  The massless spectrum of the ten dimensional USp(32) type I string has an N=1
supergravity multiplet coupled to non-supersymmetric matter. This raises the
question of the consistency of the gravitino interactions. We resolve this
apparent puzzle by arguing for the existence of a local supersymmetry which is
non-linearly realised in the open sector. We determine the leading order low
energy effective Lagrangian. Similar results are expected to apply to lower
dimensional type I models where supergravity is coupled to non-supersymmetric
branes.
