"Clash by Night" is a military science fiction short story by Henry Kuttner and C. L. Moore, writing under the pen-name Lawrence O'Donnell.
Cities are built in underwater domes known as "Keeps", while warfare is prosecuted under strict rules by surface ships and submarines crewed by mercenaries known as Free Companies.
The surface of Venus is uninhabitable due to the Sun's ultra-violet radiation, which leaves the mercenaries with dark skin tans compared to the pale Keep dwellers.
Scott, who is second in command to Commander-in-Chief "Cinc" Rhys, must muster his men and ships while dealing with the possibility of ending his career and living in a Keep, tempted by the hedonistic lifestyle, personified by a woman, Ilene Kane.
His dedication is further tested when, returning from negotiations with Mendez, commander of an allied Free Company, his boat wrecks and he must trek through the deadly Venusian jungle with a raw recruit who happens to be Ilene's brother, Norman.