DARPA announces new X-plane programme

The aircraft, one of the rare formally designated X-planes, is meant to both hover and fly at high speeds with efficiency equal to dedicated platforms. Specifications call for an aircraft capable of more than 300kt (555km/h) maximum airspeed; higher than conventional helicopters can achieve, and the ability to hover with greater efficiency than current rotorcraft.

http://www.flightglobal.com/news/articles/darpa-announces-new-x-plane-programme-382691/