Fan CastingThe Forever War

William Mandella is a physics student conscripted for an elite task force in the United Nations Exploratory Force being assembled for a war against the Taurans, an alien species discovered when they apparently attacked human colonists' ships. The UNEF ground troops are sent out for reconnaissance and revenge. The elite recruits have IQs of 150 and above, are highly educated, healthy, and fit. Training is grueling – first on Earth and later on a planet called "Charon" beyond Pluto (written before the discovery of the actual planetoid). Several of the recruits die during training due to the extreme environments and the use of live weapons. The new soldiers complete training and immediately depart for action via interconnected "collapsars" that allow ships to cover thousands of light-years in a split second. However, crucially, traveling to and from the collapsars at near-lightspeed has enormous relativistic time effects.