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"Armoured versus unarmoured" Topic


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Personal logo ochoin Supporting Member of TMP12 Feb 2020 2:39 p.m. PST

I was watching a rather good video on Youtube about IJN Taiho.

It touched upon the change made to the usual Japanese practice of having unarmoured flight decks (like the Americans) to armoured (including belt armour), like the British practice.

Is there any consensus which is better?

Personal logo Herkybird Supporting Member of TMP12 Feb 2020 3:07 p.m. PST

I think an armoured flight deck was better against kamikazes and was less vulnerable to an aviation fuel fire on the deck.
On the minus side, it probably was harder to repair minor damage.

rmaker12 Feb 2020 3:35 p.m. PST

It also made the ship more top-heavy and, in the British ships at least, brought the flight deck closer to the waterline. In RN practice the flight deck was the strength deck, while in USN usage, that would be the hangar deck, with the flight deck being superstructure.

And there were damage control trade-offs as well. Since the USN hanger was on the strength deck, damage above that might put the ship out of action, while damage in the hangar on a British carrier could well sink the ship, or at least damage it beyond repair. No British carrier could have survived the pounding that the USS Franklin took.

Personal logo ochoin Supporting Member of TMP12 Feb 2020 8:16 p.m. PST

The fact that modern carriers have armoured flight decks is because of the fundamentally different type of aircraft than those used in WW2?

From my (limited) reading, it was the heroism of damage control parties (& some luck) that saved the Franklin & the Bunker Hill.

hindsTMP Supporting Member of TMP12 Feb 2020 8:22 p.m. PST

With all due respect, rmaker, you are making questionable statements here.

A properly designed ship would not be "top heavy" regardless of whether or not it had an armored flight deck.

WRT your claim that "No British carrier could have survived the pounding that the USS Franklin took.", in the 3/19/1945 incident, Franklin was hit during a low-level bombing run by two 550 pound SAP bombs, which penetrated the flight deck, causing secondary explosions on fueled and armed aricraft. These bombs likely wouldn't have penetrated the armored flight deck of a British Illustrious class CV, which was designed to resist 500 pound bombs dropped from altitude. The bombs which damaged Illustrious in the Med were in the 1000 and 2000 pound range, dropped from dive bombers.

Dn Jackson12 Feb 2020 10:24 p.m. PST

I always understood that the armored flight deck limited the number of planes a British carrier could hold since it wasn't just the deck that was armored. It was an armored box with a ship built around it.

Martin Rapier12 Feb 2020 10:56 p.m. PST

It isn't a question of better, just appropriate. British carriers were designed with one eye on operating in the congested waters of the North Sea and Mediterranean , within range of more land based air than you could share a stick at.

Big Red Supporting Member of TMP13 Feb 2020 6:11 a.m. PST

One American admiral commented about carrier damage from kamikaze attacks off of Japan: a kamikaze attack on a US carrier was six months repair at Pearl Harbor, on a British carrier it was up sweepers.

Minor damage to a British carrier flight deck was often repaired with quick set concrete – permitting air operations to quickly resume.

4th Cuirassier14 Feb 2020 2:41 a.m. PST

When the armoured carriers were designed in the 1930s radar was not thought of, so there was no way of being sure its fighters would be able to find and intercept incoming strikes. Even if they could, the compromises required for carrier operability meant that carrier fighter performance could not be expected to match that of land-based air.

So the thinking was that you should expect to get hit, and so your carriers should be able to survive getting hit. The flight deck was the strength deck and it was treated like a magazine.

It all made sense in 1935. By 1940, less so.

Illustrious duly took six hits to the flight deck from Stuka bombs of 500 and 1,000kg weight. There's no instance of any other carrier taking that and surviving. Akagi was twice the size and was destroyed by one 1,000lb bomb.

On the other hand, there is an argument that the carriers only got hit on their armoured deck in the first place because of that armoured deck. All that weight high up raised the metacentric height and so it had to be set as low as possible. This in turn reduced the size of the hangar and the number of aircraft it could carry, including fighters. If the air group had been bigger, goes the argument, the bombers would never have got past the fighters, the bombs would never have hit it in the first place, and so you didn't need an armoured deck at all. Ergo, you want an unarmoured flight deck and a 70-plane air group that's 2/3rds fighters. 1/3 go off to bomb escorted by half the fighters, while the other half defend the carriers.

This design worked brilliantly in the 1944 carrier battles, but ironically the British approach worked better in 1945 when the Japanese did the unexpected with their kamikazes. These bombers did get through, by overwhelming the defences with 100+ one-plane raids, and did huge damage to unarmoured carriers. It is a myth that they did no damage to the armoured carriers though. Although they survived kamikazes better, at least one was permanently slightly bent thereafter.

Taiho's story is very typical in a way. Japanese carriers were kind of cargo cult designs. They looked like carriers, but as though built by people who'd read descriptions of them, but had never seen one. So they had flat tops and air groups, but they often had the islands on the wrong side or no island at all. Some had motorbike exhausts along the edge of the flight deck or outward leaning funnels to vent the smoke. They had AA but most of it was so short-ranged it could only hit targets already diving on them. None had proper damage control. In a US carrier, everyone had a job and a damage control station. In a Japanese carrier, there was a damage control department, unless they got included in the damage in the first place, in which case there wasn't. Who needed damage control on a Japanese carrier anyway? It would always be the IJNAF doing the bombing.

Taiho was likewise an armoured carrier but not a proper one, because the hangar wasn't treated as a magazine. She was lost because a torpedo hit and fractured the avgas storage tanks, and someone switched on the aircon to get rid of the smell. The fumes distributed through the ship inevitably found a naked flame and blew her up.

The optimal solution of course is to make the carrier twice the size, so it can have deck armour, and a big air group, and enough deck-edge real estate to establish some really, really lavish organic AAA, as per the Midway-class CVBs of 1945.

Personal logo ochoin Supporting Member of TMP14 Feb 2020 3:04 a.m. PST

There was something about the elevators on the Taiho being very deep: below the waterline, in fact.

The av gas fumes collected in there & were spread through the ship. It wasn't "to get rid of the smell" that the mistake was made. You're underestimating the Japanese. Admittedly, it was a bungle by damage control but they were trying to rid the ship of volatile fumes. What happened was what they feared.

hindsTMP Supporting Member of TMP14 Feb 2020 10:30 a.m. PST

It is a myth that they did no damage to the armoured carriers though. Although they survived kamikazes better, at least one was permanently slightly bent thereafter.

SFAIK, only "permanent" in the sense that it was decided to keep them (most notably HMS Illustrious) in service with inadequate repairs, rather than to send them to a dockyard for complete repairs a common occurrence in wartime. In the case of HMS Illustrious, the ship was already damaged prior to the last kamikaze attack, including the hull and shafting.

Here's something from the Internet (not requiring a book purchase): link

Murvihill16 Feb 2020 4:34 a.m. PST

Compare two equivalent Carriers: The HMS Illustrious was 23000 tons, commissioned 1940, top speed 30 kts. She initially carried 36 aircraft, rising to 53 at the end of the war. The USS Hornet was 20000 tons, commissioned 1941, top speed 32.5 kts. She carried 90 aircraft. I'd say the trade-offs for the armored flight deck were pretty steep.

4th Cuirassier16 Feb 2020 2:43 p.m. PST

Yep that's why Illustrious was sunk and Hornet wasn't.

CaptainCorcoran17 Feb 2020 5:54 a.m. PST

4th Cuirassier gives a very good summary of the armoured carrier concept. For a detailed analysis of the design and operation of armoured aircraft carriers in WW2 I thoroughly recommend this website: armouredcarriers.com

There is a huge amount of information and detailed historical reports etc. on this website. Some very good operational details and damage reports as well as discussions on armoured v unarmoured.

The pounding Illustrious took off Malta and survived is testament to the construction of these ships and also the excellent damage control. She took 2 hits from 500lb bombs (250kg); 2 hits from 1100lb (500kg) bombs; 2 more hits from either 500lb or 1100lb bombs; and a hit from a 2200lb (1000kg) bomb as well as three near misses. Read about the damage and the efforts taken to save the ship here: link

It would take 9 months to repair the damage and the ship had problems with her propeller shaft for the end of her life. By 1945 ships like Illustrious were worn-out by 5 years of conflict just like Enterprise but both ships continued to provide good service. Illustrious was withdrawn from operations in the Pacific in April 1945 following a very near miss from a 2200lb bomb exploding under water.

Given the design restrictions the first class of armoured carrier (Illustrious, Formidable, Indomitable & Victorious) were originally designed to carry 36 aircraft, this later increased to a maximum of 57 aircraft using deck parks. The two Implacable class armoured carriers could carry 81 aircraft.

The Yorktown class of US aircraft carriers were designed to carry 90 aircraft but that included aircraft broken down in crates. For example USS Yorktown operated 53 aircraft at the Battle of Coral Sea (with 13 spares) and at Midway would operate 75 aircraft. None of this class were able to operate 90 aircraft – only the much larger Essex class could do that.

Murvihill19 Feb 2020 7:06 p.m. PST

Still, half the planes on a hull is a big sacrifice. What if the air strike on Taranto were made with twice the planes?

4th Cuirassier20 Feb 2020 2:39 a.m. PST

What if it were made by none because each carrier had previously been taken out by one bomb? That was the concern the armoured carriers were built against.

The US carriers faced the opponent they expected, usually with numbers on their side, and four were sunk. The RN carriers also faced the opponent they expected and they all survived. So the design was pretty effective, I would suggest, although definitely not future proof to fundamental changes in aircraft type.

hindsTMP Supporting Member of TMP20 Feb 2020 12:46 p.m. PST

@Murvihill

The air strike on Taranto was only 21 planes, not because the Illustrious couldn't carry more, but because the RN didn't have them. If you look at air group numbers prior to the RN getting large numbers of lend-lease aircraft, carriers almost always carried less than their designed air groups. I guess the RAF had priority for available production, including Bomber Command of questionable cost-effectiveness.

Murvihill20 Feb 2020 7:59 p.m. PST

Hornet was not taken out by one bomb. It was taken out by three bombs, one kamikaze, 16 torpedoes and 400 5" shells.

4th Cuirassier21 Feb 2020 3:47 a.m. PST

Nobody said Hornet was taken out by one bomb, but it was entirely possible for this to befall an unarmoured carrier. I can think of two examples offhand, namely Akagi at Midway and Princeton at Leyte Gulf.

Murvihill22 Feb 2020 6:01 a.m. PST

The Ark Royal was taken out by one torpedo, does that make the British aircraft carrier more susceptible to torpedo damage than the American fleet? Your position appears to be that a more defensible ship is more important than more airplanes and mine is that as an offensive weapon more airplanes is more important. I don't think we're going to come to an agreement.

4th Cuirassier22 Feb 2020 1:47 p.m. PST

My point is simply that there were solid reasons to accept a smaller air group, so – in response to the OP's question – it is difficult to conclude that either was better.

Ark Royal was unarmoured, so was closer to the US design, for the same reason: to maximise offensive power. It clearly carried risks.

The offensive ability of Ark Royal, Lexington, Yorktown, Hornet and Wasp was significantly eroded by being sunk.

The optimal design was clearly both an armoured deck and a large air group, which is why the USN's Midway and the RN's (cancelled) Malta class.

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