period
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. They fired projectiles at a rate of six to ten rounds per minute with a muzzle velocity of about ; at 35°, they had a maximum range of . 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 retractable mounts provided Hōshōs only anti-aircraft defense. They were positioned on the flight deck, just forward of the rear elevator. These guns fired projectiles at a muzzle velocity of about ; at 45°, this provided a maximum range of , and they had a maximum ceiling of at 75° elevation. Their effective rate of fire was 13 to 20 rounds per minute.
Service
Early career
thumb|Hōshō in 1924 after her [[Glossary of nautical terms (A-L)#island|island was removed]]
Hōshō 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.
After Hōshō was commissioned, experienced aircrews requested changes, and the ship was modified by the shipyard 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. Another reason for removal of the island was that the IJN found that it was too small and cramped to be of effective use in controlling air operations or conning the ship. The ship was then assigned to the 1st Fleet until 15 November 1924.
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 and the subsequent conversions of battlecruiser and battleship 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
thumb|right|Hōshō conducts air operations around the time of the Shanghai Incident
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 over Shanghai; one Chinese fighter was damaged, although the Japanese pilots made no claim. 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 three 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 during which she was attached to the IJN Fourth Fleet. Caught 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 Hōshōs 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 . Six twin 13.2 mm Type 93 Hotchkiss machine guns were also fitted.
The carrier returned to Japan to refuel on 1 September and then sailed to the South China coast, accompanied by Ryūjō, and began operations against Chinese forces near Canton, now Guangzhou, on 21 September. That day, Hōshō contributed six fighters to escort bombers attacking airfields and the combined force encountered seven Curtiss Hawk III fighters, shooting down two, in addition to a pair of observation planes, for no combat losses of their own. Five of the Japanese fighters ran out of fuel during the return flight and had to ditch in the sea, although the aircrews were rescued. A followup air strike that afternoon was unsuccessfully attacked by the five remaining Hawks, at the cost of one of their own. The Japanese pilots claimed to have shot down sixteen enemy aircraft and an additional probable loss during the day's fighting. Hōshō and Ryūjō returned to the Shanghai area on 3 October and Hōshōs aircraft were temporarily transferred to Kunda airfield to support ground operations. On 17 October, the carrier transferred all of her aircraft to Ryūjō and returned to Japan where she was placed in reserve on 1 December.
During this time, her aircraft elevators were enlarged in 1939: the forward elevator to and the rear elevator to . 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.
World War II
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 Kaoru Umetani, was tasked along with 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: , , , , , and . 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 east of Japan, but Hōshō became separated on 10 December due to radio silence restrictions while conducting anti-submarine air operations. The ship lost contact because she had launched aircraft near dusk to investigate a submarine sighting. The aircraft returned after dark and landed safely after the carrier turned on its lights. In order to recover the aircraft, however, the carrier and her three escorting destroyers had to steam east and therefore lost sight of the Main Body in the darkness. There does not appear to have been any enemy submarines in Japanese waters at this time. The carrier was located by scout aircraft the next day east of the Main Body and returned to port at Kure on 12 December.
thumb|Hiryū on 5 June 1942 during the Battle of Midway, photographed from a [[Yokosuka B4Y biplane launched from Hōshō]]
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 , Nagato, and Mutsu. Her aircraft complement for the operation consisted of eight obsolete Yokosuka B4Y "Jean" torpedo bombers.
With the Main Body trailing 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, the carrier's aircraft helped guide the remnants of Nagumo's force to a rendezvous with the Main Body as well helped other Japanese warships to rendezvous during and after the battle, including the cruiser . Around the same time, one of Hōshōs aircraft discovered the burning, sinking . Photographs of the abandoned carrier have been described as "among the most dramatic of the war in the Pacific". The observer aboard the aircraft also reported seeing survivors left behind on Hiryū so the destroyer was sent to unsuccessfully search for the wrecked carrier. 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 onboard 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. They fired projectiles at a muzzle velocity of ; at 50°, this provided a maximum range of , and an effective ceiling of . 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. Hōshōs 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 on 24 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 she embarked no aircraft at the time. Hōshō was repaired within 15 days, Hōshō was transferred to the Home Ministry on 31 August for disposal. She was scrapped in Osaka from 2 September 1946 to 1 May 1947 by the Kyōwa Shipbuilding Company.