An error in IJN CV capacities?

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Local Yokel
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An error in IJN CV capacities?

Post by Local Yokel »

I am having a problem with Japanese aircraft carrier capacities. This may be due to confusion on my part about how reserve aircraft are dealt with, but might also be the product of an error in the capacities attributed to some of the carriers.

My difficulty stems from the fact that the scenarios I’ve looked at attribute a capacity of 71 aircraft to Hiryu and 72 aircraft to Kaga, which suggests that these two ships had substantially the same aircraft operating capability.

However, it seems to me that these figures credit Hiryu with too great a capacity and Kaga with one that is too small. Reputable sources attribute to Kaga a capacity of 91 aircraft including part-dismantled spares, whilst for Hiryu I have a source suggesting a capacity of 57 aircraft and 16 spares. However, I suspect this source understates Hiryu’s capability.

The Pearl Harbor OOB at the Navweaps site indicates that on 7 December 1941 Kaga despatched a combined total 27 attack planes, 27 carrier bombers and 18 fighters in the two attack waves, whilst retaining 9 fighters on CAP: 81 aircraft in total. From this I deduce that she had an operating capability of 81 modern aircraft. Taken in conjunction with the 91 aircraft total capacity usually attributed to her, this implies that she could carry a total of 10 spares in addition to her operational aircraft.

For Hiryu, the Navweaps OOB indicates that at Pearl Harbor she launched 18 attack planes, 18 carrier bombers and 15 fighters, retaining 9 fighters on CAP – a total of 60 aircraft. For Soryu, a carrier of similar size, the corresponding figures are 18, 18, 18 and 9, giving 63 aircraft in total.

It seems to me that one of the game’s capacity figures for these ships must be wrong. Using current game capacities, enlargement of Kaga’s hikokitai by the permitted maximum of 15% before air ops become impossible brings her operational capability up to 82 aircraft – one better than for the Hawaii Operation but with no remaining capacity for spares. But if you do the same with Hiryu, you raise her operational capability to a historically unfeasible 81 aircraft!

I am not clear as to how reserve aircraft in a carrier air unit affect that carrier’s capacity to operate aircraft. If reserves are counted in the number of aircraft embarked, then it seems to me that Kaga should be attributed a capacity of 91, permitting the historical complement of 81 aircraft plus up to 10 reserves. Hiryu should be treated as being equivalent to Soryu and have a capacity of not less than 71, so that she, like Soryu, can operate 63 aircraft and carry 8 to 10 reserves. However, if reserve aircraft do not count towards the carrier’s capacity, then Kaga’s capacity should be increased from 72 to 81, and Hiryu’s reduced to 63 – the same as for Soryu at present.
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herwin
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RE: An error in IJN CV capacities?

Post by herwin »

See this thread.

Each carrier is rated for CAP/Strike/Hanger/Reserve. CAP is the space available for fighters on deck alert while still allowing landings and launches. Strike is the space on which a deck load strike can be marshalled and still launch. Hanger is the space available for aircraft in the hangar. Reserve is the space available for partially disassembled aircraft. Effective carrier capacity is CAP+Hangar, with some weather risk and corrosion damage to the aircraft on the flight deck. Navies that didn't want to waste aircraft stuck to Hangar capacity. TheElf can probably criticise, but I was working with material available in the open literature 30 years ago.

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RE: An error in IJN CV capacities?

Post by Pascal_slith »

Dallas Isom in "Midway Inquest" indicated the complete launch schedule of the 6 carriers for PH.  These are laid on page 62 with note 50 for the chapter being important (Akagi's capacity was the same as Kaga but was reduced for the strike because it used space for fuel drums).  Hiryu and Soryu definitely had less capacity.  Can't go into the details just now.  I'll try copying it later.

I also suggest as sources "Sunburst" by Mark Peattie (of "Kaigun" fame) and "Titans of the Seas" by James and William Belote.
So much WitP and so little time to play.... :-(

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CV2
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RE: An error in IJN CV capacities?

Post by CV2 »

Don't forget you can operate 115% so with the 72 plane Kaga + 15% (10) = 82 aircraft.
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RE: An error in IJN CV capacities?

Post by Pascal_slith »

Here's the quote from Midway Inquest.

The nucleus of the Striking Force consisted of all six of Japan’s attack carriers:
Akagi (“Red Castle”) and Kaga (“Increased Joy”), Hiryu (“Flying Dragon”)
and Soryu (“Green Dragon”), and the new super-carriers Shokaku (“Soaring
Crane”) and Zuikaku (“Happy Crane”). They embarked 423 aircraft—405 “operational”
(that is, with pilots). Three hundred sixty planes were scheduled for
the attack on Pearl Harbor (note 49)—though only 355 would eventually be assigned
for the strike due to pilot disabilities—plus 45 operational planes for combat air
patrol, and the remaining 18 planes as “spares.” (The “operational” aircraft
complements appear to have been: 67 for Akagi,(note 50) 76 for Kaga, 57 for Hiryu, 56
for Soryu, 72 for Shokaku, and 72 for Zuikaku.) Supporting the carriers were the
two fast battleships Hiei and Kirishima, the heavy cruisers Tone and Chikuma
(which had been specially designed to carry five float planes each for reconnaissance),
and a screen of nine destroyers led by a light cruiser.

Here's note 50:

50. Akagi was designed to have the same aircraft capacity as Kaga, but for the Pearl
Harbor and Midway operations carried fewer planes. This was because its fuel oil tanks
were smaller than Kaga’s; to give it the same range, Akagi carried extra oil in drums,
which were stored in the lower hangar—reducing space for airplanes. Interview with
Tokayoshi Morinaga (torpedo plane pilot on Kaga), July 1993.
So much WitP and so little time to play.... :-(

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RE: An error in IJN CV capacities?

Post by Q-Ball »

ORIGINAL: Pascal

... to give it the same range, Akagi carried extra oil in drums,
which were stored in the lower hangar—reducing space for airplanes.

That sounds safe![:D]
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RE: An error in IJN CV capacities?

Post by VSWG »

What could possibly go wrong?! [:D]
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RE: An error in IJN CV capacities?

Post by DivePac88 »

Japanese figures (from translation by Tone),

AKAGI; as built 60, as reconstructed 91 (63 operational).

KAGA; as built 60, as reconstructed 91 (72 operational).

SORYU; 68 (57 operational).

HIRYU; 73 (59 operational).

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RE: An error in IJN CV capacities?

Post by JeffroK »

From Shattered Sword by Parshall & Tully

Akagi     91 total when recommisioned, 63 operational (approx) in 1941

Kaga      91 total when recommisioned, 72 operational (approx) in 1941

Soryu     68 total when commisioned, 57 operational (approx) in 1941

Hiryu      73 total when recomisioned, 59 operational (approx) in 1941

Dont forget that different aircraft occupy different amounts of space, so the shape & size of the airgroups affects the number of aircraft carried.
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Local Yokel
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RE: An error in IJN CV capacities?

Post by Local Yokel »

A big problem in any discussion of Japanese carrier capacities is that none of the available sources of information can be treated as dispositive. I guess there may be only one non-Japanese historian who can speak authoritatively about how many operational aircraft were embarked in any one of the carriers that attacked Pearl Harbor, and his book on the subject doesn’t seem likely to reach the shelves in less than a year from now. Even he has indicated that official records are beset with issues, in particular:

- there are a number of discrepancies between the Official War History aircrew roster for the Hawaii Operation and the air group records from which that roster has been derived;

- apparently there is no surviving air group record for the CAP flown from Kaga on 7 December.

FWIW the Official War History tabulates aircrew for 35 aircraft flown from Kaga in each of the two attack waves. If the Official History were to prove accurate to that limited extent, it means that on 7 December Kaga was operating a minimum of 70 aircraft committed to the attack itself, in addition to which she would have contributed an indeterminate number of carrier fighters to ‘garrison’ over Kido Butai itself. At the moment it looks as though no means can be found for establishing what that number was. 3? 6? 9? Even if the CAP contribution was confined to a single shotai of 3 aircraft that still makes Kaga’s total of operational aircraft larger than the approximation offered by Parshall and Tully.

My guess is that Dallas Isom may have got the figure of Kaga’s aircraft right at 76, if only because the retention of only one shotai of fighters for CAP over the task force is so perilously small a number, whilst the holding back of two three plane elements allows for relief and reinforcement of the standing patrol and a reserve against operational casualties. But I accept this is purely a guess.

I also accept that, due to increases in the size of aircraft embarked, Kaga’s maximum capacity may have shrunk somewhat from the figure of 91 at the time of her reconstruction. However, I find it hard to believe that this accounts a reduction of 19 in the number of aircraft that can theoretically be embarked – that’s a capacity loss of almost 20%!

In general, I see little here that is much at odds with my first thoughts that Kaga’s capacity in the game is understated whilst Hiryu’s is overstated. And I would still be grateful for clarification of whether reserves affect the total number of aircraft that can be embarked in a carrier.
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RE: An error in IJN CV capacities?

Post by herwin »

ORIGINAL: JeffK

From Shattered Sword by Parshall & Tully

Akagi     91 total when recommisioned, 63 operational (approx) in 1941

Kaga      91 total when recommisioned, 72 operational (approx) in 1941

Soryu     68 total when commisioned, 57 operational (approx) in 1941

Hiryu      73 total when recomisioned, 59 operational (approx) in 1941

Dont forget that different aircraft occupy different amounts of space, so the shape & size of the airgroups affects the number of aircraft carried.

The number of aircraft that could be operated depended on spot size. For pictures, see this link. What I did in my analysis thirty years ago was draw layouts of the various flight decks and hangar decks, allowing me to explore how many planes could fit in various operational scenarios with folded and unfolded wings. See Friedman for a discussion.
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RE: An error in IJN CV capacities?

Post by Sardaukar »

ORIGINAL: herwin

The number of aircraft that could be operated depended on spot size. For pictures, see this link. What I did in my analysis thirty years ago was draw layouts of the various flight decks and hangar decks, allowing me to explore how many planes could fit in various operational scenarios with folded and unfolded wings. See Friedman for a discussion.


I think you mean the number of aircraft that could be operated SIMULTANEOUSLY depends on spot size? As Friedman says, actual aircraft capacity carried little explicit weight. Usually "deck-load strike" is less than practical number of planes CV can operate. There is also the matter with elevator numbers and their position. So, CV could launch full deck strike and then start to spot for second, but we also have to allow some for maintaining CAP, unless there was designated CV for that. So calculations game-wise would be quite tricky, to fit with all probabilities. It's safe to say that no CV operated with absolute maximum of planes they could operate theoretically (maybe in ferry mission), because it was impossible in practice.

I think they made good compromise with historical figures fitted into AE game engine.
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RE: An error in IJN CV capacities?

Post by herwin »

ORIGINAL: Sardaukar

ORIGINAL: herwin

The number of aircraft that could be operated depended on spot size. For pictures, see this link. What I did in my analysis thirty years ago was draw layouts of the various flight decks and hangar decks, allowing me to explore how many planes could fit in various operational scenarios with folded and unfolded wings. See Friedman for a discussion.


I think you mean the number of aircraft that could be operated SIMULTANEOUSLY depends on spot size? As Friedman says, actual aircraft capacity carried little explicit weight. Usually "deck-load strike" is less than practical number of planes CV can operate. There is also the matter with elevator numbers and their position. So, CV could launch full deck strike and then start to spot for second, but we also have to allow some for maintaining CAP, unless there was designated CV for that. So calculations game-wise would be quite tricky, to fit with all probabilities. It's safe to say that no CV operated with absolute maximum of planes they could operate theoretically (maybe in ferry mission), because it was impossible in practice.

I think they made good compromise with historical figures fitted into AE game engine.

I think I agree. Flight deck operations were choreographed in detail within the constraints of flight and hangar deck layouts and aircraft planform. What I did was set up CAP operations to see how large those could be, and set up a deckload strike for that. I then packed the aircraft into the hangar layout to see what could be reasonably kept there. Reserves were from other sources. Typically, a deckload strike was half the aircraft complement.
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RE: An error in IJN CV capacities?

Post by John Lansford »

I thought the Japanese didn't spot planes on-deck until ready to launch, unlike the USN.  That reduced their operational tempo, and caused delays in launching whenever planes in the air had to land suddenly since any new planes to launch had to use the elevators to get on deck.  IJN carriers should be rated for plane capacity by the size of their hangars, not the size of their flight deck.
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RE: An error in IJN CV capacities?

Post by CV2 »

Or you could just rate them by how many planes they historically operated.
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RE: An error in IJN CV capacities?

Post by mike scholl 1 »

ORIGINAL: John Lansford

I thought the Japanese didn't spot planes on-deck until ready to launch, unlike the USN.  That reduced their operational tempo, and caused delays in launching whenever planes in the air had to land suddenly since any new planes to launch had to use the elevators to get on deck.  IJN carriers should be rated for plane capacity by the size of their hangars, not the size of their flight deck.


USN carriers could perform a "continuous launch" of their entire air groups because they could "run up the engines" of A/C in the hanger decks. The Japanese could not do this do to the design of their CV's. They had to spot a strike on deck, run up the engines, launch that strike, bring up another deckload of planes, run them up, and launch a second strike.
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RE: An error in IJN CV capacities?

Post by herwin »

ORIGINAL: John Lansford

I thought the Japanese didn't spot planes on-deck until ready to launch, unlike the USN.  That reduced their operational tempo, and caused delays in launching whenever planes in the air had to land suddenly since any new planes to launch had to use the elevators to get on deck.  IJN carriers should be rated for plane capacity by the size of their hangars, not the size of their flight deck.

That didn't mean they couldn't; just that they didn't. Aircraft left on deck were vulnerable to salt water corrosion and weather. The RN moved from keeping their aircraft below to a deck park during the war as aircraft became more available. The same option was available to the IJN.
Harry Erwin
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RE: An error in IJN CV capacities?

Post by Local Yokel »

Some support for Dallas Isom’s contention that Akagi took a reduced aircraft complement to Hawaii is to be found in the War History aircrew roster, to which I referred earlier. If correct, it reveals that Akagi despatched 33 aircraft in the first attack wave, and only 27 in the second. On the Isom figures that would leave 7 fighters for CAP over Kido Butai.

Morinaga’s recollection that Akagi was carrying extra fuel in the lower hangar is tantalising because it begs the question ‘which lower hangar?’ Did he mean the second level hangar or the third? The third hangar was very much smaller than the other two, but the most likely place for storage of additional fuel drums.

This leads conveniently to consideration of the Japanese carriers’ hangar area. Referring to Parshall and Tully’s Shattered Sword, Akagi is credited with 93,000 square feet for the upper and middle level hangars combined, and 8,515 square feet for the lower level hangar. For Kaga, the corresponding figures are 108,240 square feet and 5,568 square feet. Hiryu and Soryu had only two hangar levels; they lacked the small third level hangar of the bigger carriers. Parshall and Tully credit both Hiryu and Soryu with same overall hangar area: 61,740 square feet.

There’s no getting away from this: Hiryu and Soryu had only 66% of the hangar area of Akagi and 57% of that of Kaga – and that’s leaving out of account the additional space of the two big carriers’ third level hangar. Akagi’s hangar area was approximately 86% of that for Kaga. Yet, according to the capacity figures attributed to the carriers in the game, Kaga can accommodate only 72 aircraft against Akagi’s 81, notwithstanding her significantly larger hangars. Meanwhile Hiryu, with a hangar area only two thirds the size of Kaga, can accommodate only one fewer aircraft.

The number of aircraft in a deckload spot may be all very well as a measure of a carrier’s striking capacity, but overall capacity and the limit it places on total aircraft embarked has greater relevance to that ship’s ability to remain in a fight once attrition has started to take its toll. In the CHS version of WitP, Shokaku, Zuikaku, Kaga and Akagi were each given a capacity of 84 aircraft, whilst Hiryu and Soryu had capacities of 71 and 70 respectively. In AE these have been altered as follows:

Hiryu: no change
Akagi: -3
Soryu: -7
Kaga, Shokaku and Zuikaku: -12

It appears that something prompted the developers to make these reductions, but I can see no obvious rationale for them. In particular, it makes no sense to me that Hiryu, with only two-thirds of Kaga’s hangar area, should be treated as having substantially the same capacity. Even more inexplicable is a decision that Kaga, with bigger hangars than Akagi, should have her capacity reduced by four times the amount of Akagi’s reduction.

I would welcome an explanation of these reductions, and also one about the impact, if any, of reserve aircraft upon a carrier’s capacity.

<edit> Corrected spelling </edit>
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RE: An error in IJN CV capacities?

Post by herwin »

The spot size of an aircraft should be about wing span folded times length times about 2/3rds, except for the Grummans, which folded differently. For example, an A6M was about 36x30*2/3 = 720 square feet. Allowing that you couldn't pack them that close, 9 A6Ms occupied about 6600 square feet of hangar space. Vals took up about the same space, while Kates, with folding wings required about 5000 square feet of hangar space (9*25*30*2/3) for nine aircraft. At launch, the Hiryu could position 2 Kates, 2 Vals, or 2-3 Zeros in a row across the flight deck. With a minimum takeoff distance of about 250 (normal)-300 (overload) feet, and a flight deck length of 711 feet, a deckload strike would be 400-450 feet of aircraft arrayed in pairs. That works out to 10x2 attack aircraft and 5x(2-3) fighters. The Shokaku/Akagi/Kaga were good for two or three across and 500-550 feet of aircraft. Figure a range of 36-54 (average 45) aircraft in a deckload strike. American carriers were similar to the Shokaku. Landing distance was about 400 feet, so a standing CAP required 400 feet for landing, 250 feet for takeoff, and had perhaps 150 feet for aircraft operations on the flight deck.
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RE: An error in IJN CV capacities?

Post by mike scholl 1 »

ORIGINAL: herwin

ORIGINAL: John Lansford

I thought the Japanese didn't spot planes on-deck until ready to launch, unlike the USN.  That reduced their operational tempo, and caused delays in launching whenever planes in the air had to land suddenly since any new planes to launch had to use the elevators to get on deck.  IJN carriers should be rated for plane capacity by the size of their hangars, not the size of their flight deck.

That didn't mean they couldn't; just that they didn't. Aircraft left on deck were vulnerable to salt water corrosion and weather. The RN moved from keeping their aircraft below to a deck park during the war as aircraft became more available. The same option was available to the IJN.


Not quite the same, Herwin. The IJN didn't have the American Industrial Monster cranking out so many A/C that they could afford to scrap them if they were damaged by weather.
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