Joe Haldeman wrote this novel as an answer to his experiences in the Vietnam war: War is stupid and inhuman, love survives. It is hard SF as its central idea is how war is elongated under relativistic speed where veterans return only after centuries
Let me begin with the deeply affecting love story aspect: The main protagonist Mandella’s has a relationship with another soldier. Heterosexuality will be a crime in the future and later on a strange perversity. But this Mandella is old-schooled and loves a woman of his original company. You might find it strange that a militaristic SF story contains a romance, but this one is perfectly believable and important, because they find each other to be the only connection to their known world. Everything around them changes fast, as they travel with relativistic speed – the story and the war starts with Vietnam veterans in the 1990s and ends in the 4th millenium. No wonder that culture, science, technique and language changes dramatically around them and they are estranged like the veterans coming home from the Vietnam war and find themselves surrounded with hippies.
In these thousands of years of war, we only see three battles – one short scene in space, one with Mandella as a privateer in a rushed battle without tactics and one as a military leader. As it sums up to only a fifth of that very short novel, other aspects are far more important. Like the boring routine to get to the brief battle full of terror. Like the love story or the cultural impacts when they return home in-between, e.g. the homophobic Mandella has to face his old mother becoming lesbian. Or the cynical impression we get of the government elongating the war because of economy reasons or turning everyone gay to control population.
I would like that everyone enjoying movies like „Ender’s Game“ would rather read this war deconstruction. It is a short and well-written page-turner deserving Hugo, Nebula and Locus Awards of 1975/6. And it is the first novel of the SF Masterworks series.