The consisted of two aircraft carriers built for the Imperial Japanese Navy (IJN) in the late 1930s. Completed shortly before the start of the Pacific War in 1941, the and were called "arguably the best aircraft carriers in the world" when built.Peattie, p. 243 With the exception of the Battle of Midway, they participated in every major naval action of the Pacific War, including the attack on Pearl Harbor, the Indian Ocean Raid, the Battle of the Coral Sea, the Guadalcanal Campaign, the Battle of the Philippine Sea and the Battle of Leyte Gulf (Zuikaku only).
Their inexperienced air groups were relegated to airfield attacks during the attack on Pearl Harbor, but they later sank two of the four fleet carriers lost by the United States Navy during the war in addition to one elderly British light carrier. The sister ships returned to Japan after the Battle of the Coral Sea, one to repair damage and the other to replace aircraft lost during the battle, so neither ship participated in the Battle of Midway in June 1942. After the catastrophic losses of four carriers during that battle, they formed the bulk of the IJN's carrier force for the rest of the war. As such they were the primary counterattack force deployed against the American invasion of Guadalcanal in the Battle of the Eastern Solomons in August. Two months later, they attempted to support a major offensive by the Imperial Japanese Army to push the United States Marines off Guadalcanal. This resulted in the Battle of the Santa Cruz Islands where they crippled one American carrier and damaged another in exchange for damage to Shōkaku and a light carrier. Neither attempt succeeded and the Japanese withdrew their remaining forces from Guadalcanal in early 1943 using the air group from Zuikaku to provide cover.
For the next year, the sisters trained before moving south to defend against any American attempt to retake the Mariana Islands or the Philippines. Shōkaku was sunk by an American submarine during the Battle of the Philippine Sea in June 1944 as the Americans invaded the Marianas and Zuikaku was sacrificed as a decoy four months later during the Battle off Cape Engaño.
Background and description
The two Shōkaku-class carriers were ordered in 1937 as part of the 3rd Naval Armaments Supplement Program. No longer restricted by the provisions of the Washington Naval Treaty, which had expired in December 1936, and with relaxed budgetary limitations, the IJN sought qualitative superiority over their foreign counterparts. Drawing on experience with their existing carriers, the Navy General Staff laid out an ambitious requirement for a ship that equaled the 96-aircraft capacity of the and , the speed of and and the defensive armament of Kaga. The new ship was also to have superior protection and range over any of the existing carriers.Lengerer, p. 90
The Basic Design Section of the Navy Technical Department decided upon an enlarged and improved Hiryū design with the island on the port side, amidships. After construction of the ships began, the Naval Air Technical Department (NATD) began having second thoughts about the location of the island because it thought that the portside location of the island on Hiryū and Akagi had an adverse impact on airflow over the flight deck. Another issue identified was that the amidships position shortened the available landing area, which had the potential to be problematic in the future as aircraft landing speeds increased with their growing weight. To verify these assumptions, the NATD filmed hundreds of takeoffs and landings aboard Akagi in October–November 1938 and decided to move the island over to the starboard side and further forward, about one-third of the length from the bow. Shōkaku was the furthest advanced by this point and the supporting structure for the bridge had already been built; rebuilding it would have delayed construction so it was left in place. The changes that had to be made consisted of a widening of the flight deck opposite the island and a corresponding narrowing on the starboard side and the addition of of ballast on the port side to re-balance the ship.Lengerer, pp. 91, 93
The ships had a length of overall, a beam of , a draft of at deep load, and a moulded depth of . They displaced at deep load. Based on hydrodynamic research conducted for the s, the Shōkaku class received a bulbous bow and twin rudders, both of which were positioned on the centerline abaft the propellers. Their crew consisted of 1,660 men: 75 commissioned officers, 56 special-duty officers, 71 warrant officers and 1,458 petty officers and crewmen, excluding the air group.Lengerer, pp. 93, 107
The Shōkaku-class ships were fitted with four Kampon geared steam turbine sets, each driving one propeller, using steam provided by eight Kampon Type Model B water-tube boilers. With a working pressure of , the boilers gave the turbines enough steam to generate a total of and a designed speed of . This was the most powerful propulsion system in IJN service, more than the Yamato class and the , respectively. During their sea trials, the sister ships achieved from . They carried of fuel oil which gave them a range of at . The boiler uptakes were trunked to the ships' starboard side amidships and exhausted just below flight deck level through two funnels that curved downward. The Shōkaku class was fitted with three turbo generators and two diesel generators, all operating at 225 volts.Lengerer, pp. 102–04, 106
Flight deck and hangars
The carriers' flight deck had a maximum width of 29 meters and overhung the superstructure at both ends, supported by pillars. Ten transverse arrestor wires were installed on the flight deck that could stop a aircraft. If the aircraft missed those, it could be stopped by one of three crash barricades. Although space and weight were allocated for two aircraft catapults, their development was not completed before the Shōkaku-class ships were sunk. The ships were designed with two superimposed hangars; the upper hangar was about long and had a width that varied between . It had a height of while the lower hangar was high and only usable by fighters. The lower hangar was about shorter than the upper one and its width ranged from . Together they had a total area of .Lengerer, pp. 93–95, 97–98 Each hangar could be subdivided by five or six fire curtains and they were fitted with fire fighting foam dispensers on each side. The lower hangar was also fitted with a carbon dioxide fire suppression system. Each subdivision was provided with a pair of enclosed and armored stations to control the fire curtains and fire fighting equipment.Dickson, pp. 18–19
Aircraft were transported between the hangars and the flight deck by three elevators that took 15 seconds to go from the lower hangar to the flight deck. The forward elevator was larger than the others to allow aircraft that had just landed to be moved below without folding their wings and measured . The other elevators were narrower, .Lengerer, p. 94 The ships mounted a crane on the starboard side of the flight deck, abreast the rear elevator. When collapsed, it was flush with the flight deck.Dickson, p. 17
The Shōkaku-class carriers were initially intended to have an air group of 96, including 24 aircraft in reserve. These were envisioned as 12 Mitsubishi A5M ("Claude") monoplane fighters, 24 Aichi D1A2 ("Susie") Type 96 dive bombers, 24 Mitsubishi B5M ("Mabel") Type 97 No. 2 torpedo bombers, and 12 Nakajima C3N Type 97 reconnaissance aircraft.Lengerer, p. 109 All of these aircraft were either superseded by larger, more modern aircraft or cancelled while the ships were being built, so the air group was revised to consist of 18 Mitsubishi A6M Zero fighters, 27 Aichi D3A ("Val") dive bombers, and 27 Nakajima B5N ("Kate") torpedo bombers.Chesneau, p. 171 In addition, the ship carried 2 Zeros, 5 "Vals", and 5 "Kates" as spares for a total of 84 aircraft.
Armament and sensors
The carriers' heavy anti-aircraft (AA) armament consisted of eight twin-gun mounts equipped with 40-caliber 12.7-centimeter (5 in) Type 89 dual-purpose guns mounted on projecting sponsons, grouped into pairs fore and aft on each side of the hull. The guns had a range of , and a ceiling of at an elevation of +90 degrees. Their maximum rate of fire was fourteen rounds a minute, but their sustained rate of fire was around eight rounds per minute.Campbell, pp. 192–93 The ship was equipped with four Type 94 fire-control directors to control the 12.7 cm guns, one for each pair of guns,Lengerer, p. 107 although the director on the island could control all of the Type 89 guns.Brown 1977, p. 23
Their light AA armament consisted of a dozen triple-gun mounts for license-built Hotchkiss 25 mm (1 in) Type 96 AA guns, six mounts on each side of the flight deck. The gun was the standard Japanese light AA weapon during World War II, but it suffered from severe design shortcomings that rendered it largely ineffective. According to historian Mark Stille, the weapon had many faults including an inability to "handle high-speed targets because it could not be trained or elevated fast enough by either hand or power, its sights were inadequate for high-speed targets, it possessed excessive vibration and muzzle blast".Stille 2007, p. 51 These guns had an effective range of , and a ceiling of at an elevation of +85 degrees. The effective rate of fire was only between 110 and 120 rounds per minute because of the frequent need to change the 15-round magazines.Campbell, p. 200 The Type 96 guns were controlled by six Type 95 directors, one for every pair of mounts.
In June 1942, Shōkaku and Zuikaku had their anti-aircraft armament augmented with six more triple 25 mm mounts, two each at the bow and stern, and one each fore and aft of the island. The bow and stern groups each received a Type 95 director. In October another triple 25 mm mount was added at the bow and stern and 10 single mounts were added before the Battle of the Philippine Sea in June 1944. After the battle, Zuikakus anti-aircraft armament was reinforced with 26 single mounts for the 25 mm Type 96 gun, bringing the total of 25 mm barrels to 96, 60 in 20 triple mounts and 36 single mounts. These guns were supplemented by eight 28-round AA rocket launchers.Lengerer, p. 105; Dickson, p. 25 Each rocket weighed and had a maximum velocity of . Their maximum range was .Campbell, p. 216
Shōkaku was the first carrier in the IJN to be fitted with radar, a Type 21 early-warning radar, mounted on the top of the island around September 1942. The date of Zuikakus installation is unknown, but both ships received a second Type 21 radar in a retractable installation adjacent to the flight deck after October. Before June 1944, a Type 13 air-search radar was installed on the light tripod mast abaft the island. The Shōkaku-class carriers were also fitted with a Type 91 hydrophone in the bow that was only useful when anchored or moving very slowly.Lengerer, pp. 101, 105; Dickson, pp. 27–28
Protection The Shōkaku class had a waterline belt that consisted of of Copper-alloy Non-Cemented armor (CNC) that covered most of the length of the ship. The belt was high, of which was below the waterline. The lower strake of the armor was backed by of Ducol steel. The magazines were protected by of New Vickers Non-Cemented (NVNC) armor, sloped at an inclination up to 25° and tapered to thicknesses of . The flight and both hangar decks were unprotected and the ships' propulsion machinery was protected by a deck of CNC armor. The NVNC armor over the magazines was thick and thick over the aviation gasoline storage tanks. All of the deck armor was overlaid on a 25-millimeter deck of Ducol steel.Lengerer, p. 100