  The kinematics of stars in OB associations can provide insights into their
formation, dynamical evolution, and eventual fate. The low-mass stellar content
of OB associations are sufficiently numerous as to provide a detailed sampling
of their kinematic properties, however spectroscopy is required to confirm the
youth of individual stars and to get 3D kinematics. In this paper we present
and analyse results from a large spectroscopic survey of Vela OB2 conducted
using 2dF/HERMES on the AAT. This spectroscopy is used to confirm the youth of
candidate young stars and determine radial velocities, which are combined with
proper motions and parallaxes from Gaia to measure 3-dimensional positions and
velocities. We identify multiple separate kinematic groups in the region, for
which we measure velocity dispersions and infer their virial states. We measure
expansion rates for all these groups and find strong evidence for anisotropic
expansion in the Vela OB2 association of at least 11$\sigma$ significance in
all three dimensions, as well as some evidence for expansion in the $\gamma$
Vel and P Puppis clusters. We trace back the motions of these groups into the
past and find that the open cluster NGC 2547 is an interloper in the Vela OB2
region and actually formed $>$100 pc away from the association. We conclude
that Vela OB2 must have formed with considerable spatial and kinematic
substructure over a timescale of $\sim$10 Myr, with clear temporal substructure
within the association, but no clear evidence for an age gradient.
