The airmen who dropped the bombs reported that the target structures stood undamaged by the detonation; "But then the crater collapsed, the ground shifted and the target collapsed". Later computer simulations reached the same conclusions; the significant part of the damage was done by generating a cavity in the ground, and that cavity collapsing in on itself causing the ground to shift and the target's foundation to shift or break causing catastrophic structural damage to the target supported by said foundation. The shifting ground caused any larger structure to become severely damaged, even if the bomb missed the target but created a crater near it.[3][4]