Aerial Bombing Question

I once saw a reference to a 'bomb undershield' which I noted having no idea what it was or what purpose it served. Maybe this had something to do with forcing spring loaded doors?
Cheers
Steve

stona said:

I once saw a reference to a 'bomb undershield' which I noted having no idea what it was or what purpose it served. Maybe this had something to do with forcing spring loaded doors?
Cheers
Steve

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The Wellington Bomber

This link mentions undershields (page 9), Iread a while ago that there was a mesh placed beneath bombs in aircraft which was broken when dropped but I cant find it again, so it is aerodynamic until the bomb is dropped.

I seem to remember reading that spring loaded bomb doors ran in to problems (hardly surprising) as the bomb load or number of bombs increased then the size of the doors and strength of the springs increased. On release of bombs if any were hung up for a few seconds an individual bomb was not heavy enough to open the door. That means the pilot is flying with an armed loose bomb rattling on the bomb doors which a heavy bump on landing means it drops on the runway. This in addition to the obvious loss of accuracy, could you program in the door opening time to a Norden or other bomb sight?

You could probably program or put in the circuit for the doors to open, however, if they didn't open then the sequence would be interrupted and no bombs would drop (hopefully). I was under the impression that the doors were opened early to allow for manual opening should they malfunction. I would hate to fly that far, through that much hell to not drop.

Cheers,
Biff

BiffF15 said:

I was under the impression that the doors were opened early to allow for manual opening should they malfunction. I would hate to fly that far, through that much hell to not drop.

Cheers,
Biff

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That was certainly normal procedure for the RAF and I think it was for the USAAF too.

It would be unfortunate to fly all the way to the target, only to be unable to drop the bomb load, but a surprising number of loads were dropped 'safe' by crews of all air forces.This might seem incomprehensible, but I'm sitting with a recording of this morning's Grand Prix in the background with a cup of tea and couple of slices of Marmite toast, not freezing my arse off in a noisy bomber confronted by searchlights, flak and fighters.

Cheers

Steve

Most fuses have to fall quite a distance before they're armed. No armorer is going to put a quick arming fuse on a bomb on a bomb dropped at high altitude, it'd be a waste of a specialized fuse, and a needless danger to the crew.

Quick arming fuses were for low altitude missions, and usually smaller bombs too.

Not every fuse could be used with every bomb. Just because a fuse was quick arming didn't mean it was also quick exploding. A lot of quick arming fuses had delay built in, the delay was after the bomb struck, giving the aircraft time to get out of the immediate area before the bomb exploded.

The M112A1 tail fuse for example took about 80 to 100 air travel to arm, meant for low level use. It had defferent delays that could be installed, one 4 to 5 seconds delay, another 8 to 15 seconds delay. They could be used on up to 300 lb GP bombs, the similiar M113A1, and M114A1, could be used on the bigger 500lb GP and semi-AP bombs up to 2000lbs.

Some fuses delay could be adjusted on the nose cap, some had to be assembled with different delays before they were installed on the bombs.

There were a lot of fuses, and a lot of different missions profiles for them to fit. The one book I have on WW2 aircraft fuses ( USA only ) has over 30 different fuses, and that's not a complete list.

The two pistols/fuses I cited were in common use on British bombs. Both were armed once the vanes had spun a relatively few times. As soon as the bomb was released the arming wire would be pulled out and as soon as the bomb hit the air stream the vanes would start to spin. It doesn't take long or far for the vanes to spin the fairly few revolutions to arm the bomb.
This would render the majority of bombs dropped on a typical raid liable to detonation. At the beginning of the war Bomber Command dropped about 25% of high explosive bombs with long delay pistols or fuses, usually incorporating an anti-removal/anti-tamper device. This figure diminished as the war progressed and more and more targets were saturated with more powerful, instantaneously exploding bombs.

Take the No. 27 nose pistol already mentioned. This was commonly used for general bombardment.
As the bomb was loaded the closed end of the safety fork (which prevented the rotation of the arming vanes) was fitted with an arming wire, attached to the aircraft. The safety pin at the opposite end (open end) of the fork was now removed. When the bomb was released the safety fork was removed by the arming wire and retained on the bomb carrier. The arming vanes rapidly spun off ( I can count 12 rotations required on my diagram, but it could be a couple more or less, counting threads on a shaft is not easy!), exposing the pressure plate attached to the striker. This would happen with the bomb still close to the aircraft. Any significant blow to the pressure plate would force it and the striker inwards, breaking the shear wire and forcing the striker point on to the detonator percussion cap, thus initiating the detonation chain. Given that most bombs were fused for instantaneous detonation this means that the bomb would explode immediately, and not far from the aircraft.
Whether a bomb was ever likely to receive a suitable impact in the correct place to detonate is another question altogether. I have never read an account when this happened, but it was theoretically possible.
Even the simplest fuses had creep springs and shear wires fitted below or to the striker, ensuring that a solid impact was required to initiate detonation, a glancing blow would not do it.

The crucial point is the amount of time after the bomb left the aircraft for it to be armed. I don't think it took far or long for the vanes to unwind in a 200mph wind. Given that most British bombs used in general or area bombardment had zero delay (they were fused for instantaneous detonation) delay is completely irrelevant.

Some fuses were very complicated and elaborate devices but most of those commonly used were not. Perhaps the simplest of all was the Tail Pistol No. 58 Mk I used on both the Grand Slam and Tallboy bombs. The reason for this was that in operating in such a simple, mechanical, way it was very unlikely to malfunction (essentially the heavy striker had only to bend a piece of cross shaped brass on impact). The bombs to which it was fitted were neither plentiful, nor cheap, and duds were extremely undesirable.

Cheers

Steve

I not familiar with British WW2 fuses, but I an with USA WW2 fuses, because we were still using them when I was in USAF munitions in the 60's.
Most of the fuses we used at NKP were of the quick arming , not instant arming, medium delay type for low altitude use.

I see no logic in using a quick arming fuse for a bomb dropped from high altitude, though I can see that a bomb dropped from high altitude needs no delay, except a very long delay in some to hinder recovery efforts .

I suppose the logic in using a quick arming fuse is that's it's mechanically simple, the less there is to that could go wrong, the less that will go wrong. Also cheaper to make.
Most fuses are little mechanical marvels, when you using them by the millions, economics have to come into play.

tyrodtom said:

I suppose the logic in using a quick arming fuse is that's it's mechanically simple, the less there is to that could go wrong, the less that will go wrong. Also cheaper to make.
Most fuses are little mechanical marvels, when you using them by the millions, economics have to come into play.

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I think you have hit the nail on the head.

Some more complicated and expensive fuses/pistols were used. Nos 53 and 53A (no chance of a mix up then) gave a 30 or 60 minute delay. The No.37 Mk V could be set for delays from 6 to 144 hours by a combination of acetone (in a breakable ampoule) and celluloid discs and included an anti-removal device. Although I suspect you know exactly what the various parts I have mentioned are, a description of this device would fill a couple of pages. It was complicated and expensive and, unsurprisingly, rarely used.
A good example of the cost versus effect of a device is provided by the No. 845 Anti-Disturbance Nose Fuse. When fully armed this electrically initiated device would trigger an instant detonation on even a slight movement of the bomb. It was abandoned in 1943, manufacturing costs were high as it was a complicated device, and since the Germans had a similar device of their own they understood that freezing the fuse would temporarily cut off the electrical supply rendering it temporarily ineffective. The problem was handling it quickly before it warmed up !

The British did use some barometric fuses (Nos. 860 and 896 nose and Nos. 867,885 and 886 tail were common examples) but mainly in flares, target indicators, and other pyrotechnics for marking.

Cheers

Steve

The British anti-disturbance fuse you're describing sounds a lot like the fuse the US was still using during the 60's, seems like I can remember from school that it was developed by the British, and we adopted it. But that school was 50 years ago.

How to disarm it was classified above our clearance and need to know while we was in school, but EOD was in on it's method of safe removal. I figured out on my own it probably involved extreme cold.

There was a bad accident with a anti-disturbance fuse at Cam Ranh Bay. A fire( sabotage) on the flight line threatened a whole line of aircraft. A flight line crew member tried to remove the fuses from the bombs to make them less likely to explode if the fire spread.

If it was armed it would be sensitive to any movement, but the system was quite complicated. It was only after the arming vanes had wound out and the arming spindle broken off that the sequence, which included a 20 second delay to allow the bomb to come to rest, could completed. The bomb had to hit something hard enough to cause the relevant parts to be driven forward (essentially an inertia ring, held back by a spring, this was a nose fuse) to initiate the arming sequence. After this, the firing circuit would be completed, except for a mercury tilt switch. Any subsequent movement of the bomb would cause the mercury to move, completing the circuit.

Unfortunately accidents are always possible, and one or two British fuses were unpopular with the armourers who evidently thought they were a bit dodgy and potentially dangerous.

Cheers

Steve

Best way I know to defuse any bomb is hit it with a bigger one! EOD would not be a good career choice for me of that I am certain. My hat is off to those that can. Me I prefer to read about it.

Not just movement of the bomb could set the fuse off, but any movement of the fuse itself, like unscrewing it.
But the bomb would have to be armed for the anti-tampering devices to work , you'd think.

But the fuse had a red tag that went on it, that warned that once installed it was not to be unscrewed. The tag was removed before flight.

But it would be hard to determine exactly what happened at Cam Rahn Bay, everyone who was close enough to witness the events, died in the explosions
.
They did know there wasn't enough time or people available to start the aircraft and move them, or to remove the bombs, but they could defuse the bombs. The detonating explosives in any fuse are a lot more sensitive to high temperatures than the explosives in the bomb itself.

tyrodtom said:

Not just movement of the bomb could set the fuse off, but any movement of the fuse itself, like unscrewing it.
But the bomb would have to be armed for the anti-tampering devices to work , you'd think.

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Yes indeed. Very often a bomb, once uncovered, would be rolled or otherwise moved in an effort to access the fuses/pistols....with fatal consequences. If the fuse was readily accessible, then any attempt to remove it would have the same consequences.

Cheers

Steve

Zipper730 said:

WWII Mentality / Post-War Mentalities on Area Bombing

Public Relations on USAAS Bomber Usage: Mitchell Era
The general focus was on the use of bombers as defensive, against attacking ships. Essentially, the idea was that large bombers would be able to accurately hit ships at altitude beyond effective range of defensive guns and sink them effectively.

Official Plan for USAAS Bomber Usage: Mitchell Era
Mitchell had been far more forthcoming with the USAAS than the public, and had officially stated during his time in uniform that the plans would be for the intended Air Force to consist of around 50% fighter aircraft, 50% bombers, with 50% of the bomber force aimed for strategic ends, and 50% for tactical goals.

It would appear that Mitchell didn't have a definite view of fighters early on, and even saw dive-bombers as useful for military ends as he saw them used in WWI.....

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I'm not 100% sure, but I believe that Mitchell was OK with bombing cities. Where he differed from Trenchard and Douhet is that he didn't think that the bomber would always get through, and that the number one priority for the air force was to destroy the enemy's air force.

The problem with the "bomber will always get through" theory was that it didnt mention how many didnt get back.

wuzak said:

I'm not 100% sure, but I believe that Mitchell was OK with bombing cities. Where he differed from Trenchard and Douhet is that he didn't think that the bomber would always get through, and that the number one priority for the air force was to destroy the enemy's air force.

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He was okay with it, but wasn't too open with expressing it at first except possibly to a few people in specific circumstances. Later on he became more open.

The idea of knocking out the air-force on the ground was highly desirable: In truth the bombers usually did often get through, but the issue was how many.

stona said:

Essentially, yes.
The automatic system actually flies the aircraft to the release point where it triggers the bomb distributor. I wrote that for this final part of the bomb run, once the sight has been locked onto the aiming point, the sight acts as little more than a timer, but it was an infinitely more complicated instrument than that.
As soon as a bombardier hits a manual release button/switch it does indeed activate the bomb distributor.

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So what circumstances were the manual mode used over the non manual auto-release?

We should not ignore the German Lofte 7D sight either. Like the Norden and SABS this was a tachometric sight and like the Norden was connected to a system which effectively allowed the sight to fly the aircraft automatically to the target and release the bombs. the SABS did not do this (nor did the Mk XIV), as simpler system called the Bombing Direction Indicator displayed necessary course corrections to the pilot on later versions, earlier ones required the bomb aimer to call out corrections to the pilot as seen in many old war films. The British even considered using some captured Lofte sights, but this provoked a near mutiny at Farnborough where the boffins were developing the British sights!

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Why not just use the Lotfe? Regardless, what advantages did SABS have over us?

Zipper730 said:

So what circumstances were the manual mode used over the non manual auto-release?
Why not just use the Lotfe? Regardless, what advantages did SABS have over us?

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When using the Norden to aim then the automatic mode would have been used, it was an integral part of the system.

Why not use a T-34, or an 88mm flak gun? Nobody had a monopoly on good ideas or equipment. The Mk XIV was as good as the Lotfe and the SABS was better. It's one thing incorporating some aspects of another device into your design but quite another reverse engineering it for mass production, particularly when you already have an equivalent device in development. I don't know how many intact and usable Lotfe sights fell into our hands, but I vaguely remember that the discussion was about fitting them to Blenheims, which might not have been a brilliant idea.

The SABS was statistically the most accurate bomb sight of the war, its why No. 617 (and 9) Squadrons used it to drop extremely large bombs onto extremely precise targets, like viaducts, V-1/V-2 sites and battle cruisers. No. 617 Squadron achieved an average radial error of 125 yards from 20,000 feet in the period February to March 1945. In the same period another 'precision' squadron, No. 9, using the Mk XIV achieved an average radial error error of 195 yards. This is the best comparison we have between the two British sights.
Comparisons are difficult, it is not just the sight that influences accuracy. In this period, visually, the USAAF was typically placing about 30% of bombs within 330 yards of the target, which is widely comparable to Bomber Command with its Mk XIV by day, but the skill of the bomb aimers/ bombardiers becomes an important factor.
No 617 Squadron was a specialist precision bombing unit, and who knows how many hours they spent over the practice ranges, honing their skills.

Cheers

Steve

stona said:

The SABS was statistically the most accurate bomb sight of the war, its why No. 617 (and 9) Squadrons used it to drop extremely large bombs onto extremely precise targets, like viaducts, V-1/V-2 sites and battle cruisers. No. 617 Squadron achieved an average radial error of 125 yards from 20,000 feet in the period February to March 1945.

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The issue is further complicated by the nature of "earthquake bombs" themselves. The RAF crippled the Tirpitz by hitting close but not the ship itself, not knowing this they made another raid which hit and sank it. The raid on the V3 site hit it when actually it was supposed to narrowly miss, more devastation is caused by the bomb exploding deep under the foundations, in any case the V3 site was wrecked. On a viaduct they didnt want to hit it, if the bomb struck a column it may well just explode above ground, exploding alongside but deep underground destroyed the bridge and its foundations. The bombing height was also a compromise between accuracy and the speed of the bomb, in theory the bomb should be supersonic or close to it for maximum penetration but the height needed for this affected accuracy.

pbehn said:

The bombing height was also a compromise between accuracy and the speed of the bomb, in theory the bomb should be supersonic or close to it for maximum penetration but the height needed for this affected accuracy.

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And the height at which a Lancaster could actually carry the bombs (especially the Grand Slam).