# Fuse arming of Upkeep [bouncing bomb]



## Taffy 2 (Jun 16, 2021)

Hi All, A few years ago I did extensive research on the Dam Busters Raid [Chastise] this was for a presentation I was to do for my military historical society [Fremantle, Western Australia] I obtained all the facts and figures, but with one piece of information needed I drew a blank ! I sent off enquiries to the RAF association and even the Imperial war museum but alas no replies.

The enquiry was that in one of the many books which I read on the raid, one author stated that the bouncing bomb [Upkeep] was to be armed by a crew member just as they crossed the Dutch coast. This as was pointed out was said to a precautionary measure taking into consideration that the bomb fuses [3] were hydrostatic types and would detonate the device when the correct depth of water was attained [30 feet]
so if the Lancaster did come down in the channel the bomb would not explode.

The hydrostatic fuses had a cap covering the water cavity which would have to be removed to arm the bomb, but if you take into consideration the position on the under belly of the plane the bomb being held firm between the release calipers, I fail to see how they could be armed while in flight ? . Another author states that the ground crew would remove the safety caps from the bomb before the Lancaster's left RAF Scampton .
So as you see a conflict of opinion, It's a small point but has bugged me for years. So if anyone can say which if any of the above is correct I would be grateful. Cheers

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## cvairwerks (Jun 16, 2021)

From looking at various designs of hydrostatic pistols for mines, there were probably two external safeties on the bombs. The first protected the pistol installation and was removed after the bomb was loaded. The second would have been removed just prior to the drop. The second safety would have been removed by a lanyard, which would release the plunger that was driven by the water pressure. With the second safety, it was most likely decided to be pulled by the bombardier due to the forces required.

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## FowellBox (Jun 16, 2021)

The last surviving bomb aimer from the dam busters squadron is *George Leonard "Johnny" Johnson*, MBE, DFM. I don't know if he will know or how to contact him, probably through the 617 squadron association.
Brian


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## Snautzer01 (Jun 16, 2021)

cvairwerks said:


> From looking at various designs of hydrostatic pistols for mines, there were probably two external safeties on the bombs. The first protected the pistol installation and was removed after the bomb was loaded. The second would have been removed just prior to the drop. The second safety would have been removed by a lanyard, which would release the plunger that was driven by the water pressure. With the second safety, it was most likely decided to be pulled by the bombardier due to the forces required.


Whats with the dislike the the o.p. ? Fat fingers?


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## cvairwerks (Jun 16, 2021)

Snautzer01 said:


> Whats with the dislike the the o.p. ? Fat fingers?



Looks like stupid iphone tricks are happening. I will probably quit trying to post anything during my down time here at work and wait til I get home in the mornings. I’ve noticed some other flakey things going on with this phone, but this is becoming a pain.

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## Snautzer01 (Jun 16, 2021)

Thought as much. I noticed it and found it a bit weird.


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## SaparotRob (Jun 16, 2021)

I've noticed a couple of accidental dislikes myself. I think I corrected them all. I thought it was just "Fat Finger Syndrome".


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## cvairwerks (Jun 16, 2021)

I’m going to have to review things this morning when I’m home on a desktop. Looks like there are a number of threads my phone has attacked!


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## Airframes (Jun 16, 2021)

I'd need to find the publication where I saw this, to confirm, but as far as I know, the mine was armed by a crew member, probably the Navigator or Flight Engineer,
A wire ran from the starboard side of the cockpit, externally, roughly in line with the Nav compartment. This was pulled to arm the weapon.
I'll try to find the book, which has photos (of the wire) and a description. It's in a Wing Leader Magazine issue, and I would guess is also covered in their dedicated book on the "Dam Busters".

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## Crimea_River (Jun 16, 2021)

From British military engineering at its best: The Bouncing Bomb - EngineeringClicks

The diagram sows provision for the fusing lanyard.

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## Crimea_River (Jun 16, 2021)

Looking at the diagram again, it would appear possible that the fuse was tripped when the trusses opened up with the lanyard attached but it could also be run to the crew stations. The sketch is not definitive.


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## Airframes (Jun 16, 2021)

I had the Wing Leader magazine issue, showing the lanyard /cable from the cockpit, saved in my "Favourites" lists, but it's now showing "Error 404" !!


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## Airframes (Jun 16, 2021)

The photo I was looking for was a good, clear close-up. The photo below is a different shot, cropped from an image of the entire aircraft, and the yellow arrow is indicating the "white line" which is the cable curving from the cockpit, to a pulley lower down the fuselage, and thence onto the arming pulley and pin.

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## Crimea_River (Jun 16, 2021)

Good stuff Terry.


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## Taffy 2 (Jun 16, 2021)

Thanks for that very informative response, I was aware that there was a lanyard attached to the calipers and that this was activated when released which in turn would set in motion the self destruct fuse pistol at the center of the bomb this was set for a 90 second delay just in case the the hydrostatic fuses failed, Barnes Wallis was taking no chances when he insisted that 3 fuses be installed. With that information that you all have sent I can now agree with the fact that a crew member would arm Upkeep from within the aircraft.
With my research I came across so many astonishing facts, the one which amazed me was that, 10 minutes from the target [Dam] the bomb was cranked up to spin at 500 rpm, It's hard to imagine four and a half tons spinning and then to have to hold the Lancaster steady at 60 feet for the run in. you have to take your hats off to them. Cheers and thanks again.

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## herman1rg (Jun 17, 2021)

Bacon awarded to Terry


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## cvairwerks (Jun 17, 2021)

I’d bet that the 10 minute point was required to get the bomb up to and stable at 500 rpm’s and give the aircraft time to resettle and stabilize from the gyroscopic influences of the bomb. A 4.5 ton gyro is going to impart a lot of force that would need to be counteracted until things were stable. Now days, we would program in a set stability offsets based on bomb rpm and let the flight control software deal with it.

From a flight test perspective, it would have been quite interesting to see the first inflight spin up tests.

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## KSJ (Jun 21, 2021)

My late father, (who always watched 'The Dambusters' movie) served with 617. The Bomb rotated clockwise toward the rear of the aircraft. The greatest loss of stability was the start of the rotation, hence the run up which allowed the aircraft, as CVAIRWERKS rightly observed, time to settle. The effect was the aircraft would drop as the mass started its spin, which at 60 feet was not a lot of room, so the start-up was tried several ways; with the bomb rotating slowly initially so there was a lower inertial mass effect and also with it rotating all the way through the flight, then only coming up to 500rpm on the approach to target, but most methods put greater loading and strain on the components, particularly the motor, which was difficult to control and regulate the speed. In the end, the 10 minute run in was decided as best to allow adjustments. The aircraft did not fly at drop height all the way , but it was also suggested, to give clearance over trees, to pick a spot over fields to start the bomb, (seriously!) then allow the aircraft to stablise and drop back down to 60ft for run-in. The greatest danger was turning with the bomb spinning, the gyro effect was a real problem and only flying straight and level was the safest. It is certain a couple of aircraft, certainly P-Popsy which overshot and tried to turn out from the hills surrounding the dam, were caught out by this. Also the loss of engine power suddenly, such as knocked out by AA fire, would, at 60 feet, be a disaster, because again the gyro effect would temporarily cause loss of control of the aircraft. You have to remember that Wallis experimented and did most of his research with a spherical bomb initially, then moved to a shape resembling a edam cheese, with rounded edges. It was the cost of reinforcing the bomb led to reverting to a cylinder shape which was easier to assemble and install without special trusses to facilitate launch.

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## Spitfire Steve (Jun 21, 2021)

FowellBox said:


> The last surviving bomb aimer from the dam busters squadron is *George Leonard "Johnny" Johnson*, MBE, DFM. I don't know if he will know or how to contact him, probably through the 617 squadron association.
> Brian


I will see what I can do with this. I'm friends with Johnny, but I know he's not been well lately (Well he is 99 years young) also in a care home. It may take a while to get an answer but I hope he will remember the sequence of arming.

This is Johnny when I took him out for lunch a few years back








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