Hiryū (飛龍, meaning "Flying Dragon") was a modified Sōryū-class aircraft carrier of the Imperial Japanese Navy. She was one of the carriers that began the Pacific War with the attack on Pearl Harbor. After being heavily damaged by air attacks 4 June 1942 at the Battle of Midway, Hiryu sank on 5 June 1942.
The ship was built within the specifications of the Washington Naval Treaty that was in place at the time, which placed limits on its tonnage and armament. As a result, the Sōryū and Hiryū were relatively small as fleet aircraft carriers compared to their contemporaries during World War II, carrying around 70 aircraft. Compared to her near sister Sōryū, Hiryū was almost four feet greater of beam, 2,000 tons heavier, and had her island superstructure placed on the port side and farther aft on her flight deck. 
The Hiryū was also built with the deficiencies of the Ryujo in mind , which suffered from topweight problems as well as a small flight deck that delayed flight operations. Compared to the Ryujo, the Hiryu had a larger flight deck, hull and an endurance distance extended by nearly 3000 miles.
The port side island was an unusual arrangement; the only other carrier to share this feature was the Japanese aircraft carrier Akagi. The Akagi and the Hiryū were intended to work in a tactical formation with starboard-sided carriers, in order to improve the flight pattern around the formation, but the experiment was not continued beyond those two carriers.  The enlarged bridge design created turbulence, causing far greater deck accidents in the Hiryū than her sister carrier.
In 1941, commanded by Captain Tomeo Kaku, Hiryū was assigned to Carrier Division 2. On 7 December 1941 she was with the Strike Force in the attack on Pearl Harbor. She launched one wave of planes against the island of Oahu: ten Kates targeted Arizona, California, eight Kates targeted West Virginia, Oklahoma, and Helena and six Zeros attacked US air bases at Wheeler Field and Barbers Point.
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