The present invention is directed to a system and a method for accurately locating a penetrating-type weapon within a shelter for detonation at a desired target site. The method includes reliably and accurately detecting thin layers of a shelter by use of a weapon frequency induced by a vibration in a portion of the weapon. The weapon frequency is detected and at least one harmonic frequency of the weapon frequency is analyzed to determine whether a deceleration threshold event has occurred. In one embodiment, the harmonic frequency may be compared to a target frequency which is associated with the deceleration of the weapon during penetration of a layer of media. In another embodiment multiple weapon frequencies may be detected, analyzed, or compared to detect the penetration of a layer of media.