The Shokakus were in many respects the most successful Japanese carriers of the Second World War. This is the name-ship, shortly after commissioning. Note the enclosed gun mountings abaft the funnels, affording a measure of habitability to the crews.
These two carriers were a substantial enlargement of the successful Hiryu design with greater protection, a more powerful antiaircraft battery, and an expanded air group. They were equipped with two catapults forward, the first aboard Japanese carriers.
The two fleet carriers designed in 1936-37 were without question the most successful operated by the Imperial Japanese Navy; they had all the virtues and few of the vices of the Soryus and were, moreover, considerably larger, better armed and more heavily armoured, and could accommodate a larger air group. Their one principal defect was the light construction of the flight deck, aggravated by totally enclosed yet unprotected double hangars and unsatisfactory petrol bunkerage, but of course the proof of this was not available at the time of their conception.
The Imperial Japanese Navy’s practice for landing operations was for aircraft to orbit to one side of the carrier, peeling off and landing as ordered by the air operations officer. When a koku-sentai operated in formation, the carriers were abreast one another, each carrier’s aircraft were orbiting outboard of the formation, and it was considered advantageous to locate the islands to suit. In practice, this island location proved to have serious disadvantages: it limited the landing space, caused excess air turbulence over the flight deck, and obstructed the normal path for aborted landings. Consequently, by the time the carriers of the Shokaku class were fitting out for service, this island arrangement was abandoned in favor of the conventional position forward of amidships on the starboard side.
A longer, beamier hull allowed the provision of heavy-cruiser type 6.5in belt armour along the magazines, reinforced with a further 1.8in across the machinery spaces, with a 3-9in armour deck over the latter and 5.1 in over the former. The bulged clipper bow which would also be a feature of the Yamato class battleships was also incorporated, while extremely powerful machinery bestowed a high sustained sea speed. The original design reportedly envisaged islands to port on one ship and to starboard on the other, together with a funnel to port and to starboard on each, but the ships as completed were generally similar, with both superstructure and uptakes on the starboard side.
The Shokaku and the Zuikaku were unique among Japanese carriers in carrying a pair of catapults, derived from units developed for use on the Yamato-class battleships, on the flight deck.
The wooden flight deck, planked except in the region of the two converging catapult tracks forward and over the boiler uptakes, was serviced by three lifts measuring 42ft 6in x 52ft 6in (forward), 42ft 6in x 39ft 4in (amidships) and 38ft 6in x 42ft 6in (aft), and there were eight transverse arrester wires aft and three further forward, with a hinged screen abaft the catapults to provide a wind break. Eight twin 5in / 40 were disposed along the deck edge in pairs forward and aft, and the 25mm triple mountings were distributed along the flight-deck edge, those abaft the funnel on the starboard side being enclosed as in most other Japanese carriers.
The original designed air group numbered 96 machines (24 B5N torpedo-bombers, 24 D1A dive-bombers, twelve A5M fighters, twelve C3N reconnaissance planes, 24 reserves), but with the cancellation of the C3N and the phasing out of the D1A and A5M the air group upon completion consisted of 27 B5N, 27 D3A (`Val’) dive-bombers and eighteen A6M fighters, with twelve machines in reserve. Trial displacement for each carrier was 29,330 tons.
Japanese carrier development during World War II in large part continued the two central themes of prewar design efforts: a search for both qualitative excellence in individual vessels and for quantitative equality or superiority relative to the United States Navy. The search for qualitative excellence was demonstrated by the Taiho, which combined the performance and aircraft capacity of the Shokaku class (the epitome of Japanese prewar design) with greatly enhanced protection, while the demand for quantity production was exemplified by the Unryu class and the Imperial Japanese Navy’s very extensive “shadow” carrier fleet. The limitations of Japan’s industrial base made this an impossible task. Most of the “shadow” carrier designs required major qualitative concessions of speed, aircraft capacity, or protection that limited their contribution to carrier task force capabilities, the Unryu class represented a step back in Japanese carrier quality, and the Imperial Japanese Navy abandoned its hopes of producing further carriers of the Taiho’s excellence.
As was the pattern in the US and Royal Navies, wartime modifications to the surviving units of Japan’s carrier fleet were concerned principally with the upgrading of the anti-aircraft battery. By the summer of 1942 both Shokaku and Zuikaku had had two additional triple 25mm mountings added at the stern and two at the bows, bolstered later that year with a third at both bow and stern and sixteen single 25mms forward. By the time of her loss Zuikaku had received even more weapons – two more triples, one before and one abaft the island, and twenty more singles, half of which were portable and, operating independently of the ship’s power supply, were dispersed about the flight deck during periods when aircraft were not operating; there were also six 28-barrelled rocket-launchers forward. At some time during 1943-44 both carriers received Type 13 air warning and Type 21 air/surface warning radar systems [Some writers refer to the Type 13 as `Type 3 Mk T and to the Type 21 as `Type 2 Mk 2′.], and following her near-loss in May 1944 Zuikaku had her petrol bunkers reinforced with concrete in an effort to exclude air from the spaces surrounding them and hence mixing with the vapour.
Shokaku: It seems likely that the timing of the Japanese attack on Pearl Harbor, 7 December 1941, was determined partly by the fact that both Shokaku and Zuikaku would by then be ready for combat, and both carriers played a leading role in that venture. Shokaku carried out raids on New Guinea the following month, and in May 1942 was seriously damaged in the Coral Sea when hit by three bombs; her aircraft accounted for Lexington during that action, but on her return to Japan for repairs she almost sank. She was hit once during the Battle of Eastern Solomons (August 1942), and very badly damaged during her next major engagement, Santa Cruz (October 1942), when she was caught by aircraft from Hornet and received six direct bomb hits. On 19 June 1944, in the Battle of the Philippine Sea, she was sunk by four torpedoes fired by the submarine Cavalla afire and badly listing, she eventually turned turtle.
Zuikaku’s career followed that of her sister-ship for the first six months of the war, her aircraft also being involved in the sinking of Lexington. She escaped damage in that action, and subsequently took part in the Aleutians operations. Zuikaku was seriously mauled during the Battle of the Philippine Sea, but her crew managed to overcome the fires which threatened to engulf the carrier. In October 1944, however, while assisting in feints to draw the US carriers supporting the Leyte Gulf landings (Cape Engano), she was hit first by one torpedo and later by a further six torpedoes and seven bombs and was sunk (25th).