An armor structure for a vehicle underbody. The armor structure includes an inner plate that is mounted proximate to the vehicle underbody, the inner plate having a plurality of first openings; and an outer plate that is mounted distal to the vehicle underbody, the outer plate having a plurality of second openings. The inner plate and the outer plate are substantially parallel and separated by a spacing. The inner plate and the outer plate each have substantially equal V bends at an obtuse angle, and the V bends in the inner plate and the outer plate are aligned. The first openings and the second openings are (i) aligned across the spacing from each other, and (ii) substantially equal in area. When an underbody blast event is encountered by the vehicle, the outer plate is forced towards, and substantially against the inner plate such that there is no longer fluid communication through the first openings.