USN Carrier Evolution XI: The Japanese carriers in WW II

Eleventh article in a series by Scot MacDonald. Reprinted with permission: Naval Aviation News, April 1963.

Japan is beaten, and carrier supremacy defeated her. Carrier supremacy destroyed her army and navy air forces. Carrier supremacy destroyed her fleet. Carrier supremacy gave us bases adjacent to her home islands … Carrier supremacy demolished the island air bases and eliminated the air force that was using them. Carrier supremacy made the island naval bases untenable for such shipping as escaped our submarines. Carrier supremacy permitted us to give close, tactical air support to the troops who stormed the island fortresses: VADM Marc A. Mitscher, USN, quoted in Naval Aviation News, October 1945.

HIJMS Shinano  was unknown to Allied intelligence until well after she was sunk by USS Archer-Fish (later Archerfish), in Japan’s home waters. Laid down as a Yamato class super-battleship, Shinano  was completed as an aircraft carrier following Japan’s disastrous losses in the Battle of Midway. Displacing 72,000 tons at full load, Shinano was the biggest carrier ever constructed until USS Forrestal  (80,000 tons, full load, commissioned 1955.) Shinano, launched 5 October 1944 and commissioned six weeks later, measured 266.1 x 36.3 x 10.8 metres (872.7 x 131 x 35.4 feet). Four screws and geared steam turbines fed by 12 boilers gave the ship 27 knots. Armament included 16 x 127 mm (five-inch), 145 x 25 mm guns and 330 x 130 mm rocket launchers. On her maiden voyage, from Yokosuka to Kure for outfitting, 28 November 1944, Archer-Fish scored four hits from six torpedoes fired at 0318. The carrier had sunk by 1100.
(No clear photographs of the carrier are known to exist. Sketch by LCDR Shizuo Fukui, 1950.)

When Japan struck Pearl Harbor on December 7, 1941, she had the strongest aircraft carrier force in the Pacific. This supremacy lasted until June 1942, when the Battle of Midway was fought and won by the USN. Thereafter, the bokubokan (mother ship for aircraft), though an effective and dangerous fighter, was an everweakening force; ships sunk by USN planes and submarines were not replaced in sufficient numbers and strength. The study of the Japanese maritime wartime construction is a study of desperation in the face of an inevitable defeat.

USS Archer-Fish SS-311, Shinano’s nemesis, was a Balao class submarine and measured 95 x 8.3 x 5.1 metres (311.75 x 27.25 x 16.8 feet) and displaced 1526/2391 tons surfaced/submerged. Her engines delivered a total of 5400/2740 shp surfaced/submerged, which gave her 20.5/8.75 knots respectively. Complement was 80 and armament included ten 533 mm (21 inch) torpedo tubes. Standing down from B-29 lifeguard duties off Tokyo on 28 November 1944, Archer-Fish spotted the carrier. Initially credited with sinking a heavy cruiser, this was changed to a 28,000-ton carrier. It was only after the war that the submarine was credited with sinking the largest warship ever destroyed by a single submarine.

At the outbreak of war, Japan had six fine bokubokan, the carriers Akagi,  Kaga,  Soryu, Hiryu, Shokaku and  Zuikaku , in addition to three lighter carriers, the  Zuiho, Hosho and  Ryujo . The keels were already laid for others and some conversions were being made. At that time, the USN had only seven carriers, widely dispersed. At the Battle of Midway, Japan lost  Kaga ,  Akagi ,  Hiryu and  Soryu , and never fully recovered from this decisive defeat.

First wartime construction

Japan’s first wartime-constructed carrier was the Taiho (Big Lucky Bird, aka Great Phoenix), authorised as a 29,300-ton ship under the 1939 estimates. Built at Kawasaki Dockyard, she was laid down in July 1941, launched in April 1943, and delivered in March 1944. She had a good cruising range of 10,000 miles at 18 knots, but could reach 33 knots with ease. Kawasaki claims that she was the most heavily protected flattop in the world at the time of her delivery. And well she might have been; her armour was impressive.

Taiho had 95 mm (3¾ inches) of plating on the flight deck between her two elevators, covering a distance of some 150 metres (492 feet). The platforms on these elevators were 51 mm (two inches) thick and weighed 100 tons. Such weight required a low centre of gravity for the ship, resulting in a very short distance between the waterline and the flight deck, the same height as that of the Hiryu, a carrier some 12,000 tons lighter.

HIJMS Taiho was another short-lived Japanese giant aircraft carrier that succumbed to an American submarine. Displacing 37,270 tons and capable of 33 knots from four shafts driven by 160,000 shp, her dimensions were 260.6 x 30 x 9.6 metres (855 x 98.5 x 31.5 feet). Commissioned 7 March 1944, Taiho was torpedoed by USS Albacore SS-218 in the early stages of the Battle of the Philippine Sea, 19 June 1944. A single torpedo jammed the forward elevator in a partly down position and fractured AVGAS lines. Some reports claim a quick repair scheme, constructing a wooden deck over the jammed lift, allowed restricted flight operations 30 minutes later. All reports agree that poor damage control led to massive internal AVGAS explosions about five hours afterwards that sent her to the bottom.

In designing and constructing this carrier, the slanting low smokestacks of her predecessors were abandoned and she returned to the “stack in island” type, the stack emerging high on the island and inclining outwards at 26 degrees.

Taiho was an excellent carrier, but she had a short life: three months. On  19 June 1944, during the Battle of the Philippine Sea, she was hit by a torpedo from the submarine Albacore, damaging gasoline pipes and jamming her forward elevator in the partly down position. Though her speed and manoeuvrability were not seriously affected, she did lose the ability to launch aircraft until the elevator well was shored up. AVGAS fumes spread through the ship. In a few hours she exploded and sank.

USS Albacore SS-218, a Gato class submarine, sank HIJMS Taiho, the flagship of a force steaming to interdict the Saipan landings. Ordered to move 100 miles south from his pre-briefed patrol position, Albacore‘s captain raised his periscope to find himself in the midst of a main carrier group, 19 June 1944. Allowing one carrier to pass, he selected Taiho  as a target but his Torpedo Data Computer malfunctioned. He fired all six bow tubes as the carrier was launching a strike. One Japanese pilot (Sakio Komatsu) saw the danger and deliberately dived onto one torpedo, exploding it, but another torpedo from the same spread found its mark. Albacore  was lost, 7 November 1944, after setting off a Japanese mine off the north-east coast of Hokaido.

Five modifications of the Taiho class were ordered in the 1942 program, but none was laid down, owing to shortages and crowded shipyards.

Unryu class

The Unryu (Cloudy Dragon) class was next to enter the scene. This ship was constructed under the 1941 estimates. Seven sister ships were ordered in the 1942 program. Two were never named and never laid down.

Unryu was a modification of the  Soryu , the plans simplified for quicker construction. She displaced 17,150 tons standard. Sister ships  Katsuragi and Aso were slightly heavier, displacing 17,400 tons, while  Ikoma ,  Kasagi and  Amagi were heavier yet, 18,300 tons. They had a speed of 34 knots, except for  Katsuragi and  Aso which, because of shortages, were equipped with destroyer-type engines and could only reach a relatively slow 32 knots.

Not one of these ships took an important part in any engagement. Both  Unryu and  Amagi were completed in August 1944 and were used for transport duty. Exactly 105 days after her commissioning, Unryu was sunk by a torpedo from the submarine  Redfish. Amagi suffered two attacks from USN carrier-based aircraft while the ship was at Kure. The second attack, on 24 July 24, 1945, capsized her. Katsuragi also came under attack by US carrier planes four days later, also at Kure. She suffered minor damage because she was protected by camouflage. After the war, she was used for repatriation and was scrapped in 1947.

Material shortages

Neither Aso, Kasagi nor Ikoma was completed by the end of the war. Aso was launched 1 November 1944,  Ikoma on 17 October, and  Kasagi two days later. They were 60 to 80 per cent complete when work on them was halted because of material shortages. Aso was used as a target ship for kamikaze training attacks and did not survive this abuse.  Ikoma was moored at Shodo Jima where she sustained bomb damage toward the end of the war. She and Kasagi were scrapped. Seven more Unryu class ships were added to the 1942 program, but they never got beyond the paper work.

The Japanese wartime carrier construction program, though ambitious, was not at all successful. What few successes they did enjoy were short-lived. Since the pressure was on—especially after the Battle of Midway—it was natural that they would turn to quick conversions. In this area, too, the results were discouraging. The submarine depot ships  Taigei, Tsurugisaki, and Takasaki were the first to be converted. They became the  Ryuho, Shoho and Zuiho. HIJMS Ryuho, one of only four Japanese carriers to survive WW II was converted from a 10,500 tons submarine depot ship, like Zuiho and Shoho.

Commissioned in 1943, Ryuho displaced 16,150 tons (full load) from a 215.8 x 19.6 x 66 metres (707.5 x 64.25 x 21.75 feet) hull. The four boilers and two shafts delivered 52,000 shp, giving maximum speed of 26.5 knots. With a complement of 875, the ship carried 30 aircraft and eight 127 mm (five inch) guns. Employed chiefly as an aircrew training carrier, Ryuho was called up to help repel the American invasion of Saipan. She emerged virtually unscathed, but like the other Japanese carriers in that action, she lost most of her aircraft and aircrew in the “Marianas Turkey Shoot”.

Ryuho’s structure was weak when she entered the yard for conversion. While being strengthened and given carrier characteristics, she was hit by several bombs from one of the B-25 bombers led by Jimmy Doolittle and launched from the USS  Hornet . This, of course, delayed completion. When conversion was completed, she displaced over 15,000 tons standard. She had a speed of 26.5 knots, was armed with eight 127 mm (five inch) guns, and accommodated 30 aircraft.  Ryuho saw much action, participating in the battles of the Philippine Sea and Leyte Gulf in 1944. In March 1945, she was moored at Kure, bombed by carrier-based USN aircraft and gutted by fires.

Shoho and Zuiho both displaced over 13,000 tons standard upon completion of conversion.  Zuiho was completed in December 1940, while  Shoho was completed nearly two years later. Both had a speed of 28 knots, were armed with eight 127 mm (five inch) guns, and accommodated 30 aircraft.

Coral Sea

Shoho’s first battle was her last: she was sunk by carrier-based aircraft of the Lexington and Yorktown on 7 May 1942, during the Battle of the Coral Sea. Zuiho was not much luckier. Her contributions to the Battle of Midway and the Aleutians campaign were negligible. At the Battle for Leyte Gulf, she was sunk by carrier-based aircraft.

The conversions of the Ise and Hyuga from battleships proved to be one of the most puzzling experiments undertaken by the Japanese after the Battle of Midway. Their aft turrets were removed and abbreviated flight decks were installed. A large hangar, an elevator, and two catapults were added, permitting the ships to launch all their aircraft in 20 minutes.

HIJMS Ise  (above) and Hyuga (below) were WW I-era battleships of 38,700 tons with 12 x 356 mm (14 inch) guns in six twin turrets. After Midway, they were converted into hybrid aircraft carriers with a hangar and two catapults. Their designated wheeled dive bombers, Asahi D4Y1 Model 11 Suisei (Judy) never arrived, but the ships operated a few seaplanes.

The planes scheduled for these ships were sent to Formosa (now Taiwan) before the ships were completed. The conversions were employed in the Battle of Leyte Gulf. By this time, Japan had run out of aircraft to supply them, and the ships were used solely in their capacity as battleships. They were later sunk, in July 1945, by USN carrier-based planes.

Another conversion, that of the Ibuki from an improved Mogami class cruiser, also had a rough time of it. She was authorised under the 1941 program but shortly after her launching in May 1943, work on her was halted for six months while authorities haggled with the possibility of reconverting her into a fast oil tanker—much needed by the Japanese navy. The decision made, work renewed, this time at a furious pace. Four of her eight boilers were pulled out and this space used for the storage of fuel oil. A hangar and two elevators were installed, and a bridge was placed on her starboard side. She was capable of 29 knots and could carry 27 aircraft. But work stopped again, this time when the construction of small submarines took priority in the shipyards. She was never finished; at the end of the war the  Ibuki was scrapped.

The most ambitious conversion and the most disappointing career was that of the Yamato class battleship  Shinano. Laid down as a battleship but not completed when hostilities broke, the possibility of converting her to a carrier was entertained. This possibility became a necessity after the Battle of Midway. Survivors of this battle pointed out serious deficiencies in carrier construction and designers at the Naval Technical Bureau listened well. Heavier armoured flight decks were needed to protect them from dive-bombing attacks. Fuel and ammunition stowage spaces needed redesign.

“Hotel ship”

Originally, plans for the conversion of the Shinano called for her to act as a “hotel ship,” supporting land- or other carrier-based planes; she was not to carry aircraft of her own. This plan was changed and by September 1942 the new design was completed and construction began. Shinano, basically, was to be a CVB. Heavy emphasis was placed on armour. Large bulges below the waterline were to minimise torpedo damage. At the waterline, a 203 mm (eight-inch) thick belt of armour was retained. Another 102 mm (four-inch) thick armoured deck had already been installed before conversion started and this deck became the hangar deck.

Rolling metal curtains opened up the forward two-thirds of this deck for night operations and rough seas. The remaining third was closed completely when the curtain was rolled into place. Her flight deck and elevators were designed to withstand 454 kg (1000 pounds) bombs. With this weight,  Shinano displaced 68,000 tons during her trials at sea.

USS Redfish SS-395 helped to put the carrier Junyo out of the war and sank the carrier Unryu. Allied carrier-borne aircraft, along with submarines, defeated Japan’s Pacific Ocean primary war machine: the aircraft carrier.

The Battle of Midway also called attention to the ship’s ventilation system. All ducts were protected with 38 mm (1½ inch) armour. Wood was eliminated from the ship wherever possible. A fire-resistant paint was introduced, and a foam fire-extinguishing system was installed. The carrier was launched on 5 October 1944 and commissioned 19 November. On the 28th, yard workers still aboard and crewed by green hands, she got underway for Kure where the air complement was to board.

Carrier aviation rout

It was at this point that USS  Archer-Fish picked her out on radar while surfaced. The submarine chased the zig-zagging force and waited until the carrier and her three-destroyer escort crossed her line of fire. At 0315  Archer-Fish fired six torpedoes; four hit the carrier. Slowly, she flooded and listed. At 1018 28 November, all hands were ordered to abandon ship. A few minutes later,  Shinano capsized and sank—with half her crew still aboard.

For many in the Japanese Navy, the powerful  Shinano was the last hope. With her sinking, Japanese carrier aviation died, never to operate again.