Beyond her powerful battleships, the Empire of Japan owned a mighty carrier force by the time of World War 2 (1939-1945). This force proved instrumental in Japan's conquest of the Pacific and would feature equally important in neutralizing the American Navy in the inevitable showdown of titans. However, the Battle of Midway in 1942 saw the loss of four of these utterly important weapons to the Americans which forced Japan to compensate by, in the case of the Hiyo-class carrier group, in reworking existing passenger ocean liners to become dedicated fleet carriers. The group was led by IJN Hiyo (forged from SS Izumo Maru) and she was joined by her sister IJN Junyo (built atop the remains of SS Kashiwara Maru).
The conversion process, tackled by other navies of the period as well, made carrier acquisition both relatively economical and expedient.
In her original construction effort as SS Kashiwara Maru, the ship was ordered in late-1938 with construction assigned to the Nippon Yusen Kaisha shipyard (No. 900). The keel was laid down on March 20th, 1939 and the hull launched on June 26th, 1941. She was acquired, while still incomplete, by the Imperial Japanese Navy service on February 10th, 1941 and formally commissioned on May 3rd, 1942.
As completed, the warship had a displacement of 24,150 tons and dimensions that included a running length of 719.6 feet, a beam of 87.6 feet, and a draught down to 26.8 feet. Power was from 6 x Kampon water-tube boilers feeding 2 x Geared-steam turbines developing 56,250 horsepower driving 2 x Shafts astern. Maximum speed in ideal conditions reached 25.5 knots and range was out to 12,250 nautical miles. Armor protection reached up to 2" at the belt.
Aboard was a complement of up to 1,224 personnel. Internally she carried two hangar decks of limited size which meant her air arm was restricted to between forty-two and forty-eight total warplanes. Armament centered on self-defense measures led by 12 x 127mm Dual-Purpose (DP) guns in six twin-gunned mountings and 24 x 25mm Anti-Aircraft (AA) guns in eight triple-gunned emplacements.
For her time in World War 2, IJN Junyo became a veteran of the Aleutian Islands campaign (1942-1943), the Battle of Santa Cruz (1942), the Battle of the Philippine Sea (1944), New Guinea (1942-1945), and the Solomon Islands (1942-1945). In November of 1943, she took damage from Allied torpedoes which placed her out of action for the period of three months while repairs were enacted. In the Battle of the Philippine Sea, she was damaged once more, this time by aerial bombs from Allied warplanes and, in December of 1944, she was torpedoed again then laid up until March 1945. At this point, the effort to repair her and bring the vessel back into service was abandoned by Japanese authorities. The war then ended with the Japanese surrender in August 1945.
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