  We investigate the effective theory of type IIA string theory on
six-dimensional orientifold backgrounds with SU(2)-structure. We focus on the
case of orientifolds with O6-planes, for which we compute the bosonic effective
action in the supergravity approximation. For a generic SU(2)-structure
background, we find that the low-energy effective theory is a gauged N=2
supergravity where moduli in both vector and hypermultiplets are charged. Since
all these supergravities descend from a corresponding N=4 background, their
scalar target space is always a quotient of a SU(1,1)/U(1) x
SO(6,n)/SO(6)xSO(n) coset, and is therefore also very constrained.
