The M1 was a U.S. chemical landmine. It developed in 1939, and consisted of a one gallon (4.5 liter) gasoline can filled with 9.9 lbs (4.5 kg) of mustard gas agent. As issued, it had no bursting charge or fuze, but required a bursting charge of detonating cord to be attached via soldered tabs on the outside of the can.
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The original article can be found at M1 chemical mine and the edit history here.