Patent ID: 7428800

Claim:
An underground shelter of the type having a front wall, a back wall, two opposing side walls, a bottom and a top defining a substantially rectangular box with an opening defined in the top, a flat lid adapted to cover the opening, a roller means for alternately rolling the lid to expose or close the open top, the improvement comprising: a. substantially, the entire top of the box defining an opening: b. the lid adapted to be substantially flush with the surrounding ground level in a closed position: and c. a roller means comprising: i. a track affixed to each of the side walls near the open top and parallel thereto, ii. at least one upper track roller disposed between the lid and each track, each upper track roller rollingly supporting the lid as it moves relative to the track, iii. a support means for supporting a leading edge of the lid as it slides over the surrounding ground level, the support means having: (1) at least one rail roller adjacent to the back wall disposed between the lid and the track, (2) a lower track roller attached to the lid near the trailing edge, the lower track roller engaging a lower track surface, (3) at least one rail affixed to the underside of the lid between the rail roller and the lid, each rail having a sloped section near the leading edge of the lid, whereby when the leading edge moves away from the back wall, the lid is displaced upwardly by operation of the sloped section against the rail roller, providing additional clearance for the lid as it passes over the ground surface.