The Topfmines were a series of German circular minimum metal anti-tank blast mines that entered service with the German army in 1944, during the

Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

. The mines used a case made of compressed wood-pulp,

cardboard Cardboard is a generic term for heavy paper-based products. The construction can range from a thick paper known as paperboard to corrugated fiberboard which is made of multiple plies of material. Natural cardboards can range from grey to light b ...

and

tar Tar is a dark brown or black viscous liquid of hydrocarbons and free carbon, obtained from a wide variety of organic materials through destructive distillation. Tar can be produced from coal, wood, petroleum, or peat. "a dark brown or black bit ...

along with

glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...

plugs and components designed to be undetectable by

Allied An alliance is a relationship among people, groups, or states that have joined together for mutual benefit or to achieve some common purpose, whether or not explicit agreement has been worked out among them. Members of an alliance are called ...

mine detector Demining or mine clearance is the process of removing land mines from an area. In military operations, the object is to rapidly clear a path through a minefield, and this is often done with devices such as mine plows and blast waves. By contra ...

s. Often the only metallic part of the mines was the

detonator A detonator, frequently a blasting cap, is a device used to trigger an explosive device. Detonators can be chemically, mechanically, or electrically initiated, the last two being the most common. The commercial use of explosives uses electri ...

. To enable the mines to be found by friendly forces, the mines were painted with a black sandy substance called ' (

camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the ...

sand). Allied forces found that although the mines were undetectable by Allied mine detectors, German mine detectors could find the mines when they had been marked with Tarnsand.Specifically the Stuttgart 43 detector (TM 5-223) The secret of Tarnsand was maintained until after the end of the war, when it was discovered that it was a mildly

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consid ...

substance and the German mine detectors incorporated a simple

Geiger counter A Geiger counter (also known as a Geiger–Müller counter) is an electronic instrument used for detecting and measuring ionizing radiation. It is widely used in applications such as radiation dosimetry, radiological protection, experimental ph ...

Topfmine A

The Topfmine A had a flattened dome-shaped case with a raised flat circular pressure plate on the top surface surrounded by a circular shear groove. The case was normally made from pulped wood and cardboard mixed with tar for waterproofing. However, sometimes the case was made from

bituminous coal Bituminous coal, or black coal, is a type of coal containing a tar-like substance called bitumen or asphalt. Its coloration can be black or sometimes dark brown; often there are well-defined bands of bright and dull material within the seams. It ...

waste. The SF 1 fuze was inserted into the underside of the mine and was placed inside a large glass plug which sealed the bottom of the mine. A secondary fuze well was provided on the bottom of this plug for installing

anti-handling device An anti-handling device is an attachment to or an integral part of a landmine or other munition such as some fuze types found in general-purpose air-dropped bombs, cluster bombs and sea mines. It is designed to prevent tampering or disabling, o ...

s. The SF 1 fuze was constructed of glass and wood and contained a

and

booster charge {{unreferenced, date=August 2011 An explosive booster is a sensitive explosive charge that acts as a bridge between a (relatively weak) conventional detonator and a low-sensitivity (but typically high-energy) explosive such as TNT. By itself, the ...

. Pressure of approximately 330 pounds (150 kg) on the pressure plate caused the plate to shear off from the mine casing, collapsing down on the glass head of the pressure fuze. The glass head was driven downwards, crushing two glass vials of chemicals, which reacted together causing a flash, initiating the detonator, booster and finally the main charge of

TNT Trinitrotoluene (), more commonly known as TNT, more specifically 2,4,6-trinitrotoluene, and by its preferred IUPAC name 2-methyl-1,3,5-trinitrobenzene, is a chemical compound with the formula C6H2(NO2)3CH3. TNT is occasionally used as a reagen ...

. Two versions of the mine were produced - a fully waterproofed version designated "To.Mi.A4531" and the normal "To.Mi.4531".

Topfmine B

The Topfmine B (To.Mi.B4531) was broadly similar to the "A" version, the principal difference being a smooth case without a raised pressure plate. This version instead had an internal shear groove to prevent water from working its way into the mine and possibly deactivating it.

Topfmine C

The Topfmine C (To.Mi.C4531 or Pappmine) changed the design to an eight-sided flattened cylinder shape, with a central

fuze In military munitions, a fuze (sometimes fuse) is the part of the device that initiates function. In some applications, such as torpedoes, a fuze may be identified by function as the exploder. The relative complexity of even the earliest fuze d ...

plug on the top. This design was very thin-walled and

sympathetic detonation A sympathetic detonation (SD, or SYDET), also called flash over or secondary/secondaries (explosion), is a detonation, usually unintended, of an explosive charge by a nearby explosion. Definition A sympathetic detonation is caused by a shock wav ...

could occur if the mines were planted closer together than seven feet (2 m).

Specifications

Notes

References

* TM 5-223, Foreign Mine Warfare Equipment, November 1957
TM-E 30-451, ''Handbook of German Military Forces''

{{WWIIGermanMines Anti-tank mines World War II weapons of Germany Land mines of Germany Weapons and ammunition introduced in 1944