This is the Fairchild XC-120 Packplane, a prototype cargo plane from the post-war era. The only one ever constructed, it was developed and built from a C-119 Flying Boxcar. It differed from the Boxcar by having a detachable cargo pod rather than an internal cargo bay. Below is a composite image of the pod being attached and the Packplane in flight.
The basic idea was to vastly decrease the time that an aircraft would have to spend on the ground loading or waiting to be loaded. Cargo pods would be preloaded by ground crews and taken to the planes and attached as soon as possible. The prototype was constructed by taking the fuselage of C-119B 48-330 and cutting it off just below the level of the flight deck. Then the landing gear were extensively modified. The wing mounted gear was extended towards the tail of the aircraft and two small wheels were added to the front of both to replace the nose landing gear that were now absent. The Packplane's four landing gear could be raised or lowered to facilitate the attachment of the cargo module, which had its own wheels. This was accomplished with a scissor-like frame, rather than hydraulics, as we might today. Below you can see the XC-120 in flight with no pod attached.
The XC-120 first flew on August 11, 1950. It was thoroughly tested and made the round of the airshows, but no orders were made and the project and the aircraft were eventually scrapped. If it had been accepted, production aircraft would have been designated the C-128. Designers planned a variety of wheeled pods for different types and amounts of cargo, some can be seen below and they are a little lacking in the streamlining area. I think it was an interesting concept and could have been useful. I also love twin boomed aircraft, they just look cool to me.
I would like to see the concept re-booted (maybe with a light turbine engine) as a multi-role aircraft. It could be outfitted with different mission pods like the Navy's LCS, albeit on a smaller scale. I could see a role for it as a light cargo lifter, transport, VIP transport, anti-submarine, or border/harbor patrol aircraft just for starters. Something like that could be advantageous, especially for smaller air forces that have many roles to fill with a small number of aircraft. How about a close air support bird with a targeting and weapons module? As nice as 12 or 13 forward firing .50 caliber machineguns sounds, that day is probably past us. But I could see a weapons module with targeting pods and side facing weapons like the gunships of the US Air Force being pretty useful. Perhaps heavy and/or large vehicles could be somehow slung and fitted with an aerodynamic fairing and carried, who knows?