We analyze $M$ theory compactified on $\frac{(K3\mathrm{}\times S^1)}{Z_2}$ where the $Z_2$ changes the sign of the three-form gauge field, acts on $S^1$ as a parity transformation, and on $K3\mathrm{}$ as an involution with eight fixed points preserving SU(2) holonomy. At a generic point in the moduli space the resulting theory has as its low-energy limit $N=1\mathrm{}$ supergravity theory in six dimensions with eight vector, nine tensor, and 20 hypermultiplets. The gauge symmetry can be enhanced (e.g., to ${\mathrm{E}}_8$) at special points in the moduli space. At other special points in the moduli space tensionless strings appear in the theory.

• Received 28 February 1996

DOI:https://doi.org/10.1103/PhysRevD.53.R6725