In the 1960's NATO sought to make its air forces immune to surprise strikes by deploying aircraft able to take-off and land vertically from small landing sites hidden in the countryside. Developing the aircraft for this strategy proved quite difficult and only the British Harrier actually saw air force service.

The West Gernan Dornier Do 31 was designed, built and tested as a transport aircraft to support this strategy. It did work, but was found to be too expensive and to lack range and payload, so it never entered service. To this days, it remains the only VTOL jet transport aircraft ever built.

Wikipedia has more information about the original.

This model is shown in flying configuration. The Do 31 is also available on the ground, landing gear down, rear ramp open.