  We present the results of a deep 300 ks Chandra HETG observation of the
highly variable narrow-line Seyfert Type 1 galaxy NGC 4051. The HETG spectrum
reveals 28 significant soft X-ray ionised lines in either emission or
absorption; primarily originating from H-like and He-like K-shell transitions
of O, Ne, Mg and Si (including higher order lines and strong forbidden emission
lines from O VII and Ne IX) plus high ionisation L-shell transitions from Fe
XVII to Fe XXII and lower ionisation inner-shell lines (e.g. O VI). Modelling
the data with XSTAR requires four distinct ionisation zones for the gas, all
outflowing with velocities < 1000 km/s. A selection of the strongest
emission/absorption lines appear to be resolved with FWHM of ~600 km/s. We also
present the results from a quasi-simultaneous 350 ks Suzaku observation of NGC
4051 where the XIS spectrum reveals strong evidence for blueshifted absorption
lines at ~6.8 and ~7.1 keV, consistent with previous findings. Modelling with
XSTAR suggests that this is the signature of a highly ionised, high velocity
outflow (log \xi ~ 4.1; v ~ -0.02c) which potentially may have a significant
effect on the host galaxy environment via feedback. Finally, we also
simultaneously model the broad-band 2008 XIS+HXD Suzaku data with archival
Suzaku data from 2005 when the source was observed to have entered an extended
period of low flux in an attempt to analyse the cause of the long-term spectral
variability. We find that we can account for this by allowing for large
variations in the normalisation of the intrinsic power-law component which may
be interpreted as being due to significant changes in the covering fraction of
a Compton-thick partial-coverer obscuring the central continuum emission.
