Silverstone, p. 330 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.Milanovich, pp. 10–11; Evans and Peattie, p. 180 A planned sister ship, named Shokaku, was cancelled in 1922 before any construction started.Watts, p. 169 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.Evans and Peattie, pp. 181–182

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.Milanovich, pp. 9, 11

General characteristics

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.Milanovich, pp. 22–23 The ship was almost completely unarmored.Evans and Peattie, p. 323

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 .Milanovich, p. 15

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

Hōshōs flight deck was long and 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 carry the ship's fire-control system. Fifteen different types of arresting gear 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.Milanovich, p. 13Evans and Peattie, p. 315

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 and only one deck in height as it was intended to house nine small aircraft, such as fighters. The two-story rear hangar measured at the forward end and 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 and the aft elevator measured .Milanovich, pp. 13, 15, 22

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.Hata, Izawa and Shores, p. 2

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.Milanovich, p. 14 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 .Campbell, p. 190 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.Peattie, pp. 53, 55

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.Campbell, p. 198

Service

Early career

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. The first landings were made by British pilots under contract, who were quickly replaced by Japanese pilots trained by the British Aviation Mission.Milanovich, pp. 11, 15–16 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.Milanovich, pp. 17, 21 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. 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.Peattie, p. 53 The ship was then assigned to the 1st Fleet until 15 November 1924.

Hōshō was fitted with a net used as a barricade aft of the forward elevator between 10 March and 2 July 1925. It 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.Milanovich, pp. 17, 21; Peattie, p. 53

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.Milanovich, pp. 20–21Watts, p. 169; Evans and Peattie, p. 315; Parshall and Tully, p. 7; Peattie, p. 229

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 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.Hata, Izawa and Shores, pp. 2–3Peattie, pp. 50–51

Fourth Fleet incident