  UltraFast Outflows (UFO) are observed in some active galactic nuclei (AGN),
with blueshifted and highly ionised Fe-K absorption features. AGN typically
have a UV bright accretion flow, so UV line driving is an obvious candidate for
launching these winds. However this mechanism requires material with UV
opacity, in apparent conflict with the observed high ionisation state of the
wind. In this paper we synthesise the X-ray energy spectra resulting from
different lines of sight through a state of the art radiation hydrodynamics UV
line driven disc wind simulation. We demonstrate that there are some lines of
sight which only intercept highly ionised and fast outflowing material. The
cooler material required for the UV line driving acceleration is out of the
line of sight, close to the disc, shielded from the X-rays by a failed wind. We
fit these simulated wind spectra to data from the archetypal UFO source PG
1211+143 and show that they broadly reproduce the depth and velocity of the
iron absorption lines seen. This directly demonstrates that UV line driving is
a viable mechanism to launch even the fastest UFOs. We simulate
microcalorimeter observations of this wind and show that their high energy
resolution can resolve the detailed structure in the wind and recover the wind
energetics when combined with models which correctly estimate the line
formation radius of the wind. New data from microcalorimeters will pave the way
for physical predictions of AGN wind feedback in cosmological simulations.
