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A cutaway showing the M4 mine in cross-section.

The M1,M1A1 and M4 are circular steel cased U.S. anti-tank blast mines with a distinctive cross shaped pressure spider. The mine was used during the Second World War and a copy produced in Argentina was used during the Falklands War. Another copy is produced in China. designated the No.4 mine. Variants of the mine have also been deployed in Chad and Tunisia.

Downward pressure on the spider presses down on the head of the fuze, breaks a shear pin, and inverts a belleville spring, flipping the striker downwards into a stab sensitive detonator, triggering the mine. The M4 version of the mine has two secondary fuze wells so that anti-handling devices can be fitted.


  • M1 - the mine has two filler plugs on the top surface.
  • M1A1 - the mine has a single filler plug on the top surface.
  • M4 - as the M1A1 but with two secondary fuze wells, one on the side one in the bottom.


  • Weight: 4.9 kg
  • Explosive content: 2.75 kg of TNT
  • Height: 75 mm
  • Diameter: 204 mm
  • Operating pressure: 250 kg to 120 kg


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