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Luftmine B? The destruction of Chelsea Old Church 16 April 1941

Dear All,

I am an occasional user of BOCN, and I'm always on the same kind of mission. I am a historian, but with no expertise in ordnance, and this is where I come to double-check things. I am writing an article about an eighteenth century Quaker clockmaker from Chelsea - which is pretty far off topic for this site - except that a clock of his was in St Lukes Church, Chelsea. This was flattened in a raid on the night of 16/17 April 1941 ("the Wednesday"). Because I am a nerd, I like to get my facts straight. My research so far has led me to try to identify the explosive device that did all the damage - and I would really appreciate an informed opinion as to whether I am anywhere near right.

All the accounts describe the church being destroyed, and five out of six of the fire watchers being killed by the explosion of two mines. There are many versions of the account given by the surviving fire watcher, Arthur Mallet, but this one will do as well as any other - It landed with a thump, not very loud, ‘like a fifty pound weight falling on soft ground’. It was not an alarming noise, and he looked round casually to see what it was. Actually it must have been painted dark green, with the sea green parachute collapsing beside it. Mallett described it as a ‘big thing about seven feet long and as big as you could get your arms round.’

I have decided the most likely culprit was a 1000kg Luftmine B. If you agree with the first premise, I may have the suffix wrong - so a first check is to establish the right type of mine. Secondly, my current draft text is as follows:

"veryprobably a 1000kg Luftmine B, designed to explode at roof level, causingmaximum blast damage, but also fitted with an auxiliary timer, to trigger 25seconds later if it reached the ground."

Is this right? I find conflicting accounts about fuzing and time intervals when I look around. It wasn't just an impact device, was it? The bit about being designed to explode above ground to maximise damage sounds convincing, but with differences in all the descriptions I read I would appreciate some authoritative guidance, and perhaps some pointers to sources I can definitely trust. And the 25 second bit is important, in order to explain what happened. Mallett was next to a mine that had hit the ground. He would surely need 25 seconds to run far enough to escape with his life. The other five were caught out by a second mine which fell close both to the church tower and where they were running. I estimate 1000 tons of masonry collapsed as the tower imploded, down onto the street over the top of them. Is the fuze timing right? What fuze was fitted to these things?

Many thanks in advance for any advice you can offer to get me on the right track.

Kind regards,

James Nye
 
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I hope you get the answers James, I'll be watching this, as the lads no doubt will put their two penneth in. :top:

I look forward to the replies of this very sad but interesting episode.
 
Hi
(sorry for my poor English)

Luftminen ("Air mines") were in fact naval mines, designed against enemy shipping. They were dropped by Luftwaffe bombers into the sea, near harbors or passages or river estuaries etc. Their main fuze was magnetic or acoustic, activated by near passing ships. But the mine has also self-destruction system: when it fall into very shallow water (less than 2,5 meter - 8 ft deep) or on land, 20-30 second after landing it detonated.

The idea drop it against land targets was invented probably in the end of 1940 (1939?) by accident. When the planes dropped mines in harbors or near sea shore, sometimes some of them were moved by the wind and fall on cities or villages in neighborhood. The effects were surprisingly good (or rather bad :)). Slow falling mines can't penetrate into the ground or buildings, their thin-walled shells do not produced many fragments in moment of detonation, but air blast was enormous. In one case whole small village was almost completely ruined by a single mine - all of it's 20 or 50 houses were destroyed or damaged.

The German intelligence quickly find it out and Luftwaffe start to drop deliberately some mines against land targets. In each big air raid against British cities a small percentage of bombers dropped 500- and 1000-kg mines. At the beginning they used standard naval mines with parachutes and 20-second self-destruction fuze. Then they modified mines to the land-attack missions by removing magnetic/acoustic fuze and introducing typical contact fuze, instantaneous (non-delayed), activated by impact. Such mines could be dropped with or without parachutes. And then Germans introduced SB blast bomb series, extremely thin-walled (one of SB2500 versions was made even from aluminium) with extremely high explosive capacity, with instantaneous fuze, dropped mostly without parachute - and SBs also were sometimes called "mines".

There was probably no special fuze for midair detonation in the roof level. Barometric switch wouldn't be precise enough and radar proximity fuze in early 1940s wasn't invented yet. It would be probably possible to build a kind of electro-mechanical device with contact detector hanging on the long wire or chain under the bomb/mine, but I have no info about such device in German bombs or mines. For me most probably version is the roof-level detonations were caused by bombs/mines hitting the roofs of buildings.
 
Yep - spot on: sounds exactly like a 1000kg Luftmine B PM.

PS: You know there is an old book about the destruction of that particular church?
 
Thanks very much for these latest replies. I am indeed aware of the books on the church and have been through all the coverage of the raid I can find. It now seems clear what the mine type was, and that it simply had a delay action fuze. I am going to go with the 25 second figure I found for the delay - if Mallet was running for something like 20 seconds before the blast, I think that explains his escape. The rest of the firewatching crew were perhaps caught by the fact a second mine had landed closer to them, and the blast from the first triggered the second.

Many thanks again.

James
 
and ideally by reference to a specific fuze type for which the delay is clearly documented

According to the Mine Disposal Handbook, Part IV, German Underwater Ordnance of March 1, 1945, pp. 2-3 and 73-80, LMB used Z. 34 A or B mechanical bomb fuze, which detonaded the mine after 17 seconds from impact unless the mine was submerged to 15 ft or more.
A thread about the 34 B fuse can be found here: http://www.bocn.co.uk/vbforum/threads/22888-German-Ariel-Mine-Fuze(inert)-34B
 
Dear Grzesio, PERFECT! Exactly the detailed info I particularly wanted, down to page numbers. Many, many thanks.....

All the very best,

James
 
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