Upkeep mine [Bouncing bomb]

[jeffmorgan]

Hi All. I posted an inquiry last December regarding the arming of the Upkeep mine [Bouncing Bomb] I was trying to find out how the mines where armed, I understand now that the hydro-static fuses would have been set by ground crew, but the self destruct fuses according to author John Sweetman in his book "The Dambusters" would be set after crossing the Dutch coast and that would be carried out by one of the crew. This factor he points out was the reason why Squadron Leader Barlow's
Upkeep did not explode when his Lancaster crashed after hitting high tension electricity cables, they must have forgotten to arm the device? the bomb rolling clear and photographed and annualized by the Germans [ The best and most detailed drawing of Upkeep is in fact German]

The self destruct fuse which was fitted in the centre of the side plate of the mine [starboard] would start to count down it's 90 second delay when a lanyard was pulled by the action of the caliper arms that would swing outwards on release.

Now if this fuse was to be armed by a crew member and one looks at the position of the bomb which was slung underneath the Lancaster it would be be almost impossible to get at ! and the use of a lanyard says that it was purely a mechanical operation, and not electrical ?.

Personally I can not see the season of physically arming the self destruct fuse and would have thought that it would have been inert until the lanyard was pulled starting its destruction sequence?. I am not an explosive or fuse expert, I leave that up to you guys, I know that this is a small point, but I find it most conflicting when so many authors who have written on the subject either don't mention arming or differ in their interpretation.

I have written in the past to 617 and Dam Buster societies but have received no replies, so I turn to the experts.

I hope someone can help either from this site or links that i could be sent to. Thank you Jeff Lloyd. Western Australia.

 

[eodda]

Hi Jeff

I agree with you. The self-destruct fuze was a No. 42 Fuze modified in some unspecified way. Its method of operation is when, as you say, a lanyard is pulled on release of the bomb. The pull on the lanyard releases a striker which ignites a length of delay fuse. As with all British bomb fuzes and pistols (including the three main Mk. XIV Hydro-static Pistols on the Upkeep bomb) the fuze is connected to the aircraft via a lanyard which connects to an electo-mechanical fuzing unit. The unit is energised when the bomb is released live, or it is un-energised when the bomb is released safe (e.g. in an emergency). This either withdraws the final safety device in the fuze when the bomb is released live; the fuze then arms in the air, or it allows the bomb to be released safe with the safety device still in place. It is normal practice not to energise these fuzing units until the aircraft is near the target. This may explain why Sqn Ldr Barlow's bomb did not explode - the fuzing unit controlling the No 42 Fuze was not energised at the time the aircraft crashed.

My personal opinion is that the authors who have said that the No 42 Fuze was armed over the Dutch coast have misunderstood the meaning of the word 'armed' in this context. Fuzes aren't 'armed' until the bomb is released - otherwise they would be in a dangerous condition when the bomb is still on the aircraft. About the only bomb I've ever heard of being 'armed' while still on-board the aircraft was 'Little Boy' on its way to Horishima and that was particular circumstance. I think that in this case, they either mean that the fuzing units weren't energised until the aircraft were over enemy territory, or they've got their information wrong.

I hope that this helps

eodda

 

[jeffmorgan]

Thanks Eodda. That is by far the best information on the fusing of Upkeep that I have yet obtained. It is sad that when I have tried to obtain this information from whom I would have thought would be the experts on the subject, RAF association, 617 society, and even the Imperial War Museum London. they were either one liners saying don't know, or did just not reply? I have always been the type of person who likes to know what make things tick [ excuse the pun ] but again sadly these thing may have been forgotten.

Some of the interesting fact I did manage to come across during my research was things such as- The hydro-static fuses used in Upkeep were used for a season, they where the fuses used from the spigot launched depth charges that where fired from the side of warships
they had to withstand 4.6 tons of Upkeep hitting the water at over 200 MPH. The lanyard used was the same as a bicycle brake cable, the inner wire had to rotate inside its casing when Upkeep was spun up to 500 RPM, and the rev counter dial on the hydraulic motor used to calculate the speed of the spinning mine was the same type that was used a BSA motorbike, and the spinning sequence was stared 10 minutes from target [ 4.6 tons spinning at 500 RPM inside an aircraft, amazing !! ]

Thank you very much for your help. Jeff.

 

[beihan62]

Hi Jeff,I have been following this thread with interest,from what I see on the net the "Haynes Manual for the Lancaster"(yes true)has a cutaway diagram of the type 42 fuse used on the Upkeep Bomb,one mod,was to change the fuse from 30 sec delay to 90 sec,I also read that the bomb on Sqd Ldr Barlows Lancaster was still in the cradle in the wreckage when found by the Germans, so the self destruct fuse would not be armed as it was only armed when the cradle swung away from the bomb on release from the aircraft,

 

[beihan62]

Sorry Jeff,finger trouble,the cutaway diagram in the manual shows how the arming wire was attached to the type 42 fuse,
Hope this is useful,
Regards,
Don,

 

[jeffmorgan]

Thank you very much Don, that is interesting information regards the loss of Barlow's Lancaster with Upkeep still being held intact in side the cradle,

I,m keeping my fingers crossed at the possibility of there being a remake of the 1955 film " The Dambusters" I did read a year or two ago that Peter Jackson the director/producer of "Lord of the Rings" was very interested and that Steven Fry was to write the screen play. Also i do have a copy of the Hayes book entitled " Dam Busters Owners workshop manual" I'm not sure if that is the same as the one you are referring to. I shall check out the Hayes website

Again thank you, in fact thanks to all the people who have shown interest and the time to reply, this a very good forum. Cheers. Jeff.

 

[MindOverMatter]

Hi Jeff. My father flew Lancasters as a navigator with 101 Squadron and I have 3 bomb arming spools in my collection of Lancaster equipment. These hold the bomb arming wire which is attached to the pin which when pulled arms the bomb. I would assume a similar device was used on Upkeep.

I recently had a V.I.P. hangar tour of the Battle of Britain Memorial Flight courtesy of the flight commander whilst in the area attending a 70th anniversary event for the Nuremberg raid on 30th March 1944 which my father flew on. This gave me access to the Lancaster bomb bay and I got some good pictures of the bomb arming spool in situ. You can see that these don't have the steel wire fitted to the spool, possibly to save weight.

 

[MindOverMatter]

This shows a couple of bomb arming spools attached to bomb cradles. The winch that was used to load the bombs into the bomb bay is just behind.




This is one of my spools with the wire partially unwound and under spring loaded pressure to retract if I release the button under my forefinger. This would have been done electronically by a solenoid in the spool housing. The pin that arms the bomb, when pulled out, would be attached to the spiral clip just where the label is tied on.




These are various fuse types used in typical bombs carried by Lancasters. No type 42 unfortunately.




This is a brief run down on bomb arming and why it needs to be done at varying times. Bombs are normally carried in a "safe"condition fitted with a safety pin so that they will not detonate by default when released from a bomb rack or if they are otherwise ejected from the aircraft. The bomb arming spool ensures that any bomb unintentionally discharged will remain in a safe condition and also permits it to be intentionally discharged in a safe condition, such as when it is desired to jettison unarmed bombs prior to a landing.

Non-energized safe condition.​

The arming wire is stored in the bomb arming spool which is attached to the aircraft. In its normal non-energized safe condition the spool holds the wire under tension against the forces of gravity, acceleration and wind, but releases the wire from the spool at a tension insufficient to pull the pin and arm the bomb. The released wire then falls away still attached to the safety pin which remains in the bomb preventing it from detonating.

Energized armed condition.​

When electrically energized, however, the arming spool will lock so that the bomb is discharged in an armed condition. To actively arm it, a substantial pulling force on the safety pin by the arming wire is required to remove it. The arming wire is played out by the weight of the bomb as it falls away and the energy is stored in a clock type return spring within the spool. After the bomb is clear of the aircraft because the spool is set to lock it exerts a force on the wire pulling the safety pin out.The spring loaded wire then retracts back into the spool ready to be used again.

 

[jeffmorgan]

Thank you for that collection of photographs and the information, I think that i opened a can of worms when i posted my original request, I find this all fascinating. as usual the membership on this forum are so quick to help with any questions.

Cheers, and thanks to you all

Jeff.

 

[airman617]

Hi. Ive returned here after a long absence and can answer your query as I am currently writing a book on it. Basically the self destruct pistol (specially designed for Upkeep and Highball) was inserted into the mine and upon loading was 'armed', by which I mean the safety pin was removed so that it was able to fire. However, it was realised that should a mine fall off during take off the aircraft and half the base would be destroyed, and so a method of arming in the air was devised. A handle was fixed in the cockpit, attached to a cable which ran down the outside of the aircraft to the calliper arms and the hub that contained the fusing unit. When the handle was pulled (as they passed over the enemy coast) a 'claw was moved into position around the end of the SD pistol, effectively clamping it in position. When released the end of the pistol remained attached to the aircraft as the mine fell, starting the sequence.

 

[jeffmorgan]

Thank you "Airman617" that information is a revelation, I did read somewhere that there was a lever located at the side of the pilots seat, in which it stated that the pilot could release Upkeep in the case of an emergency ? but your information is far more detailed.

Good luck with your book, if you could let me have the title I shall keep an eye out for it. Thanks again. Jeff.