We're about to make an argument that might be controversial, so hold on to your butts—Moira Davidson may be the one true protagonist of On the Beach.
We can hear you guffawing from here, but just hear us out. Is Peter the protagonist? Well, no, not really, because he doesn't actually do much. What about Dwight? Well, we'd say the same thing, especially given the fact that Dwight is defined by his resistance to change. And lest you argue that Moira doesn't fit the bill because she isn't a part of Scorpion's mission, allow us to remind you that the mission served no function. It was useless.
Basically, Moira goes through more positive changes than any other character. As we watch her grow from a hard-partying young woman to a mature, old soul, we gain a healthy amount of respect for this rowdy gal.
When we first meet Moira, she's firmly entrenched in the Ke$ha stage of her life, which equals a lot of partying, drinking (double brandies, anyone?), and light-hearted romance. Sounds fun, sure, but it actually masks deep pain. As John points out, Moira's "trouble is that [she] won't face up to things" and "accept" that the world is about to end (2.226). These emotions eventually come to the surface when Moira meets Dwight and drunkenly confesses her pain, spurred on no doubt by the very real attraction she feels towards him.
In fact, she cares so much for Dwight that she begins to change. Dwight is an incredibly disciplined dude, which Moira admires, so she starts to discipline herself. She starts drinking less, trading her trademark double brandies for singles. She studies to become a secretary in a school where, ironically, "there are many more enrollments [...] than there were a few months ago"(5.126). She even goes to sleep before the break of dawn sometimes.
But don't think that Moira is doing this just to appease Dwight—she's turning over a new leaf for her own sake.
After all, Moira goes above and beyond the call of duty in her relationship with Dwight. She even convinces the prime minister to open trout season early for him—though the most powerful gesture she makes is getting a pogo stick custom-built for Dwight's daughter, who died during the war alongside the rest of his family. The fact that Moira not only accepts Dwight's belief that his family is still alive but encourages it shows how much she cares for him. Although they both know deep down that it's not true, Moira's willingness to get on Dwight's level shows her respect for his past.
Despite this personal growth (or maybe because of it), Moira isn't deterred by the realization that she and Dwight will never get together. As she herself says, a "half a loaf is better than no bread, when you're starving" (8.90).
Don't get it twisted, though—Dwight is crazy about Moira. How couldn't he be? In fact, he tries to kiss her one last time before their final goodbye—and she denies him, because if she let him kiss her, he wouldn't be the same man she fell in love with. Although it's a sad moment, we couldn't help but cheer a little because Moira is the one rejecting Dwight for once. And even when she chooses to end her life as close to Dwight as possible, she's doing it for herself, not for him.
That's a far cry from the wasted party girl who ended a first date in boozy tears. Even if we haven't convinced you that Moira is On the Beach's protagonist, however, we can at least agree that she grows into an awesome lady—one who deserves a longer life than the one she was given.