Strings at the intermediate scale or is the Fermi scale dual to the Planck scale?

We show that if the string scale is identified with the intermediate scale, M_s=√M_WM_Planck ∼ 10¹¹ GeV, then the notorious hierarchy, M_W/M_Planck∼10^-16, can be explained using only M_c/M_s∼0.01∼α_GUT as small input parameters, where M_c is the compactification scale. This is possible for weakly-coupled Type-I open-string vacua if the observed world is assumed to live in an N=1 supersymmetric 3-brane sector coupled to a separate, hidden, 3-brane world which breaks supersymmetry, because for such a model M_W/M_Planck=1/2α_GUT²(M _c/M_s)⁶. We discuss some of the phenomenological issues presented by such an intermediate-scale string, showing that its benefits include: (i) the possibility of logarithmic gauge-coupling unification of the SM couplings at M_s; (ii) a natural axionic solution to the strong-CP problem with a phenomenologically-acceptable Peccei-Quinn scale; (iii) experimentally-interesting neutrino masses, and more.