1940 Royal Navy Anti Battleship bomb

yulzari

Staff Sergeant
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The Fairey Albacore could carry 2,000lb of bombs and was to be the strike arm of the Fleet.

What if, years before, they decided that the easiest way to deliver a 15” shell and hit a moving battleship at extreme ranges beyond gun technology was to dive bomb it from an aeroplane.

So what would it take to achieve this?
 

EwenS

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From The Pacific War Online Encyclopedia

“The Japanese apparently did not develop an armor-piercing bomb until 1941. The Type 99 Number 80 Mark 5, used at Pearl Harbor, was remanufactured from obsolete 16" battleship shells. Out of a total weight of 800 kg (1760 lbs), the bomb had a charge of just 23 kg (50 pounds) of Type 91 explosive. The Type 99 had two base fuzes with 0.2 second delay that were insensitive enough to require impact on armor plate for fuze initiation. One such bomb went clear through Vestal at Pearl Harbor to explode on the harbor floor under the ship. The Type 99 was judged capable of penetrating 5.75" (146mm) of deck armor when dropped from a height of 10,000 feet (3000m). Unfortunately for the Japanese, the Type 99 had a high dud rate, due to weaknesses in the bomb case introduced during the remanufacturing process and poor quality control with the explosive fill. Of those that scored hits at Pearl Harbor, 20% failed to explode and another 40% yielded only low order explosions. The Japanese never developed an armor-piercing bomb light enough to be carried by a dive bomber, probably because they did not believe it was possible to develop a lighter AP bomb capable of penetrating battleship deck armor, and possibly also because of the shortage of the high-quality steel required for such weapons.”

If the shells were obsolete, I doubt there would have been any”turf war”.

Edit - see page 35 (page 36 of the .pdf file) of this official 1945 US report on Japanese bombs

Edit 2 These bombs were dropped by Nakajima B5N2 torpedo bombers from level flight. They were not a dive bomber weapon as the Aichi D3A Val was limited to a 250kg bomb load under the fuselage.
 
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EwenS

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You may be interested in Chapter IX (p161) and Appendix VIII of this document.

Note it gives Feb 1942 as the date of service entry for the British 2,000lb AP bomb despite it being in development since the 1920s.

For novelty there is the B, or Buoyancy Bomb.

There was a similar weapon developed in WW2, the Johnny Walker bomb whose only use IIRC was in Operation Paravane against the Tirpitz in Sept 1944.

Johnny Walker

nhygnghyf.jpg


This was a 400lb weapon.
 

EwenS

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Or Barnes Wallis could do his stuff a bit sooner and you could have Highball, the 500lb version of the Upkeep Bouncing Bomb used by 617 squadron to breach the Dams.

Two carried in tandem in the belly of a Mosquito. 618 squadron formed to use them. Postwar there were trials with a created version to fit in an Avenger bomb bay.
 

Shortround6

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What if, years before, they decided that the easiest way to deliver a 15” shell and hit a moving battleship at extreme ranges beyond gun technology was to dive bomb it from an aeroplane
It is the wrong question.
The 15in shell (AP) and the Japanese 16in shell were designed to go through the side armor at an angle of around 10-30 degrees.

The deck armor is much thinner than the side armor. On the other hand, unless you drop from around 5,000-10,000ft your bomb won't gain enough speed to punch through.

Aircraft bombs can be made longer and skinner than Battleship shells and can concentrate the weight into a smaller area.

The British 2000lbs AP bomb (actual weight 1934lbs) was 13.5in diameter. The old 13.5in shells weighed about 1250lbs so we can see that the 2000lb AP is a better bet.
However the 2000AP bomb may have been a bit too much of a good thing. Several times it went out the bottom of anything less than the Tirpitz and often didn't explode then.

But on the other hand (again) the AP bombs need the same sort of alloy steel, the same forging techniques and the same/similar heat treatment as major caliber AP shells and compete for manufacturing "space".

The Japanese did bore out the body of the shell to create a bit more space for the explosive.
 

Thumpalumpacus

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Isn't that essentially what the Japanese did?

In part. They modified 16" shells from the Nagato class iirc, but hung them on B5Ns and were dropped from altitude using a level attack profile.

Sticking these heavy shells on dive-bombers may or may not have been possible, I don't know that much about the technical issues, but I highly doubt they would pick up the speed to match the speed of plunging fire shot from the warships, and armor penetration would likely suffer as a result.
 

elbmc1969

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Feb 16, 2019
I don't know that much about the technical issues, but I highly doubt they would pick up the speed to match the speed of plunging fire shot from the warships, and armor penetration would likely suffer as a result.
I have looked at this--the bombs would be considerably slower than shells. However, the shells won't plunge at more than a 45 degree angle, and usually much less. By contrast, the bombs hit at close enough to 90 degrees that it doesn't matter.

In addition to the effective thickness of the armor, there's really no chance of a ricochet, deflection, or anything else, which simplifies matters.
 

EwenS

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Here is some more data on the Japanese 800kg bomb from the Navweaps site:-







WNJAP_161-45_3ns_bomb_pic.jpg
Type 99 No 80 Mark 5 Bomb. Digital image by Andy Hall based upon a drawing by John F. De Virgilio. The grid in the background is in one-foot squares (0.09 m2​). Digital image copyrighted by the PAST Foundation and the Submerged Resources Center of the National Park Service and used here by their permission.


Aircraft Bombs





CharacteristicType 99 (Model 1939) No 80 Mark 5Type 2 (Model 1942) No 80 Mark 5 Model 1
Total Weight1,757 lbs. (796.8 kg)1,788 lbs. (811.2 kg)
Bursting Charge49.4 lbs. (22.4 kg) TNA78.7 lbs. (35.7 kg) TNA
Length oa92.6 in (235.1 cm)91.7 in (233.0 cm)
Diameter16.1 in (40.9 cm)15.9 in (40.4 cm)
Nose thickness19.17 in (48.7 cm)11.97 in (30.4 cm)

  • These bombs were designed to penetrate the deck armor of the new USA Battleships of the 1930s-40s. From performance testing in January 1941, the bomb was considered to be able to penetrate 150 mm deck armor (5.9") from a dropping height of 8,200 feet (2,500 m) and an average striking speed of 738 fps (225 mps). At the time of the test, Japanese Industry lacked the technology to produce a deck armor plate with a performance close to that of USA plates, so 150 mm plates were imported from Germany and these were used to create an 82 ft2​ (25 m2​) target plate. Data from "Brief History of the Naval Air Squadron."
  • An aluminum plug was used between the burster and the cap as a shock absorber.
  • Both bomb types had two base fuzes to ensure detonation. However, these fuzes do not appear to have been reliable. During the Pearl Harbor attack, although one of these bombs is thought to have destroyed USS Arizona (BB-39), at least three did not explode. USS Tennessee (BB-43) was struck by two bombs, the first exploding on the center gun of Turret II and the second striking the top of Turret III but did not explode. Two dud bombs struck USS West Virginia (BB-48), the first of which hit the top of Turret III and broke up while the second went through the foretop and penetrated down to the second deck at frame 70. It was recovered nearly intact during salvage operations in May 1942.

WNJAP_161-45_3ns_Type-99_sketch_pic.jpg
Sketch of Type 99 Bomb from "Hawaii Operation."

And here is a photo showing (on the left) the shell it was manufactured from. In the remanufacturing process some 200+kg of material was removed to shape front & rear ends. Note the height when compared with the diagram at the top of this post. The shell on the left is minus its ballistic and AP caps. The shell on the right is the fully assembled article waiting to be fired. The shell in the middle is a 36cm shell.

1660633149131.png
 

EwenS

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Oct 19, 2021
It is the wrong question.
The 15in shell (AP) and the Japanese 16in shell were designed to go through the side armor at an angle of around 10-30 degrees.

The deck armor is much thinner than the side armor. On the other hand, unless you drop from around 5,000-10,000ft your bomb won't gain enough speed to punch through.
That statement is not entirely true.

As guns got bigger, the range increased and to exploit the power of these weapons the angle of firing increased so that shells were falling on an enemy deck, not punching through the side armour. And so the shells were redesigned to allow for that. Jutland probably represents the turning point in thinking.

The 16" turrets in the Nagato class, for which the shells converted to aircraft bombs were designed, had an elevation of -2 to +35 degrees. At 25.5 degrees the range was 32,810 yards (30,000m) at which point the shell was striking at a speed of 1,516 feet per second and at an angle of 34 degrees (no figures available for 35 degree elevation). In the mid-1930s the Nagatos had their turrets replaced. The new turrets were capable of 43 degree elevation. While no data is available for these I would expect the shell to be falling at an even steeper angle.

As you will see from the previous post the basic Japanese AP shell was a fairly blunt object. It was given an AP and then a ballistic cap to produce the final shell.

In Britain, gun elevations increased over time. Most of the 15" gunned battleships were built with turrets capable of 20 degree elevation. At that elevation the gun had a range of 23,734 yards. At that range the WW1 AP shells were falling at an angle of 29 degrees. But the turrets in Hood had an elevation of 30 degrees, which pushed the range out to 29,000 yards by which time the shell was striking at a speed of 1,326fps at an angle of 42 degrees. Prior to WW2 Queen Elizabeth, Warspite, Valiant and Renown all had their turret elevations increased to 30 degrees. New longer shells were introduced as well, which pushed the range out to 32,500 yards by which time the shell was striking at 1,446fps at an angle of 40.7 degrees.

This diagram shows the differences between British AP and HE 15" shells from WW2

1660635637089.png


The USA went from 15 degree elevation to 30 degree elevation with the Tennessee class in 1916/17.
 

elbmc1969

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Feb 16, 2019
And here is a photo showing (on the left) the shell it was manufactured from. In the remanufacturing process some 200+kg of material was removed to shape front & rear ends. Note the height when compared with the diagram at the top of this post. The shell on the left is minus its ballistic and AP caps. The shell on the right is the fully assembled article waiting to be fired. The shell in the middle is a 36cm shell.
The men in this photo are significantly shorter than the 6 foot tall nominal person in the photograph. Based on Japanese heights at the time, they're likely around 5.5 feet tall, maybe a little less.

(Diet caused Japanese to be relatively short--lack of calcium mostly, but a lot of Japanese ate fairly low-protein diets.)
 

Shortround6

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The big change in thinking was the Americans when they went for the heavy shells, they sacrificed side armor penetration for deck armor penetration at long range.

But that only applied to the modern 16 in guns and 6/8 in cruiser guns and the 12 in guns of the Alaska class so it was a minority.


The Japanese and British shells were more product of their times. There wasn't a big change in the design of the shells from the early 13.5/14in guns and the 15/16in guns of WW I.
Yes they changed the elevation of the guns but they didn't change the design of the shells.

The British were one of the few nations that introduced more streamlined shells for the older guns. But partly to get more range without having to rebuild the gun mounts/turrets to change the elevation.

This is getting away from my point, which is that, especially in the 1930s and very early 40s, it sounded like a simple solution just to grab battleship shells and modify them but the carrier aircraft available weren't suitable to carry 1500-2000lb bombs. The engines weren't powerful enough.
And the number of ships that needed to be hit by 1500-2000lb AP bombs was rather small.
Even later in the war (after 1942) the US carriers only allotted space for 20 1600lb AP bombs in magazines.


Air staffs often place orders for weapons to meet future needs.
The British spent quite a bit of time in the 1920s on a 1500lb AP bomb but their goal was to penetrate in of armor from 10,000ft.

The tests were conducted by firing projectiles from guns at target plates. Using guns to test bombs was pretty standard as they could adjust the powder charge to give them the impact veleocity they wanted and testing was a lot simpler than dropping bombs from altitude. But 7in was too stiff a requirement although 6in was doable.
Using impacts of a bit over 800fmp and 10-20 degree impacts they could get through 6in.

The did a few tests at lower velocities against 3 in armor, it was judged that in 1928 the only ships afloat that could have stood up to the 1500lb were the Nelson and Rodney.
However what is not said is how many hits would it take. A hit the magazine should be a kill, a hit in the boiler room may be a mobility kill. a hit in the bow ahead of the magazines may be several month repair job.

A lot of countries were rather optimistic in their bomb aiming capabilities.
Part of which goes back to intentions and planning.

The Japanese got a few hits on the American BB at Pearl Harbor and the converted BB shell did it's job.
However, how many did they drop?
None of the ships were moving.
AA fire was somewhat haphazard.
Battleship row was 4 ships long just about touching and 2 ships wide with 2 spaces empty (making one column of 4 and one of two, with the repair ship USS Vestal taking up one of the BB berths. Vestal may have been hit by an AP bomb (?). In any case Battleship row was a substantial target size wise.

If you are going to drop from high enough to go through a lot of armor the accuracy is not going to be good.
If you drop from low altitude you are not going to go through thick armor anyway.
 

elbmc1969

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Feb 16, 2019
Good book, very informative.
It's essential because there are no other deep sources available. However, it's flawed, with some serious editing errors and some leaps in logic that push through the authors assumptions instead of what's documented. There's also some material that just isn't clear, and some that's contradictory.

Overall, though, required reading for everyone interested in the Fleet Air Arm.
 

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