 However, mines were poorly recorded and marked, often becoming as much a hazard to allies as enemies.Tripwire-operated mines were not defended by pressure mines; the Chinese were often able to disable them and reuse them against UN forces.Looking for more destructive mines, the Americans developed the Claymore, a directional fragmentation mine that hurls steel balls in a 60 degree arc at a lethal speed of 1,200 metres per second.