  We address the issue of T-duality and U-duality symmetries in the
toroidally-compactified type IIA string. It is customary to take as a starting
point the dimensionally-reduced maximal supergravity theories, with certain
field strengths dualised such that the classical theory exhibits a global
$E_{n(n)}$ symmetry, where n=11-D in D dimensions. A discrete subgroup then
becomes the conjectured U-duality group. In dimensions D\le 6, these necessary
dualisations include NS-NS fields, whose potentials, rather than merely their
field strengths, appear explicitly in the couplings to the string worldsheet.
Thus the usually-stated U-duality symmetries act non-locally on the fundamental
fields of perturbative string theory. At least at the perturbative level, it
seems to be more appropriate to consider the symmetries of the versions of the
lower-dimensional supergravities in which no dualisations of NS-NS fields are
required, although dualisations of the R-R fields are permissible since these
couple to the string through their field strengths. Taking this viewpoint, the
usual T-duality groups survive unscathed, as one would hope since T-duality is
a perturbative symmetry, but the U-duality groups are modified in D\le 6.
