A few months ago I came across a photo of what appeared to be a fairly modern looking Russian bomb fuze with this odd “Ball On A String” part. I did not think much of it at the time until I saw this picture of another Russian fuze with the same apparatus. Does anyone know anything about its function/purpose? Fuzes are incredibly interesting, some seem to be extremely high tech and beyond complicated. Does anyone have any info on the functioning of modern Russian fuzes?

I wonder if it has something to do with electronically “Setting” the fuze? Just a novice guess.



this ball-on-a-string is a pull-out wire, a feature that is commonly encountered on bomb fuzes.

As soon as the pilot disengages the bomb, the wire fixed to the aicraft’s pylon is pulled out of the fuze and this way initiates the arming process.

One question, could you provide detailed pictures of the stamped-in markings of this fuze please?

Many thanks in advance!

Thanks so much for your help, Chris! That thing was driving me crazy :-)


Hi guys,

Chris, i have to correct you. That is not a pull wire, but an electrical wire of the EPU pyropatrone which starts the pyrotechnical arming process. This is a standardized arming system for many type of fuzes. If you look carefully you will see the two contact surfaces and the isolation ring between them on the sphere at the end of the wire.


May I shed some more light on this.

This “cable” attached to the fuze (as on many other Russian bomb fuzes) is designated “EPU”. It has no mechanical function at all. As can be seen on the brown bakelite section on the ball shaped end this is a two pole contact with an electrical wire leading to the threaded bushing which is screwed into the bomb fuze. The bushing contains a squib which is nothing more than an actuator for the arming mechanizm of the fuze.
The moment the bomb is dropped the “EPU” is supplied with a certain currency and is arming the fuze (usually by applying gas pressure to some sort of safety slider, depending on the fuze mechanizm).

Mechanical “pull wire” arming systems look more simple.

oh, Vince was faster

Thanks guys! I have never seen this before and was so puzzled by it. You guys know your stuff big time!


Vince or EOD, Can you guys recommend a good web site or book or any good source of information I can see additional photos of this type of fuze system. Just real interesting stuff and I’d like to learn more. Fuzes really are a fascinating subject all to their own. This type is new to me, just happy you guys knew about it.


That’s the problem Jason, it is very hard to find something on modern Russian bomb fuzes. I assume several armies have such documents but doubt they will share them.

I guess that makes allot of sense for sure! It would be cool if their was a book on ordnance fuzes and their workings of all types. With GOBS of great pics!