  We present gauge theories in 2+1 and 4+1 dimensions with 16 supersymmetries
which are invariant under rotations and translations but not boosts. The
on-shell conditions reduce the dynamics to motion on a moduli space of BPS
states graded by a topologically conserved quantity. On each component of the
moduli space only half the supersymmetry is realised. We argue that these
theories describe M2-branes and M5-branes which have been infinitely boosted so
that their worldvolume `time' has become null.
