This article examines sexuality in Ernest Hemingway’s novel The Sun Also Rises alongside warfare events and memories brought home from the frontline. This essay argues that witnessing the war firsthand and the unique circumstances from serving on the frontline has the potential to inspire homosexual tendencies among soldiers. This proposition can explain the veterans’ performances in the novel, such as Jake Barnes, Bill Gorton, Count Mippipopolous, and Harris Wilson. In varied places in this paper, the discussion depends on Menninger’s (1948), Fussell’s (2000, 2009, 2013), and Crouthamel’s (2008, 2014) accounts of the influence of modern wars on soldiers’ sexualities. As this current study shows, in an attempt to hide their newly-found homosexual tendencies, the veterans in The Sun Also Rises tend to over-assert their heterosexuality and avoid all nonveteran male environment(s). Reading the novel with Hemingway’s male characters’ performance of heterosexuality and avoidance leads to new ways of understanding the novel as the current paper discusses sexuality in the context of frontline memories and experiences.