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Cameron knew that the success of the Scott film derived not from any single gimmick -- like the famous moment when the alien, nurtured unawares by John Hurt's character, pops bloodily out of his chest. Rather, the filmmaker, "using all the tools at his disposal," had created an atmosphere in which every shadow spooks and every sound alarms.
Since Alien had brilliantly exploited this limited form right up to its limits, "everyone said there was no upside to doing a sequel," Cameron says. "The logic was that if we turned out a hit, it was because Alien was a hit; if it was a flop, it was because we did it." He needed to find ways of cross-referencing to it, reminding viewers of a beloved source, which he managed in both small and large ways (they still serve corn bread on spaceships, and Aliens' voyagers do not like it any better than the Alien crew did). At the same time, Cameron and Hurd, who had by now become partners, had to find ways of bursting generic bonds.
At this point Cameron did his usual unusual thing. He went into hibernation with a stack of legal pads, denying himself all sensory stimulation except music he deemed appropriate to the project (Gustav Holst's The Planets). He believes in junk-food diets as an aid to inspiration, "provided you don't take it past four months." Four days, fortunately, was all the time it took him to work up a treatment for Aliens that typed out at about 45 single-space pages.
The first tactic, of course, was to open up the new film and populate it. Aside from the fact that combat-trained women are fully integrated into the group, the crew members are 20th century grunts unregenerately projected into the far future. Led by the usual by-the-books lieutenant who is incompetent and by the usual kick-ass sergeant who is supercompetent, their numbers naturally include Hudson (Bill Paxton), a coward, and Hicks (Michael Biehn), a quiet, steadfast type, who turns out to be the bravest of the lot.
They provide comic relief, especially Hudson, whose "Let's get out of here" response to every situation makes him a kind of audience surrogate. For Cameron, however, the Marines have another unstated use: "Their training and technology are inappropriate for the specifics, and that can be seen as analogous to the inability of superior American firepower to conquer the unseen enemy in Viet Nam: a lot of firepower and very little wisdom, and it didn't work."