![](\"\/photos\/Junyo_BG.jpg\")
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![\"Japanese](\"https:\/\/dbodesign.com\/images\/flags\/jap.jpg\")
<\/a> Japan, 1938-45: IJN Jun’y\u014d, Hiy\u014d <\/strong>![\"Hiyo](\"\/photos\/Japanese_aircraft_carrier_Hiyo.jpg\")
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Jun\u2019y\u014d (\u96bc\u9df9, \u201cPeregrine Falcon\u201d) and Hiy\u014d (\u98db\u9df9, \u201cFlying Hawk\u201d) were two Hiy\u014d-class aircraft carriers of the Imperial Japanese Navy (IJN). They were started before the war as the passenger liner Kashiwara Maru and Izumo Maru, respectively, but both were purchased by the IJN in 1941 while still under construction. They were both converted into aircraft carriers based on similar designs due to their common base.<\/span><\/p>\n Completed in May and July 1942, they participated in many Japanese Pacific offensives and campaigns, in the Aleutians, Guadalcanal, New Guinea, the Solomon Islands, and the Battle of the Philippine Sea (where Hiy\u014d was sunk). Lacking both aircraft and pilots, Jun\u2019y\u014d by late 1944 was used as a transport, was torpedoed twice, and was under repairs until March 1945 when they were cancelled and she was BU after the war. Note that some authors who speak of the Jun\u2019y\u014d class classify them as \u201cescort carriers\u201d.<\/span><\/p>\n hese two vessels started existence as the fast luxury passenger liners Izumo Maru and Kashiwara Maru ordered by Nippon Yusen Kaisha, or the Japan Mail Steamship Company, in late 1938. At the time, multiple civilian ships were being put into a “shadow factory” scheme where they would be converted down the line, and thus the Nippon Yusen Kaisha made an agreement with the IJN: In exchange for funding 60% of the construction costs they had to be designed in order to facilitate a conversion to aircraft carriers later. This was not an ad hoc, desperate wartime measure but rather a planned requisition.<\/span><\/p>\n The conversion of liners was not new at the time: HMS Argus showed the way in 1918: She was the former Italian liner Conte Rosso built at Beardmore, was requisitioned during the war and converted into a carrier, commissioned in September 1918, shortly before the hostilities ceased. At the time this demonstrated to all navies the potential of such ships for such conversions. In WW2, Italy converted two former liners as fleet aircraft carriers, creating the <\/span>Aquila class<\/b><\/a>, though they were not fully completed. Other nations would also attempt similar conversions, with varying levels of success.\u00a0<\/span><\/p>\n The basic design of the Izumo Maru class, therefore, was planned from the beginning with a set of features facilitating the later conversion process. Unlike common liners, they had a double hull, extra fuel oil capacity, and provisions to fit additional transverse and longitudinal bulkheads for protection. They also fitted extra bracing to support the deck and were given a longitudinal bulkhead separating the turbine rooms in case of flooding. Steel frames were provisioned also to support the future flight deck, and there was extra room between decks for a future hangar.<\/span><\/p>\n Also, a rearrangement of the superstructure and passenger accommodations was made in order to facilitate the future installation of aircraft elevators. There was also more space in between walls for future additional wiring. They were given a bulbous bow, known to increase speed but seldom used on civilian designs, alongside extra fuel tanks buried deep within for aviation gasoline storage, placed aft of the machinery spaces.<\/span><\/p>\n The only proper requirement of the Japan Mail Steamship Company was a top speed of 24 knots (44 km\/h; 28 mph) in order to save fuel, but the Navy indicated they were only satisfied with no less than 25.5 knots (47.2 km\/h; 29.3 mph) in order to ensure fleet operations. The compromise was to limit performance for the turbines installed, with a governor at 80% of maximum power for peacetime use.<\/span><\/p>\n Both ships were laid down in military shipyard in order to ensure this \u201cmilitary grade\u201d readiness: SS Kashiwara Maru at Kawasaki Shipyard, Kobe on 30 November 1939, and SS Izumo Maru at Mitsubishi Shipyard, Nagasaki on 20 March 1939. She was the lead vessel but was launched two days after her sister ship, although converted and completed sooner. This way, given the usual conventions, the class is not called Junyo but Hiyo.<\/span><\/p>\n Both were purchased on 10 February 1941, four months before launch, by the Navy Ministry at a final cost of \u00a548,346,000. With extra costs coming from their newly added armament and provisions for aircraft equipment, plus telemeters and fire control systems, for a supplementary cost of \u00a527,800,000 and global, for the two, of \u00a538,073,000 and \u00a5114,219,000 including their first aviation park. SS Kashiwara Maru and Izumo Maru were renamed, and provisionally became No.1001 (Dai 1001 bankan) and No.1002 (Dai 1002 bankan) to keep work secret. The name Jun\u2019y\u014d (Peregrine Falcon) and Hiy\u014d (Flying Hawk) were later chosen in accordance to the allegoric flying beasts naming convention for aircraft carriers at the time.<\/span><\/p>\n The admiralty however did not have them classified as fleet carriers due to their still insufficient speed but rather as auxiliary aircraft carriers (Tokusetsu kokubokan). However after the loss of four carriers at Midway (Kaga, Akagi, Hiryu; Soryu) in order to beef up the 1s Fleet air force and waiting for additional proper fleet carriers (notably the Unryu class), they were redesignated as regular carriers (Kokubokan) in July 1942, at about the time IJN Hiy\u014d was completed.<\/span><\/p>\n As completed, both vessels added a flight deck to the original hull and a large command island and funnel on the port side. The hull measured in the end 219.32 meters (719 ft 7 in) overall for an unchanged beam of 26.7 meters (87 ft 7 in) and 8.15 meters (26 ft 9 in) draft at normal load. Standard displacement was 24,150 metric tons (23,770 long tons) and the crew ranged from 1,187 to 1,224 officers and ratings.<\/span><\/p>\n Both liners had been fitted with two Mitsubishi-Curtis geared steam turbine sets. Together they produced a combined output of 56,250 shaft horsepower (41,950 kW). They drove 5.5-meter (18 ft) propellers at the end of the shafts. Steam came from six water-tube boilers which differed due to their separate building yards: Jun\u2019y\u014d had Mitsubishi three-drum models working at 40 kg\/cm2 (3,923 kPa; 569 psi) pressure and 420 \u00b0C (788 \u00b0F). IJN Hiy\u014d had Kawasaki-LaMont boilers (specs unknown).<\/span><\/p>\n Despite the fact that their machinery was designed for merchant service, it still was four times better than the military-grade and purpose-built <\/span>IJN Hiry\u016b<\/b><\/a> !<\/span><\/p>\n The latter indeed managed 153,000 shp but on 17,300 long tons, and 34.3 knots (64 km\/h; 40 mph). Her ratio and displacement were indeed completely different, she notably had a 7.84 m (30 ft)draft and only 22.32 m (73 ft) width.<\/span><\/p>\n The Hiyo class had a designed speed of 25.5 knots, and on trials, they managed to exceed them, but just. With 4,100 metric tons (4,000 long tons) of fuel oil onboard, their range reached 11,700 nautical miles (21,700 km; 13,500 mi) at 18 knots (33 km\/h; 21 mph), which was quite honorable, in fact, far better than the Soryu, Hiryu, Zuikaku class, or Kaga-Akagi on that matter. These numbers were due to their amazing propulsion design, more impressive due to the economic nature of the engines, not tailored for speed.<\/span><\/p>\n Their main feature was two superimposed hangars, like Ryujo and Ark Royal. Each was 153 meters (502 ft) long for 15 meters (49 ft 3 in) in width only, but 5 meters (16 ft 5 in). The difference in the width was explained by all the crew quarters and stores being installed on both sides of the hangar.<\/span><\/p>\n For fire safety, each hangar was subdivided into four sections which were split by fire curtains on rails. They could be deployed at a moment’s notice. These sections were also equipped with fire-fighting foam dispensers on either each side, but not sprinklers. The air group was managed in between these two levels and the deck, by two equal size square (with round corners) elevators 14.03 meters (46 ft 0 in) long and wide.<\/span><\/p>\n Maximum capacity was 5,000 kilograms (11,000 lb), compatible with most IJN aircraft in service at the time. They reached the deck, from the lowest level, in just 15 seconds. The ships had no catapult just like other IJN carriers, and planes landed by catching one of the nine electrically operated Kure type model 4 arresting gears. Two main Type 3 crash barricades were also installed at the main island level. For downed planes, boat service, or seaplane operations, a crane was installed on the port side of the flight deck, next to the rear elevator, which could be collapsed flush with the flight deck if need be.<\/span><\/p>\n Protection<\/span> Being a civilian ship nevertheless, it was difficult to \u201cload\u201d the design with heavy armor, and notably due to their role, a more minimalistic approach was chosen, to protect vitals, and against aviation fire mostly: They had no belt but an armored deck 2\u2033 thick (50 mm) plus an extra 0.8\u2033 (20 mm) plating over of ducol steel over the machinery, and 1\u2033 (25mm) box protection for their magazines and aviation fuel, also of made of ducol steel. This was insufficient to block a bomb penetrating the hangar but it could at least stop bomb fragments from penetrating the vitals. Against torpedoes, however, apart from the double hull and some compartmentation including the machinery spaces being subdivided by transverse and longitudinal bulkheads to limit flooding, no particular measures had been taken. Junyo would pay for it dearly in 1944. By March 1944 however, aircraft fuel tanks on the surviving Junyo had received additional concrete protection.<\/span><\/p>\n By its composition, both ships’ armament was a classic mix between the two standards of any IJN aircraft carrier of the time: Twin 5-in guns Type 89 dual purpose (DP) guns and triple 25 mm Type 96 AA mounts. The latter was augmented drastically until June 1944, mostly with single mounts.<\/span><\/p>\n These 40-caliber 12.7 cm Type 89 anti-aircraft (AA) guns in twin mounts were located on six sponsons along the sides of the hull, supported by pillars. There were two forward at the same level, and because of the island, one opposite it, to port, another aft, just before the rear elevator, and two starboard after the island.<\/span><\/p>\n They were also located on sponsons along the flight deck, four on the port side, opposite and aft of the island, and four starboard, behind the aft 5-in DP guns and at the level of the rear elevator.<\/span><\/p>\n The issues with the guns were known: They had no suitable targeting system, vibrations, and reloading was labor intensive due to the frequent need to change the fifteen-round magazines. In 1943, four additional triple mounts of the 25mm\/60 96-Shiki AA guns and two twin ones were added on both vessels. By March 1944, Junyo had seven extra triple 25mm\/60 and 18 single 25mm\/60 Type 96. In August 1944, twelve triple 25\/60 96-Shiki, and six 28-tubes 120mm AA Rocket Launchers were also added.<\/span><\/p>\n They were completed in May-August with no radar, but this was provisioned for in the design. During their late 1942 overhaul, both were fitted with the 1-Shiki 2-go early warning radar, mounted on their bridge\u2019s roof. In 1943, they kept the 1-Shiki 2-go radar, but a second was added aft of the flight deck, at the level of the rear elevator and on the port side, opposite the island.<\/span><\/p>\n By August 1944 the surviving IJN Junyo was given a 3-Shiki 1-go radar, replacing the one fitted on the bridge\u2019s roof.<\/span><\/p>\n In addition to a main telemeter for their main artillery installed on the bridge and another installed on a structure forward of the island, they had extra side safety nets, mostly installed alongside the aft part of their flight deck, starting at the island port and starboard, and ending at the level of the aft lift. They were mounted on elevating frames, two to port and three to starboard. For communications, they had a main tripod mast aft of the island, behind the funnel, a main radio mast just aft the funnel, and two derrick antennae for long-range communication on the side of the flight deck, on both the port and starboard side on sponsons.<\/span><\/p>\n The flight deck landing lip was beveled and painted in the standard red and white band pattern. On both sides were installed sets of lights to help the pilot figure out his position and balance his landing approach. Another marking this time with direction indicators (painted white) was set in between the crashing barriers at the island level for the long launching spot and at the end of the flight deck, which was clad in metal plating while the rest of the ship, to the exception of the landing area, was wooden-sheathed. Space aboard was limited. Two \u201cvals\u201d, wingtip to wingtip, covered the entire beam, making parking difficult.<\/span><\/p>\n The ships also carried several service boats: Two diesel-powered cutters aft, under the landing deck in an open space and able to be reached by the aft cranes. The ship also carried a small yawl under davits under the side deck close to the island, and another on the port side, opposite the island, but the rest of the ship’s complement comprised inflatable rafts installed wherever possible. The ships carried four paravanes for mine cutting, stored close to the bow where they were fitted, on either wall of the forward hangar section. Two static anchorages with extra anchors were located close to the bow. There were side ladders to mount\/dismount small boats on the starboard. For stability, they were both fitted with anti-rolling bars underwater.<\/span><\/p>\n Technically, these vessels could carry 54 aircraft, which was honorable but was less than the Zuikaku class, which carried 72, or the Hiryu and Soryu which carried 64 and nine spares, despite their smaller size. This was expected however due to the limited width of the hangars. When completed in the summer of 1942 they were given the \u201cclassic trio\u201d of the time: <\/span>A56M \u201cZero\u201d fighters<\/b><\/a>, <\/span>D3A1 diving bombers<\/b><\/a>, and <\/span>B5N torpedo bombers<\/b><\/a> (\u201cZeke\u201d, \u201cVal\u201d and \u201cKate\u201d in allied code). The exact composition varied over time and ship.<\/span><\/p>\n As completed, Junyo had 16 <\/span>A6M2 \u201cZeke\u201d<\/b><\/a> fighters (which replaced the planned 12 A5M plus four in storage) and 18, later 24 D3A (40) plus either spare and nine \u201cKates\u201d, which were nine in July, for 21 \u201cZeke\u201d so 48 total, plus probable spares.<\/span><\/p>\n Hiyo had 21 \u201cZeke\u201d, 18 D3As, and 9 B5Ns when completed in August, but in early 1943, she carried 27 fighters and 12 torpedo bombers only.<\/span><\/p>\n In November 1943, Junyo received its first 12 A6M5, in compliment to her 12 A6M2s. The rest of her air group comprised nine D3A2 \u201cVal\u201d completed by nine D4Y \u201cJudy\u201d and nine B5N making 51 aircraft.<\/span><\/p>\n IJN Hiyo retained her A6M2s into late 1943, but in June, at the battle of the Philippines, she had nine of them plus eighteen A6M5, in complement of eighteen D3A2 \u201cVal\u201d and nine B6N. She never operated the D4Y contrary to her sister.<\/span><\/p>\n From June 1944 until she was torpedoed and sent back for repairs, she had nine A5M2, 18 A5M5 fighters, nine D3A2 \u201cVal\u201d and nine D4Y Suisei \u201cJudy\u201d and nine B6N Tenzan \u201cJill\u201d, both being for more capable than their predecessors. Her air group was sent to other carriers when she was sent back for repairs and never returned.<\/span><\/p>\n <\/p>\n Author’s illustration of IJN Junyo in 1944, battle of the Philippines <\/em><\/p>\n<\/div>\n<\/div>\nConversion genesis: From Liners to Aircraft carriers<\/h2>\n
<\/div>\n<\/div>\nPurchase and conversions start<\/h2>\n
![\"\"](\"\/photos\/Junyo_class__fql_full.jpg\")
\njunyo on navsrource.org<\/em><\/p>\n<\/div>\n<\/div>\nDesign of the conversion<\/h2>\n
Powerplant: Best range of any IJN carriers<\/h3>\n
![\"junyo-left-side\"](\"\/photos\/junyo-left-side.gif\")
\njunyo-left-side navsrource.org<\/em><\/p>\nFlight Deck and accommodations<\/h3>\n
![\"\"](\"\/photos\/Junyo_class__sml_full.jpg\")
\n-The flight deck as completed measured 210.3 meters (690 ft), thus slightly shorter than their overall length.<\/span>
\n-Maximum width was 27.3 meters (89 ft 7 in), better than most fleet carriers of the time, thanks to their larger beam.<\/span>
\n-The large island was positioned starboard and was overhanging from the side with a large, bulgy structure going down almost to the waterline.<\/span>
\n-The engineers managed something new with the exhaust system as they had truncated it from all the ship’s boilers into a single funnel and not over the side of the hull, below flight deck level as usual.<\/span>
\nThis innovation, with the funnel 26\u00b0 angled outwards, allowed a better smoke dispersal far from the deck and avoided \u201chot points\u201d close to the flight deck. Models already were tested with this shape and smoke proving this was not interfering with flight operations. It became a feature of many future IJN carriers.<\/span><\/p>\n<\/div>\n<\/div>\n
\n![\"IJN](\"\/photos\/ijn-hiyo-1942-aircraft-carrier.jpg\")
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\nIJN Hiyo detailed plan, 1942<\/em><\/p>\n<\/div>\n<\/div>\nArmament<\/h3>\n
![\"\"](\"https:\/\/www.naval-encyclopedia.com\/wp-content\/uploads\/2020\/08\/Nagato-class_127mm-AADP.jpg\")
\n5-in DP guns<\/em><\/p>\nSix twin Type 89 5-in (12.7 cm) DP<\/h4>\n
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Eight triple Type 96 25 mm AA<\/h4>\n
![](\"https:\/\/www.naval-encyclopedia.com\/wp-content\/uploads\/2019\/11\/25mmHotchkiss-Type96AA.jpg\")
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Electronics<\/h3>\n
Other features<\/h3>\n
![\"\"](\"\/photos\/Junyo_class__island_full.jpg\")
<\/p>\nAir Group<\/h3>\n
![](\"\/naval-aviation\/ww2\/japan\/aichi\/D3A\/aichi-D3A2-Junyo-65KKt-junyoJ44.png\")
\nAichi D3A2 “Val”, 65th Kokutai aboard IJN Jun’yo, June 1944.<\/em><\/p>\n![](\"\/naval-aviation\/ww2\/japan\/yokosuka\/D4Y\/Yokosuka-D4Y1-634KKt-JunyoAug44.png\")
\nYokosuka D4Y “Judy”, 634th Kokutai IJN Jun’yo, August 1944<\/em><\/p>\n![](\"\/naval-aviation\/ww2\/japan\/mitsubishi\/A6M\/Mitsubishi-A6M5b-652KKt-Junyo-Jun44.png\")
\nMitsubishi A6M5b “Zeke”, 652th Kokutai, IJN Jun’yo, June 1944<\/em><\/p>\n![\"junyo\"](\"https:\/\/www.naval-encyclopedia.com\/ww2\/images\/ships\/japan\/junyo.gif\")
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![\"\"](\"\/photos\/Junyo_class__ONI-schematic.jpg\")
![\"Tamiya's](\"\/photos\/kit-tamiya-junyo.jpg\")
![\"IJN](\"https:\/\/www.naval-encyclopedia.com\/images\/flags\/jap_r.jpg\")
IJN Hiyo<\/h2>\n<\/div>\n![\"\"](\"\/photos\/Junyo_moored_at_Sasebo_Japan_1945.jpg\")
<\/p>\n![\"\"](\"\/photos\/Junyo_anchored_at_Sasebo_26_September_1945_USMC.jpg\")
![\"\"](\"\/photos\/View_of_the_starboard_side_of_the_Japanese_aircraft_carrier_Junya_at_Sasebo_26_September_1945_USMC.jpg\")
<\/p>\n![\"\"](\"\/photos\/Junyo_Sasebo_on_26_September_1945.jpg\")
![\"\"](\"\/photos\/Aft_flight_deck_of_the_Japanese_aircraft_carrier_Junyo_at_Sasebo,_Japan_19_October_1945.jpg\")
![\"\"](\"\/photos\/Japanese_bomb_explodes_near_USS_Enterprise_Battle_of_the_Santa_Cruz_Islands_26_October_1942.jpg\")
![\"B5N_passes_USS_Northampton_Battle_of_the_Santa_Cruz_Islands_26_October_1942\"](\"\/photos\/B5N_passes_USS_Northampton_Battle_of_the_Santa_Cruz_Islands_26_October_1942.jpg\")
![\"Junyo,](\"\/photos\/Junyo-rear.gif\")