Camoflet mines?

More usually spelled camouflet. A mine is a buried explosive device. Camouflet is a French word meaning 'crater'. A camouflet mine as used by anti-Nazi forces (e.g. in France) was a metal tube filled with explosive placed in a hole in the ground near a railway line, and triggered by the vibration of a train passing. The explosion would create a crater ("camouflet") and damage the railway track enough to derail the train.

thanks a lot indeed!