A Cray-2 supercomputer, installed at Lawrence Livermore National Laboratory (LLNL), California. Supercomputers are extremely powerful mainframe machines used for complex mathematical calculations demanding high speed & large storage areas. The Cray is used at LLNL for the mathematical modeling & simulations of the physics of lasers & nuclear explosions - the Nova laser system (a major project at LLNL) is currently dedicated to weapons physics research as part of the U.S. Strategic Defense Initiative (SDI - the Star Wars programme), in which space-based laser weapons are envisaged to play a leading role.