Aircraft carriers with double hangars

[Vlad]

I was somewhat bewildered when, some time ago, i discovered that the Akagi and Kaga aircraft carriers had two hangar decks. more recently, I discovered this to be true of the Zuikaku and Shokaku as well, and the Ark Royal.

My question is, which carriers did and did not have two hangar decks, and why?

I can understand the weight limitations with the armored box on Illustrious, but why did the USN not follow the same practice with the Yorktown and Essex classes? Did the Lex have two decks?

[Foeth]

Didn't most IN carriers have several aircraft decks? Even the tiny Chiyoda and Chitose had two hangar decks.

[Werner]

Victorious and several of her early sisters are single-decked.

I believe the same is true of Majestic and Colossus.

Before about 1942, the British ships were designed with 14 foot or less hanger clearance. After that date, they conform to the US standard of 17.5 feet minimum.

[Jack Ray]

The reasons for single, or double hangars were initially based on two schools. The first equated hangar capacity w/ aircraft capacity and did not initially employ deck parks (RN/IJN). The second used deck parks (USN) to permanently store some of the aircraft and relied on the hangars for spares, maintenance and some aircraft. The advent of armored decks had some influence on the equation, but the Brits and Japanese "solved" that problem with shallow double hangars. Double hangars can also influence a ship's stability like Ryujo. The most important aspect of the Hangar debate remains hangar depth. By limiting it too much, you also limit the size and quality of aircraft that can be operated.

British CV's

Double Hangar
Furious/Courageous
Ark Royal III
Indomitable (1.5 Hangar decks)
Implacable class
Unicorn
Ark Royal IV/Eagle

Single hangar
Argus
Eagle(?)
Hermes I
Illustrious class
Colossus/Majestic
Centaur/Hermes class
CVA 01
Invincible class
CVF(?)

Weren't all USN carriers single decked? What about Japan? It seems that they were all double decked except for Shinano and, perhaps, the less capable IJN and IJA conversions like Chuyo.

Others:

CDG, Clemenceau, Garibaldi and Aquila are single decked. Don't know about Bearn, Graf Zeppelin, the new Italian multi-purpose ship, or Russian CVs.

Jack

[Guest]

I was somewhat bewildered when, some time ago, i discovered that the Akagi and Kaga aircraft carriers had two hangar decks. more recently, I discovered this to be true of the Zuikaku and Shokaku as well, and the Ark Royal.

My question is, which carriers did and did not have two hangar decks, and why?

I can understand the weight limitations with the armored box on Illustrious, but why did the USN not follow the same practice with the Yorktown and Essex classes? Did the Lex have two decks?

The Japanese carrier had extremely lightly built, non-structural hangers, almost a barn sitting on top of a hull. When hit, Japaneses carrier hanger sides literally blow out like a tin sheets. Kaga's hanger was said to be completely blown out down to the hull, with just the front and back ends of the hanger still standing, and almost nothing standing in between. That's why they can support 2 hanger levels. Perhaps if managed it well, it could be a damage survival feature to blow out the hanger rather than containing the induced explosion inside the ship. But it was not managed well in the Japanese ships.

One reason why the USN never pursued this path was US operating practice involved permanent deck storage of aircraft, and substantial flight preparation conducted on deck. British and Japanese practice involve 100% storage of air craft in the hanger and almost full light preparation in the hanger, with flight deck completely devoted to actual flight operation. This is why US carriers didn't need so much hanger space as pre-war Japanese and British carriers.

But even with the light construction, double storied hangers still had serious head clearance restrictions, and I believe Japanese carriers can not stow their own late-war carrier aircraft in at least one of their two hanger stories because of head room restrictions.

[Werner]

I don't think the thickness of Japanese or British hanger sides represents practice as much as other factors.

The US practice was to allow run-up of engines and fuelling of aircraft on hanger deck furing maintenance and prior to launch. In addition, the side exits were considered a valuable damage control asset, since armed aircraft or bomb pallets could simply be jettisoned over the side. They also experimented with aircraft catapults on the hangers and the retrieval of seaplanes through the side doors. The development of underway replenishment also caused a proliferation of roll-up doors and similar structures.

The British argued for protected hanger sides as a protection from severe weather as welll as fragments caused by near misses, with the expectation that British carriers would operate near enemy land bases.

Japanese carriers have no such requirement. Pacific weather is not usually as severe, and carrier operations near land bases were not considered likely. The hagar sides were therefore not protective in nature. They were probably mostly for light control. Unarmored flight decks coupled with a lack of bomb and aircraft disposal doors aboard Japanese carriers doomed them 65 years ago this month.

Lexington & Saratoga had a small lower space connected by the forward hanger. Usually, crated engines and aircraft parts were kept there.

[Dan K]

Actually, IJN carrier sidewalls for Shokaku class, and possibly earlier Soryu/Hiryu, WERE designed to blow out in case of explosion/overpressure. IIRC, per Kojinsha #6, sidewall thickness was 20 or 25mm.

Unfortunately, the design was hampered in part by a) the sidewall thickness itself and b), the Japanese tendency to install workrooms and storage spaces between the outer hangar wall and the hangar itself, effectively blocking up avenues for overpressure to escape, with bad results for rearranging the interiors.

[Werner]

I would have thought published data regarding Nelson's arrangements and possibly the Italian tests would have convinced them otherwise in plenty of time.

My frank opinion is the consideration of damage and control was strictly secondary in nature. Why would all the carriers at Midway have one ring fire system with piping composed of ordinary cast iron (like in your house's waste system) if any engineer had considered the effects of an explosion?

[Tim Stoneman]

Many Royal Navy carriers had two hangars to maximise aircraft capacity, given that the prewar doctrine was to stow all aircraft below deck, with no deck-park, in the event of likely air attack. The three battlecruiser ('large light cruiser' conversions - FURIOUS, COURAGEOUS and GLORIOUS) and ARK ROYAL (iii) had two full-length hangars. The first three Illustrious class ships had one, because of the extra topweight of the armoured hangar. INDOMITABLE was modified to have an extra lower hanger, half the length of the upper one, and so had a shallower upper hangar and thinner hangar armour. IMPLACABLE and INDEFATIGABLE were redesigned with two full-length hangars, but the additional complement for an extra engineroom, larger air group and more light AA meant they had the for'd part of the lower hangar given over to accommodation, workshops etc. The Audacious class (EAGLE (ex-AUDACIOUS) and ARK ROYAL (iv)) were built with two full-length hangars, but again the need for accommodation, workshops etc meant that, later in life, they too had the lower hangar shortened. Light fleet carriers (Colossus, Majestic and Centaur classes) had only one hangar; the abortive Malta and CVA-01 classes would also have had only one hangar.

[Guest]

I would have thought published data regarding Nelson's arrangements and possibly the Italian tests would have convinced them otherwise in plenty of time.

My frank opinion is the consideration of damage and control was strictly secondary in nature. Why would all the carriers at Midway have one ring fire system with piping composed of ordinary cast iron (like in your house's waste system) if any engineer had considered the effects of an explosion?

Japanese damage control may not have been secondary in consideration, but was certainly not well developed in doctrine.

Many examples suggests this:

1. Yamato's counterflooding space relies on natural flooding, the ship's fire main does actually have a discharge point into these counterflood space, thus if the ship lists seriously, the counterflooding space on the side high out of water, where counterflood would do the most good could no longer be counterflooded.

2. Japanese water tight doors in general requires the sailor to operate each dog individually. Thus in an emergency, with flood water chasing after them, the sailors could not possibly dog down the water tight doors fast enough.

3. Japanese water tight doors are pierced with escape man hatch to allow people trapped in enclosed spaces to escape. Touching gesture, but one might as well not have a water tight door in that case.

4. Japanese battleships seems to rely too much on heavy high capacity fixed pumps for flood water removal, and there are too few man portable water pumps, and there are too few hatches big enough for such man portable pumps to be easily menuvered through the ship.

In General, Japanese ships of WWII were well provided with natural flood restrictions such as bulkheads and native water tight integrety, but were partially defeated by poor detail design and inadaquately thought out damage control procedures.

[Vlad]

thanks for the contributions, I didn't realize so many carriers had two decks!

didn't the RN discover to their cost that one of their ships hangars was too shallow to fit the Corsair?

[Jack Ray]

Vlad asked:

didn't the RN discover to their cost that one of their ships hangars was too shallow to fit the Corsair?

Yes. The Indomitable and especially the Implacable class could not stow folded Corsairs. They were kept on a permanent deck park.

Because of the high demand for Hellcats in the USN, not many were provided to the RN, so they got Corsairs. The Grumman planes (Wildcat, Avenger and Hellcat) were much better suited to the low-headroom hangars.

Jack

[Tracy White]

RN Corsairs actually had their wing tips re-shaped to a squared off end just to allow them the extra inches necessary to fit into the Royal Navy carriers.

[bgire]

The French never-were carriers Joffre and Painlev� where designed with double level hangars, the lower one being aimed at repair and spares place.

Both hangars were structural with the hull. Lower hangar was connected to the upper one with a single internal elevator, as shown on this section (from 1938 original plans)



The elevator is in the red rectangle

[Guest]

The French never-were carriers Joffre and Painlev� where designed with double level hangars, the lower one being aimed at repair and spares place.

Both hangars were structural with the hull. Lower hangar was connected to the upper one with a single internal elevator, as shown on this section (from 1938 original plans)



The elevator is in the red rectangle

Are there any good drawings of these ships?

[Werner]

They were top secrets in a country known for xenophobia. I'd be glad with what is available now, and what is found in attics as tine moves on.

[middle_watch]

2. Japanese water tight doors in general requires the sailor to operate each dog individually. Thus in an emergency, with flood water chasing after them, the sailors could not possibly dog down the water tight doors fast enough.

Interesting argument, but I don't think I agree, you might be surprised just how fast you can dog down a door or hatch with the sea or fire coming at you (or in one case I recall vividly, the Chief Stoker after you just dropped something heavy on his foot)! We were trained to get the two clips opposite the hinges on first then you used knees, feet, elbows and hands to slam the rest in place and finish off with a hearty crank of a samson bar on the lot. An experienced hand made the operation sound like a machine gun firing a short burst.

The Batch 3 Type 22's I later served on had wheel locks on the main drag doors but they were prone to wear and damage even under general use and after continued usage failed to give good gas seals, in action I imagine the warping effect of explosions would make them unusable a lot sooner than a clipped door. It was also difficult to give the door a good old shoulder charge against pressure and lock the wheel shut at the same time.

[bgire]

Are there any good drawings of these ships?

Official original plans "as -to be - built" should be available for free download from the SHD website by early July. Watch this space :

http://www.servicehistorique.sga.defens ... tebato.php

They were top secrets in a country known for xenophobia. I'd be glad with what is available now, and what is found in attics as tine moves on.

For your information :
Official plans for Joffre had been considered lost for 55 years. They were seized by the invading German in Brest shipyard in 1940 and sent to Berlin for study by the Nazi "BuShip". in 1945, they were again seized by the Soviets and taken to Moscow for study. They were brought back to East Germany sometimes during the Cold War.
After the Fall of the Berlin Wall, the lost plans (and many others : about 175 linear metres of archives) were found in Potsdam. The German naval attach� offered them to France in 1992. Upon arrival in Paris, they were studied and declassified by the Service Historique naval staff and ended in the CAA military archives centre.
Some of the plans are heavily damaged and most of them still bear both German and Russian pencil writings (translations of the French data).
These plans will soon be available for free download worldwide (next month, AFAIK)

... nothing related with secret or xenophobia, just History