[en] GRACE is a five element arra of air Cherenkov light collectors designed to measure the energy of primary cosmic rays and operate on the terrain over the deep underground muon tracking detector. MACRO, at the Gran Sasso National Laboratory in Italy. The coincidence detection of air Cherenkov photons and deep underground muons produced in extensive air showers will allow an association of the primary energy with the muon events observed underground. We present detailed Monte Carlo calculations of the expected signal, a complete description of our detectors and test results of their initial deployment at the University of Michigan Peach Mountain Observatory. (orig.)