A third and rare type of encirclement can ensue from a breakthrough in an area of the enemy front, and exploiting that with mobile forces, diverging in two or more directions behind the enemy line. Full encirclement rarely follows, but the threat of it severely hampers the defender's options. This type of attack pattern is centerpiece to blitzkrieg operations. Because of the extreme difficulty of this operation, it cannot be executed unless the offensive force has a vast superiority, either in technology, organization, or sheer numbers. The Barbarossa campaign of 1941 saw some examples.