A new concept vehicle comprises six major components: Sedan body shell with back opening, Entity of movable roof, rear pillars, and liftable back window, Unit of foldable trunk top and tailgate, Rear side windows with glass panels, Auto track systems, and Affiliate parts. Based on a basic sedan body with rear trunk opening, the entity of movable roof, rear pillar and liftable back window moves backward or forward along the track systems, and the unit of foldable trunk top and tailgate that enclose the trunk and body back works together with rear side windows and other components to make two types of vehicle configurations of standard sedan and light SUV/station wagon (which concept can also be extended to application and configuration on a pickup truck).

A new concept vehicle comprises six major components: Sedan body shell with back opening, Entity of movable roof, rear pillars, and liftable back window, Unit of foldable trunk top and tailgate. Rear side widows with glass panels, Auto track systems, and Affiliate parts. Based on a basic sedan body with rear trunk opening, the entity of movable roof, rear pillar and liftable back window moves backward or forward along the track systems, and the unit of foldable trunk top and tailgate that enclose the trunk and body back works together with rear side windows and other components to make two types of vehicle configurations of standard sedan and light SUV/station wagon.

Method of functioning the retractable hard top system for convertible vehicles which implies splitting the ceiling in the middle (through the longitudinal axis of the vehicle), moving the rear window with the frame-like area around it on top of the trunk lid, opening the upper areas of the rear wings and folding compactly the remaining components of the roof inside the lateral areas of the trunk. This method significantly increases the usable volume of the luggage compartment and offers an easier access to the items carried in the trunk. Also, this method requires a less complex operation system which leads to less expensive manufacturing and maintenance costs.

Method of functioning the retractable hard top system for convertible vehicles which implies splitting the ceiling in the middle (through the longitudinal axis of the vehicle), moving the rear window with the frame-like area around it on top of the trunk lid, opening the upper areas of the rear wings and folding compactly the remaining components of the roof inside the lateral areas of the trunk. This method significantly increases the usable volume of the luggage compartment and offers an easier access to the items carried in the trunk. Also, this method requires a less complex operation system which leads to less expensive manufacturing and maintenance costs.

A military vehicle includes a cabin. The cabin includes a bottom assembly and a foldable top assembly. The bottom assembly is configured to receive and removably couple with different top assemblies. The foldable top assembly is configured to transition between a folded position for a low velocity aerial drop (LVAD) and a deployed position. The foldable top assembly includes a torsional spring configured to provide a torque to assist transitioning of the foldable top assembly from the folded position to the deployed position.