The Alliance "Rolling Thunder" Class Dropship is not a complicated vessel, basically being a huge mobile cargo bay. The "Thud", as its crews came to nickname it, is a remarkably solid ship structurally, but mechanically tempermental, and with crew facilities that are almost an afterthought. Used during the Unification War as a near front line transport, they are equipped to carry everything from troops, to supplies, to armored vehicles. Armed with just enough offensive and defensive weaponry to ensure a higher survival rate, they came standard with a load-out comprised of a chin turret anti-personnel gatling gun, dorsal mounted anti-missile weapon, and defensive ejectors mounted at all four corners. The gimbaled, wing mounted thrust engines, helped give the craft some maneuverability in atmosphere but it takes a skilled pilot to fly the ship as it has the handling and aerodynamics of a brick. In space, the oversized main drives did make the ship quite fast however. After the war, the Alliance decommissioned the class. After being stripped of all weaponry, and any sensitive military equipment, any remaining vessels were then auctioned off to used ship yards & civilian concerns.
Since Firefly was canceled I've tried to satisfy my cravings for it by watching the DVDs and reading the fan-written stories. One such series of stories set in the Firefly universe involves a small ex-Alliance military transport. The story extract, above, pretty much describes the ship. The landing gear extrude from all four corners of the bottom of the main hull. The huge belly doors are nearly half the length of the main hull and swing out to the sides, affording some cover to operations which preclude the space needed to land. The airlock connector is a small hatch in the bottom center of the huge cargo bay door. To give another indication of the scale of the ship, the small inset door on the fuselage bottom-front is 9 feet tall. Like Serenity and the Granite Gorge, the wing-mounted engines rotate from horizontal to vertical during take-off and landing. The main engines are in back - The two vertical indentations flanking the outside of the mess-hall/ common area. During full burn, inner doors swing open to the sides. Beneath the cockpit is a ring where the gatling gun turret had been mounted. Above the starboard wing is where the anti-aircraft missile battery had been.