Did RN Illustrious Class armoured decks provide significant benefit against bombs?

[RCAFson]

Parsifal, any thoughts on the armour vs wood for the #2 bomb impact?
I wonder if the 3" deck armour helped slow the bomb (although too thin to stop a 1,000 lb AP bomb) might have slowed it down a bit, enough to make it explode above the waterline? (instead of below)

The deck was only armoured above the hanger, so the flight deck forward and aft of the elevators was only thinly protected, probably by an inch or so of 'D' steel as armour, rather than the 3in armour over the hangers. It is possible that the bomb's fuse was initiated when it passed through the deck and this prevented it from detonating in the water. One 500kg (or maybe 1000kg? - hit # 4 below) bomb did pass through the armoured deck over the hanger, but with almost no remaining velocity and it actually detonated above the armoured hanger deck, The combination of an armoured flight deck and an armoured hanger deck, made it almost impossible for any WW2 era bomb that could be carried by an axis attack aircraft to penetrate into her machinery spaces. This website also suggests that Illustrious also suffered the equivalent to a kamikaze strike during the initial Jan 1941 attack:

1. Hit and destroyed the starboard S2 pom-pom, killing most of the crew;
2. Penetrated the forward end of the flight deck and passed overboard, exploding above the water. Caused extensive splinter damage to several compartments and started a fire in one;
3. Exploded in the after lift-well, 10-20 ft below the flight deck, severely damaging the lift and destroying a Fulmar on the lift;
4. Penetrated the armored flight deck and exploded just above the hangar deck, damaging the forward lift and surrounding structure, and starting a fire on the hangar deck. Several aircraft in the hangar deck were destroyed;
5. Hit the after end of the after lift, adding to the damage of bomb #3;
6. Penetrated a pom-pom platform, passed through the shipand went overboard without detonating. A fire was started on two mess decks.
7. Also hit the after lift, completing its destruction.
8. A near-miss off the starboard side caused slight structural damage and minor flooding.

It could have been worse; although caught out of position during the initial attack, her fighters were able to disrupt the latter half of the attackers, and were credited with five victims between them. To add to the bomb damage, one of the shot-down Ju87s also crashed onto the deck near the after lift well, starting a fire and adding to the damage to the after end of the ship. Fires blazed out of control on the hangar deck and in other compartments, including near her for'ard magazine, and flames shot out of the aft lift well. Her rudder was out of action, as was her flight deck, forcing her remaining airborne fighters, low on fuel and ammo, to make for Malta. Steering by differential revolutions of her engines and listing, Illustrious laboriously followed them.

HMS ILLUSTRIOUS

Hit # 4 would probably have crippled a Yorktown class carrier and maybe even an Essex as the bomb would have passed through the armoured hanger deck and then exploded in the machinery spaces.

 

[RCAFson]

I think all three of the big Navies had armouring schemes for their big carriers. For the Yorktowns, the Illustrious and the Shokakus they were all protected by an armoured deck, moreover the weight of the armour scheme was overall very similar for all these ships.

What set the british ship apart was that whereas the main armour deck in the USN and IJN was low down, below the hangar, in the British carrier it was a box that surrounded the Hangar. Putting the armour deck to the side and above the hangar, raises the CG and affects stability, so the only option the British could adopt was to knock an entire deck of the ship and reduce the size of the hangar. The result was that even under the best of conditions the british carriers could only carry 45 aircraft, although in 1944 they adopted a deck park like the USN, which raised the CAG to 53.

Comparing the Japanese and USN ships is interesting. The USN ships were the more balanced, IMO because they distributed the protection to both anti torpedo and anti bomb protection, whereas the Japoanese tended to concentrate more on vertical protection, below the waterline.

Illustrious had two armoured deck with a total thickness of about 6in; this was far thicker than any USN carrier before the Midway class, but the RN carriers also had a much heavier AA battery than any other carrier before the Essex class. Enterprise had only single 1.5in armoured deck while even Essex had only 2.5in hanger deck and another 1.5in over the machinery spaces.

Illustrious hanger was 85% as large as Enterprise's. CAG size was not primarily due to differences in hanger size.

 

[renrich]

The Saratoga had 16-five inch AA guns and 96 forties and twentys anywhere there was space. That is more than the Illustrious class.

 

[RCAFson]

The Saratoga had 16-five inch AA guns and 96 forties and twentys anywhere there was space. That is more than the Illustrious class.

Saratoga didn't receive her 16 5in/38 guns until mid 1942 and the other AA guns were added incrementally throughout the war. The RN armoured carriers remained the most heavy armed carriers until the Essex class, despite the fact that the Lexington class displaced nearly 50,000 tons, full load:

World Aircraft Carriers List: US Fleet Carriers, Pre-WWII

 

[Glider]

The Saratoga had 16-five inch AA guns and 96 forties and twentys anywhere there was space. That is more than the Illustrious class.

That may well be the case but the RN ships guns were a good match for the USN vessels. Also I believe I am right when I say that the weapons you mention were only installed in the Spring of 1945.

One questions, does anyone know how many aircraft she carried? The numbers I have vary between 63 and 90.

 

[Freebird]

Hit # 4 would probably have crippled a Yorktown class carrier and maybe even an Essex as the bomb would have passed through the armoured hanger deck and then exploded in the machinery spaces.

Thanks for your explanations RCAF.

So if I understand correctly, the #4 hit was probably the most serious, and likely fused on passing through the first 3" (deck) armour an then exploded over the second 2" (hanger floor) armour.

Passing through the first 3" of armour may well have slowed the bomb down enough that it couldn't penetrate the hanger floor.

On an Essex, assuming that the bomb fused passing through the wooden deck, the hanger floor may also have contained the blast.

However, the Yorktowns lacked any deck or floor armour?
What was under the hanger floor?
So a 1,000 lb bomb passing through the flight deck would likely have passed right though the hanger and into the machinery?

 

[renrich]

Glider, the Saratoga carried 90 AC and the figures I gave on AA guns were indeed the final figures in 1945. The Saratoga got her 16- 5 inchers in 1942 and I think the Lexington did also, before she was sunk. The Saratoga with 16-5 inchers was more heavily armed than the Illustrious class with 16-4.5s. Before the 40s were installed the US carriers had multiple 1.1s.

The Saratoga class had top speeds of 33 knots while the Yorktown and Enterprise could make 34 knots, all superior to the Illustrious Class at 31 and 32. In carrier operations a couple of knots does not make a lot of difference as far as surface actions are concerned but it can make a lot of difference in certain circumstances because of WOD.

Incidently the Ranger had a flight deck with one inch of armor. The fact is that all the major US carriers sunk in the Pacific, the Lex.,Yorktown, Hornet and Wasp, sank primarily because they were hit by torpedoes. Armored flight decks would have made little difference and the topside weight of them may have been a negative. Fortunately for the RN, their carriers did not have to deal with IJN torpedoes. The USN carriers with at least two squadrons more AC capacity and their open hanger decks were much better suited for the PTO than the RN carriers.

 

[RCAFson]

Thanks for your explanations RCAF.

So if I understand correctly, the #4 hit was probably the most serious, and likely fused on passing through the first 3" (deck) armour an then exploded over the second 2" (hanger floor) armour.

Passing through the first 3" of armour may well have slowed the bomb down enough that it couldn't penetrate the hanger floor.

On an Essex, assuming that the bomb fused passing through the wooden deck, the hanger floor may also have contained the blast.

However, the Yorktowns lacked any deck or floor armour?
What was under the hanger floor?
So a 1,000 lb bomb passing through the flight deck would likely have passed right though the hanger and into the machinery?

It seems unlikely that the thin flight deck of an Essex would initiate the fuse on an 1100 or 2200lb AP bomb, nor slow it appreciably, and thus penetration of the armoured hanger deck seems likely. From other sources, Enterprise had a 1.5" armoured deck, probably at the hanger deck level and this armour was penetrated even by 550lb IJN bombs (probably SAP) and this resulted in Yorktown being crippled by a bomb hit and then sunk by torpedoes at Midway.

 

[RCAFson]

Glider, the Saratoga carried 90 AC and the figures I gave on AA guns were indeed the final figures in 1945. The Saratoga got her 16- 5 inchers in 1942 and I think the Lexington did also, before she was sunk. The Saratoga with 16-5 inchers was more heavily armed than the Illustrious class with 16-4.5s. Before the 40s were installed the US carriers had multiple 1.1s.

The Saratoga class had top speeds of 33 knots while the Yorktown and Enterprise could make 34 knots, all superior to the Illustrious Class at 31 and 32. In carrier operations a couple of knots does not make a lot of difference as far as surface actions are concerned but it can make a lot of difference in certain circumstances because of WOD.

Incidently the Ranger had a flight deck with one inch of armor. The fact is that all the major US carriers sunk in the Pacific, the Lex.,Yorktown, Hornet and Wasp, sank primarily because they were hit by torpedoes. Armored flight decks would have made little difference and the topside weight of them may have been a negative. Fortunately for the RN, their carriers did not have to deal with IJN torpedoes. The USN carriers with at least two squadrons more AC capacity and their open hanger decks were much better suited for the PTO than the RN carriers.

A typically RN AHD carrier in mid 1942 had 48 x 40mm pom-pom with radar ranged Mk IV gyro gun directors and at least a dozen 20mm, in addition to 16 x 4.5in and IMHO this trumps Saratoga's AA outfit in mid 1942. Lexington carried 16 x 5in/38, 24 x 1.1in and 30 x 20mm guns at the time of her lossaccording to this article:http://www.militaryfactory.com/ships/detail.asp?ship_id=USS-Lexington-CV2

The USN ships were somewhat slower in service than on trials, and the actual speed differential was probably less then it seemed. Enterprise must have emerged from her refit as a slower ship considering that she had a much wider beam due to the added anti-torpedo blisters. According to HyperWar: War Service Fuel Consumption of US Naval Surface Vessels [CV], Saratoga's maximum speed was 31.8 knots, while the Essex class averaged 31.9 knots.

Wikipedia says Ranger has one inch of armour over her steering gear, which seems more likely than an armoured flight deck. given her small displacement.

Actually, Yorktown was crippled by a bomb hit at Midway that probably penetrated the thin armoured deck and was then finished off by torpedoes after she lost almost all power. Lexington and Wasp were sunk after tearing themselves apart due to their extremely unsafe avgas system, although two 55olb bomb hits probably added to Lexington's loss. It is unclear to me that the bomb hits on Hornet would have crippled her, but one 550lb bomb probably penetrated her armoured deck and two other hits severely damaged her flight deck, but she was torpedoed almost at the same time. At Coral Sea "...Yorktown, at 11:27, was hit in the center of her flight deck by a single 250-kilogram (551 lb), semi-armor-piercing bomb which penetrated four decks before exploding, causing severe structural damage to an aviation storage room and killing or seriously wounding 66 men...", according to Wikipedia.

 

[Freebird]

One 500kg (or maybe 1000kg? - hit # 4 below) .

The bombs dropped on Illustrious were 1,000 pound (~500 kilo) correct?
I don't believe that 2,000 lb bombs (or 1,000 kilo) were used?
(or am I wrong?)

 

[RCAFson]

The bombs dropped on Illustrious were 1,000 pound (~500 kilo) correct?
I don't believe that 2,000 lb bombs (or 1,000 kilo) were used?
(or am I wrong?)

They were either 250kg, 500kg or 1000kg, but different sources state different weights.

 

[Freebird]

They were either 250kg, 500kg or 1000kg, but different sources state different weights.

That's confusing as heck.

Do you know of any other attacks on carriers using 1,000 kg (2200 lb) bombs?

 

[RCAFson]

That's confusing as heck.

Do you know of any other attacks on carriers using 1,000 kg (2200 lb) bombs?

I found this info on the web:

http://web.archive.org/web/20041027065605/www.dcfp.navy.mil/mc/museum/War_Damage/british.pdf

it is the USN's assessment of bomb damage to RN ships up to mid 1941, including Illustrious in Jan 1941. The RN estimated the bomb hits as being either 250kg or (mainly) 500kg while the USN estimated that most of the hits were from 1000kg bombs. OTOH, both the USN and RN estimated that Formidable was hit by 1000kg bombs, and the wikipedia article states the same and also states that the hits on Indomitable were from 500kg bombs.

 

[Glider]

Glider, the Saratoga carried 90 AC and the figures I gave on AA guns were indeed the final figures in 1945. The Saratoga got her 16- 5 inchers in 1942 and I think the Lexington did also, before she was sunk. The Saratoga with 16-5 inchers was more heavily armed than the Illustrious class with 16-4.5s. Before the 40s were installed the US carriers had multiple 1.1s.

The Saratoga class had top speeds of 33 knots while the Yorktown and Enterprise could make 34 knots, all superior to the Illustrious Class at 31 and 32. In carrier operations a couple of knots does not make a lot of difference as far as surface actions are concerned but it can make a lot of difference in certain circumstances because of WOD.

Incidently the Ranger had a flight deck with one inch of armor. The fact is that all the major US carriers sunk in the Pacific, the Lex.,Yorktown, Hornet and Wasp, sank primarily because they were hit by torpedoes. Armored flight decks would have made little difference and the topside weight of them may have been a negative. Fortunately for the RN, their carriers did not have to deal with IJN torpedoes. The USN carriers with at least two squadrons more AC capacity and their open hanger decks were much better suited for the PTO than the RN carriers.

Thanks for the information. Looking at the aircraft at the end of the war The Illustrious class really contained three different class of vessel, The Illustrious, Formidable and Implacable the main difference being the hangers. Illustrious had one hanger deck, Indomitable 1 1/2 hanger decks and Implacable two decks. As you would expect this impacted the number of aircraft carried.
By war end The Illustrious class operated at war end approx 50 aircraft 36 Corsairs and 16 Avengers (March 1945)
Indomitable 72 aircraft
Implacable 81 aircraft. 48 Spitfires, 21 Avengers and 12 Fireflies (March 1945)

72 is still a good number and 81 pretty close to any other carrier. The theory that all RN carriers carried fewer aircraft is clearly incorrect.

Its worth noting that the Indomitable had more hanger space than the Enterprise and the Implacable had even more space than the Indomitable. The difference is the use of the deck park. There is also a difference on how the aircraft capacity of the ship was defined. I used to know it but unfortunatly cannot remember but, it included an allowance for spares which were included in the USN capacity but not in the RN capacity.
As an example if you look at the escort carriers, the USN Bogue class were rated as 28 aircraft, while the RN Attacker class were rated at 18 aircraft, but they were exactly the same ship design on lend lease. The RN did make changes to the ships before they were acceptable to the RN, but the hanger space was the same.

As for the guns the 4.5in may not have been as good as the 5in but it was still a good gun and the RN vessels had 4 directors not 2 but then again the USN director was better so the difference is minimal. As for the LAA then the RN vessels were probably a match for the Saratoga before her final refit, but clearly not after it.

As for luck then the RN didn't face Japanese torpedo's true, but then again the USN didn't face Japanese bombers dropping 1,000 or 2,000lb bombs on them.

 

[RCAFson]

Looking at these OOB pages:
http://www.navweaps.com/index_oob/OOB_WWII_Pacific/index_OOB_WWII_Pacific.htm
it seems that Lexington and Saratoga carried about 70 aircraft each during 1942.

 

[Glider]

Looking at these OOB pages:
World War II Battles Of The Pacific
it seems that Lexington and Saratoga carried about 70 aircraft each during 1942.

A very interesting site. Looking at the 1945 OOB I was expecting more Corsairs to be on the US carriers. Hellcats outnumber them by about 4-5 to 1and seem to be only on the large Essex class carriers.
However on the smaller RN carriers they were almost all Corsairs and Seafires.

 

[renrich]

One problem the USN faced early in 1942 in the Pacific was a shortage of aircraft and pilots. Seems hard to believe but some fighting squadrons were equipped with mixed types because of these shortages. That would account for the carriers not having as large a air complement as possible. Not only was there a shortage of AC but because there were no survival kits available, the galley was raided for kitchen knives and meat cleavers.

The Japanese carriers were slow to cycle strike groups because their enclosed hangar decks did not allow them to start and warmup engines except on the fight decks. The US carriers with their open hangar decks did not suffer from this. I have read that the British carriers in the Pacific had personnel heat problems because the hangar decks were enclosed. Does anyone know if the British carrier could start and warmup engines in the hangars?

 

[Nikademus]

Japanese and British hangers were both 'closed' only one was armored, the other not so the UK engines would also have to warm up on deck. The theoretical speed edge offered by USN open hanger designs turned out to be theoretical only...at least in 42, due to chronic issues with conducting deck operations for multi-squadron elements. The Japanese consistantly got off their strike packages quicker despite having to "warm up" the planes on the flight deck.

On the subject of UK carriers, DK Brown made an interesting comment about the UK having never lost a major carrier to fire at sea as being one of the pros of the UK CV design concept. Unfortunately he does not elaborate.

 

[RCAFson]

From reading other forums, it appears that the RN used electrical oil heaters to minimize warmup time. It seems to me that having a hanger full of fuelled up aircraft with their engines running is not such a good idea, and certainly this came to a complete end after the jet age when wooden decks also ended. Also moving such aircraft about the deck would have been extremely hazardous, or so it seems. However, the RN must have been able to start-up engines in the hanger while doing routine engine maintenance.

I also found this website with a lot of interesting info. According to it, Saratoga didn't receive any quad 40mm guns until the end of 1942 (which makes sense because I don't think they were in production until mid 1942.):
CV2 Lexington aircraft carriers (1927) - United States Navy (United States of America)
http://www.navweaps.com/Weapons/WNUS_4cm-56_mk12.htm
also representative air complements are given and they average about 70, with a high of 88 in Aug 1942.

Finally, it is interesting to speculate on the IJN using RN armoured carriers at Midway...I suspect that they would have all survived.

 

[Freebird]

The fact is that all the major US carriers sunk in the Pacific, the Lex.,Yorktown, Hornet and Wasp, sank primarily because they were hit by torpedoes. Armored flight decks would have made little difference and the topside weight of them may have been a negative. Fortunately for the RN, their carriers did not have to deal with IJN torpedoes. The USN carriers with at least two squadrons more AC capacity and their open hanger decks were much better suited for the PTO than the RN carriers.

I would agree that each nation designed with the primary theater in mind, the British for the N. Atlantic and the USN for the Pacific. However, I believe that in each of the 3, Lex, Yorktown Hornet, bomb hits were a major factor.

The fuel vapor fire on the Lex was very likely the result of a bomb hit, not a torpedo.

IIRC Hornet survived the initial attack, but could not operate aircraft due to the 3 bomb hits and the 2 Vals crashing onto the deck. Had they been able to launch CAP fighters to prevent the torpedo attack while under tow, the ship may have been saved.

The Yorktown was dead in the water for an hour after the first bomb attacks, and her ability to refuel launch fighters was impaired prior to the second (fatal) wave.

While the RN didn't face IJN torpedoes, they did face the much superior German U-boats, which is how the Germans sank the British carriers Eagle, Courageous Ark Royal. (other than Glorious to gunfire)
I suspect that torpedo planes were given absolute first priority by the FAA, likely conceding that a few bomb hits would occur, but also likely wouldn't sink the ship.
Interesting to note, no defended British fleet carrier was ever lost to air attack.