XM41E1 gravel mine

[pzgr40]

Opened XM41E1 gravel mine. This mine was extensively used as a part of the McNamara line and as a fast deployable area deniel system in the Vietnam war. They were also used in search and rescue missions during the rescue of downed pilots by placing a rapidly depoyed minefield between own personel and the enemy. The Gravel mine can be found in several shapes and sizes. This type –the XM41E1- is 70x77mm square and it is ranked as an explosive type.
The small amount of charge in the AP models was considered adequate for injuring an enemy frequently wearing nothing more than sandals for footgear.
Some of the smaller types were used as an acoustic signal for air dropped microphones/sensors (ADSIDS sensors) which relayed their signal to a central control centre.

37 million gravel mines have been produced in 1967 and 1968, production seized in 1970. They come in the colours green, brown and tan. As the mine does not contain any metal parts it cannot be found with a metal detector.

The mine exists of an outer bag and an inner bag. The inner bag (C) is filled with a friction disc (E), 30 grams of coarse ground glass (D) and two pressed explosive pellets (F) existing of a mixture of 9,4 grams of Lead azide/RDX. As lead azide is very friction sensitive, stepping on the mine will rub the pellet over the friction disc with the ground glass between it. This will ignite and detonate the mixture.
To allow the mines to be transport safe and to be dropped from the air, the mines were stored soaked in freon 113 which acts as a desensetizer. Once released from their container/dispenser, the Freon would evaporate in between 3 and 8 minutes, thereby arming the mines. Some of the larger types used a two type tablet system that rendered the mine inert after a certain time, there is however no info about the reliability of this system. In time, the mine will slowly lose it’s function due to weathering. The Vietcong cleared the gravel mine fields using Oxen dragging logs.


A: Comlete gravel mine.

B : Outer bag.
C : Watertight inner bag.
D : 30 grams of coarse Ground glass.
E : Friction disc.
F : Explosive pellets.

The mines were typically deployed from SUU-41A/A dispensers, with 150 × XM41E1 per dispenser (10 dispensers per CBU), so a single bomb contained 1500 gravel mines, soaked in freon 113.
The bombs could be dropped from aircraft at between 600 and 6000 meters and at speeds of 370 km/h to 1300 km/h. The dispensers would burst at an altitude of between 200 to 300 meters, scattering the mines.

Other types of gravel mines are:
-XM22: 1/4 Circle , radius 64mm, explosive type containing 11,6 grams RDX/Lead Azide.
-XM27: 1/4 Circle , radius 83mm, explosive type containing 27,7 grams RDX/Lead Azid.
-XM40E5: Rectangle 45x32x10mm, illumination/warning , containing 0,54 grams of potassium chlorate/ phospor explosives.
-XM41: 1/4 Circle , radius 89mm, explosive type containing 16,3 grams RDX/Lead Azide.
-XM41E1 (the type described here) : Square 70x77mm, explosive type containing 9,4 grams RDX/Lead Azide.
-XM44: Square 25x25mm, T77 or XM114 Detonator, warning type.
-XM45E1: Square 45x32mm, explosive type containing 0,7grams RDX/Lead Azide.
-XM65: Square 76x70mm, explosive type containing 10,3grams RDX/Lead Azide.

An interesting piece of movie showing the effects of the gravel mine during a US test can be found here:
http://www.youtube.com/watch?v=QTWuzIL-Tlo
or search for : “Gravel Mine/Button mine, Anti-personel Mine 1967” on you tube

Main source of info :
http://www.airforcehistory.hq.af.mil/Publications/fulltext/fight_for_khe_sanh.pdf
Pages 94/95

Regards, DJH

 

[adammack]

How interesting. I had never heard of this type of mine before. Really very ingenious, and astoundingly simple! Thanks for sharing pzgr40!

 

[Speedy]

Very interesting movie! I have no idea that was possible to deploy Gravels by hand. How they achieve it? I think they use a kind of portable thermos flask with freon for carrying mines?

 

[weberoed]

The gravel mines were never employed by hand in combat. they were too sensitive once dried. I have a large folder on them and have been chasing info on them for years. There were 10 different models, different amounts of HE, some with shelf sterilization and some just rotted away in the jungle environment. They can, though not that often be found along the old Ho Chi Minh trail. There was also a pretty bad accident at one of the US Army Depot with them. manufacturing was interesting as they had to keep the azide/glass particles wet while being pout in pouches and sewing up.

 

[US-Subs]

Very interesting movie! I have no idea that was possible to deploy Gravels by hand. How they achieve it? I think they use a kind of portable thermos flask with freon for carrying mines?

The mines were loaded into plastic containers which were then filled with freon to reduce the sensitivity. The containers had their own fuze and bursting charge for dissemination. Containers were most often loaded vertically into a dispenser, when triggered the entire container was released as a unit. There was an indicator of the freon content on the container, if the level/pressure dropped to an unacceptable point it would go red and the container needed to be removed and destroyed.
I only have a shelf picture in the office, here is a cropped image to show the container.

 

[weberoed]

I have never found any hand emplaced unit information. That picture looks like one of the ADUs mines were in for deployment from a SUU. IF you have a doc on that please send it my way. My gravel folder is about 775 mb now

 

[Speedy]

US-Subs, weberoed - I know of course that Gravel mines were designed as aircraft weapon and dropped from cluster dispensers (SUU-41 for fighter planes, XM3 for helicopters, probably was also installation for C-123). As I say previously, I never ever think that was even possible to take it by hand - after the freon evaporated Gravel mines stay extremely sensitive. But in the youtube film pzgr40 linked I saw first time soldiers placed Gravel by hand; dropped it on the ground; buried it under thin layer of soil; made an improvised AT mine by placing Gravel on the small pile of C4. It was completely new for me.

 

[HAZORD]

Thank You Gentlemen for your comprehensive answers to my question! So in reality it was mine related, but not a mine itself.

I knew it was explosive related as it is marked inert in a number of places. It didn't make sense that it was a mine because of its huge size and odd shape. I always wondered how they kept the gravel mines sealed and wet before being laid.