Polymer networks and gels are important classes of materials for defense applications. In an effort to improve the mechanical performance of these materials, we have investigated an approach based on double networks. A new potential method for forming double networks in a single step was identified from coarse-grained molecular dynamics simulations of polymer solvents bearing rigid side chains dissolved in a polymer network. Coarse-grained molecular dynamics simulations also explored the mechanical behavior of traditional double networks and indicated that the elastic modulus and molecular-scale fracture toughness of double networks depend on cross-linked density, the ratio of the highly to loosely cross-linked network, and the network interactions. Several new computation tools were also developed to more accurately describe model polymer networks. Epoxy single network gels were prepared, and it was demonstrated that the length and stiffness of the epoxy precursor can have a profound impact on the final network structure and mechanical behavior. An epoxy-acrylate double network was prepared, and preliminary mechanical evaluation suggested significant improvement in the toughness of the double network over the single network.