Scaled Composites new X-plane takes to the skies

Scaled Composites new X-plane ...
The Model 401 on its maiden flight
The Model 401 on its maiden flight
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The Model 401 on its maiden flight
The Model 401 on its maiden flight

Scaled Composites Model 401 experimental plane has completed its maiden flight. The aircraft, which was developed in secret by the wholly owned Northrop Grumman subsidiary for an unnamed client, took to the air on Wednesday as part of a program to demonstrate the company's advanced, low-cost manufacturing techniques.

Details of the first flight are sketchy, though Scaled posted a video on Facebook showing the takeoff of Vehicle Number 1. The Model 401 prototypes have an identical outer design with a 38-ft (11.6 m) wingspan and identical performance characteristics. Lightweight construction allows for an empty weight of 4,000 lb (1,814 kg) and a takeoff weight of 8,000 lb (3,628 kg).

The Model 401 uses a single Pratt & Whitney JTD-15D-5D engine punching 3,045 lb of thrust. This provides for a speed of Mach 0.6 (456 mph, 735 km/h) and a service ceiling of 30,000 ft (10,000 m) with a flight endurance of three hours.

Two of the aircraft have been constructed. Vehicle Number 1 will continue its flight test program and expand the performance envelope before the second prototype's first flight.

Source: Scaled Composites

Somewhat unimpressive figures. What is the design brief for the use of this aircraft?
It has that decidedly "Browning 50 calibre" look of the somewhat smaller supersonic Bell X-1 and swept wings, not necessary for Mach 0.6. Interesting tail design too. I believe that airframe could make it close to Mach 1.5.
I wonder if the specified engine is the final one, or just an experimental engine intended to shake out the subsonic envelope?
Compressibility is not the only reason to use swept wings