Misnay–Schardin effect

Unlike the blast from a rounded explosive charge, which expands in all directions, the blast produced by an explosive sheet expands primarily perpendicular to its plane, in both directions.

However, if one side is backed by a heavy or fixed mass, most of the blast (i.e. most of the rapidly expanding gas and its kinetic energy) will be reflected in the direction away from the mass.

[1][2] The Misnay–Schardin effect was studied and experimented with by explosive experts József Misnay (sometimes spelled Misznay incorrectly), a Hungarian, and Hubert Schardin, a German, who initially sought to develop a more effective antitank mine for Nazi Germany.

claim that World War II ended before their design became usable, but they and others continued their work.

[6] The later AT2 and M18 Claymore mines rely on this effect.