Machinery: 4 shafts each with generating turbines and 2 electric motors 16 White-Foster boilers working at 300psi 184,OO0shp delivering 34 knots
Armament: 4 twin Sin; 12 single 5in
Protection: 6in waterline belt; 6in bulkheads; 3in main deck; 1 to 3in lower deck; turrets up to 3 in; barbettes 6in
Fuel: 9,748 tons FFO
Endurance: 6,960 miles at 20 knots
Complement: 2,122
Aircraft operating data
Flight deck: 880ft × 90ft
Hangar: 393ft × 68ft × 20ft
Catapult: single Norden flywheel type. soon removed, 6,0001b at 40 knots
Arrester wires: 8 hydraulic, 8,0001b at 60 knots; 1 barrier as built
Lifts: fwd 29ft 5in long × 59ft 5in wide aft 29ft 3in long × 34ft 1 lin wide
Aircraft: 90
Aircraft fuel: 110,140gal
Air weapons: torpedoes; bombs; 0.5 in and 0.3in machine-gun ammunition; flares and pyrotechnics
The USS Saratoga, CV-3, photographed from Victorious. (AUTHOR’S COLLECTION)
The Imperial Japanese Navy
boilers in six boiler rooms.
Hosho as built, with a small starboard-side island. (AUTHOR’S COLLECTION)
Apart from the altered machinery, the original tanker hull was modified only by the trunking of the boiler uptakes to three funnels at the starboard deck edge amidships, which were lowered to the horizontal during flying operations. Four 5.5in guns were mounted outboard of the hangar, together with several machine guns. The former upper deck became the hangar deck and the sides were continued up to the flight deck for two-thirds of the ship’s length to make it semi-enclosed. The extra top weight was compensated for by a Sperry stabilisation system which worked well. The flight deck was supported by the hangar walls and pillars fore and aft. It was made of mild steel covered with wooden planking laid fore and aft, and was originally stressed to take aircraft weights up to 8,800lb.
This was later increased to 13,200lb, with lifts and the six arrester wires eventually fitted stressed to the same figure. Sections of the hangar sides amidships were left open to provide ventilation but, with the hangar deck only 15ft above the waterline, heavy seas could wash down the hangar deck, and they were soon plated in.
Akagi in the summer of 1941. Her small port-side island and the tapered stern make it difficult to work out which way she
is heading. (AUTHOR’S COLLECTION)
She was originally completed with a small island comprising a bridge over a charthouse on the starboard side amidships but, with a deck only 59ft wide, pilots who carried out the initial flying trials warned that it was dangerous and it was immediately removed. The bridge arrangements were changed to wing platforms on either side of the forward end of the hangar ‘box’ and the charthouse was repositioned between the pillars supporting the forward overhang of the flight deck. Unlike the RN and USN, the IJN did not develop a system using ‘batsmen’ to control aircraft approach, but installed light projectors using red/amber/green lights at set angles to show pilots whether they were low, correct or high relative to the ideal glide slope.
After extensive use as a prototype operational carrier, Hosho was used mainly on training duties during the Second World War, although she did see action in the Midway operation. Unlike the majority of IJN carriers she survived the war and was used for a while on repatriation transport duties, extracting Japanese forces from island garrisons after VJ-Day. She was scrapped at Osaka in 1947.
Hosho technical details
Displacement: 9,630 tons deep load
Dimensions: length 551ft 4in beam 59ft 1 in draught 20ft 3in
Machinery: 2 shaft Parsons geared turbines 12 Kampon boilers 30,000shp delivering 25 knots
Armament: 4 single 5.51in; 2 single 3in plus 7.7mm machine guns
Protection: None
Fuel: 550 tons FFO
Endurance: Approximately 3,000 miles at 14 knots
Complement: 550
Aircraft operating data
Flight deck: 519ft × 59ft
Hangar: 423ft 6in × 55ft maximum reducing to 40ft by funnel uptakes × 14ft
Arrester wires: 6 × 8,8001b at 60 knots when completed
Lifts: fwd 44ft 11 in long × 36ft lin wide aft 42ft 4in long × 27ft 10in wide
Aircraft: 21
Aircraft fuel: approximately 50,000gal in bulk stowage
Air weapons: torpedoes; bombs; 20mm cannon and 7.7mm machine-gun ammunition; flares and pyrotechnics
Akagi
As in the RN and USN, the IJN elected to convert surplus battlecruiser hulls into aircraft carriers after the abandonment of capital ship construction agreed in the Washington Naval Treaty. Two incomplete hulls, Akagi and Amagi, were selected, but the latter was badly damaged by an earthquake while still on the slipway at Yokosuka in 1923 and her place was taken by the incomplete battleship Kaga.
Work on reconstructing Akagi, which translates as ‘Red Castle’, began in 1923 and she was completed on 25 March 1927. She had no island, a flight deck 632ft long and two hangars, one above the other, as in contemporary British carrier designs. Like the American battlecruiser conversions, a
small hangar was built in under the main ones for the stowage of dismantled spare aircraft. Only 213ft long by 40ft wide, it could be accessed only by the after lift. The small flying-off decks were taken a stage further, however, with one for each hangar; the deck forward of the upper hangar was 60ft long and intended for fighters, and the deck forward of the lower hangar was 160ft long and intended for heavier aircraft. Neither proved successful, and both were removed in 1936 when she was refitted with a full-length flight deck and a third lift forward to give access to the extended hangar. A small port-side island was fitted at the same time, intended to facilitate left or right circuit patterns when carriers operated in close proximity. Like many Japanese warships of the period in which she was designed, her boilers were intended to operate with both domestically produced coal and FFO. After her 1936 reconstruction only FFO was used, despite the difficulty and expense of its procurement.
Uptakes from the nineteen boilers were taken to one large funnel exhausting the smoke downwards on the starboard side amidships and a second, smaller funnel that exhausted upwards under the flight deck. Like the USN, the Japanese sought to protect these ships against cruisers, and 8in guns were fitted, six aft in casemates that proved difficult to use and four others in two twin turrets, one either side of the upper flying-off deck. The latter were removed during the 1936 refit when, in addition to lengthening the flight deck, the hangars were extended forward by 80ft.
Six electrically operated arrester wires were fitted initially, but were later replaced by nine hydraulically actuated units. No Japanese carrier was ever fitted with catapults. All IJN carrier-borne aircraft were capable of free take off and, unlike the British and American navies, seaplanes were operated from cruisers, freeing the carriers to operate nothing but fighters and strike aircraft. Akagi’s powerful machinery gave her a speed of just over 31 knots on trials. She was actually considerably heavier than the declared standard tonnage of 26,900, and when she recommissioned in 1938 her standard displacement was admitted to have risen to 36,500 tons despite the removal of the two heavy 8in gun turrets. Full-load displacement was 42,700 tons. There was no horizontal armour to protect the machinery or the poorly designed avgas stowage arrangements.
Akagi was lost on 4 June 1942 during the Battle of Midway, when she was hit by dive-bombers from the USS Enterprise. Fuelled and armed aircraft on deck and in the hangar exploded and started serious fires and, although she continued to steam and float at first, the spread of fires forced the machinery spaces to be abandoned. The consequent loss of power meant that the fires could not be brought under control and she had to be abandoned and scuttled.
Akagi technical details
Displacement: 34,364 tons deep load
Dimensions: length 857ft beam 95 ft draught 26ft 6in
Machinery: 4 shaft Gijitsu Honbu geared turbines 19 Kampon boilers 13 1.000shp delivering 31 knots
Armament: 2 twin 8in turrets on upper flying off deck; 6 twin 4.7in on sponsons
Protection: 6in waterline belt; 3.1indeck over machinery
Fuel: 3,900 tons FFO; 2,100 tons coal
Endurance: 8,000 miles at 14 knots
Complement: 1,600
Aircraft operating data
Flight deck: 562ft × 95ft. Flying-off decks 160ft long at hangar deck levels
Hangars: upper 354ft × 62ft (maximum) × 15ft lower 492ft × 59ft (maximum)x 15ft
Arrester wires: 6 electrically controlled. 13,2001b at 78 knots
Lifts: fwd 38ft 6in long × 42ft 8in wide aft 42ft long × 29ft 6in wide
Aircraft: 60
Aircraft fuel: 100,000gal, approximately, in bulk stowage
Air weapons: torpedoes; bombs; 20mm cannon and 7.7mm machine-gun ammunition; flares and pyrotechnics.
Smoke emerges from Kaga’s distinctive starboard, downward-tilted funnel. (AUTHOR’S COLLECTION)
Kaga
Kaga, named after a former Japanese province, differed in that she was laid down as a battleship.
She was 62ft shorter than Akagi and her less-powerful machinery gave her a trial speed of only 27 knots. The hangars were carried further aft and were slightly wider, which meant that she was able to operate an air group of about the same size. Her funnel arrangements differed in that they were divided into port and starboard trunkings which were led aft down the outside of the upper hangar a distance of about 300ft to exhaust over the quarterdeck; an unsuccessful system very like that used in the rebuilt British Furious. To minimise the use of oil, which was expensive to import, her boilers were originally designed to burn both coal and FFO, but after her 1934 refit they were all modified to burn oil only.
Like Akagi she originally had two flying-off decks, but these were removed after 1934 when the flight deck was extended over the entire length of the hull and the hangars extended forward. The two 8in gun turrets were similarly removed, but in one sense her refit was more extensive than that of her contemporary; the hull was cut abaft the hangar and a new 34ft section inserted to preserve the length- to-beam ratio after anti-torpedo bulges were fitted outboard of the hull. New machinery of 127,400shp replaced the original 91,000shp units, giving a greater top speed of 28.5 knots. Deck strength, arrester wires and lifts were all designed to handle aircraft up to 13,200lb. She was the first Japanese carrier to be built with a permanent island on the starboard side amidships, like those in British and American carriers.
Kaga was also lost in the Battle of Midway on 4 June 1942, when she was hit by four 1,000lb bombs from the USS Enterprise’s dive-bombers. These burst through the unprotected flight and hangar decks as they exploded, causing extensive fires. Abandoned soon afterwards, she blew up and sank nine hours later when fire reached her avgas tanks. Eight hundred of her ship’s company were lost.
Kaga technical details
Displacement: 33,693 tons deep load
Dimensions: length 782ft 6in beam 97ft draught 26ft
Machinery: 4 shaft Brown-Curtis geared turbines 12 Kampon boilers 91,000shp delivering 27.5 knots
Armament: 2 twin Sin turrets on upper flying off deck; 6 single Sin in casemates aft; 12 single 4.7in plus several machine guns
Protection: 6in waterlinebelr. 1.5in deck over magazines
Fuel: 3.600 runs FFO; 1.700 tons coal
Endurance: 8,000 miles at 14 knots
Complement: 1.340
Aircraft operating data
Flight deck: 560ft × 97ft
Hangars: Upper 415ft × 65ft × 15ft lower 470ft × 75ft × 15ft
Arrester wires: 6 × 13.200lb at 78 knots
Lifts: fwd 37ft 8in long × 39ft 5in wide aft 35ft long × 52ft wide
Aircraft: 60
Aircraft fuel: 100.000gal avgas in unprotected bulk stowage
Air weapons: torpedoes; bombs; 20mm cannon and 7.7mm machine-gun ammunition; flares and pyrotechnics
Béarn at speed, following the French battle-line. (AUTHOR’S COLLECTION)