Of all the early Bette Davis movies that I record from TCM, most of which feature her in very small roles, Waterloo Bridge caught my eye because it was directed by James Whale, best known for Gothic-style horror movies like Frankenstein, Bride of Frankenstein, The Invisible Man and The Old Dark House. Waterloo Bridge isn't a horror movie and isn't remotely Gothic, but it does feature Whale's tendency to portray social pariahs sympathetically. In this case that's Myra (Mae Clarke, who went on to play Victor Frankenstein's wife in Whale's Frankenstein), a prostitute in London during World War I. She starts out as a chorus girl (which totally sounds like an early Hollywood euphemism for "prostitute" already), but when work dries up, she's forced to become a streetwalker. Her favorite pick-up spot is the title location, where she meets Roy (Douglass Montgomery), the world's most naive and wholesome soldier. He too is American, fighting with the Canadian military because he just couldn't wait to join the war effort.
Myra agonizes over her relationship with Roy, who is clearly incredibly dim and can't figure out that he's fallen in love with a prostitute. Montgomery is bland and kind of dopey as Roy (which is sort of the point, I guess), but Clarke does a good job as the conflicted but good-hearted Myra, and Whale treats her position very matter-of-factly, as do the other characters who know about it. It's a refreshingly non-melodramatic portrayal of Hollywood's go-to tragic profession, right up until the very end when Myra gets what looks suspiciously like cosmic comeuppance for her harlotry. The pre-Code laxity also provides for a nice scene at the beginning in which Myra and her fellow chorus girls are in various states of undress backstage.
But what about Bette Davis? Yes, she's in this one, too, although to very little effect. She plays Roy's sister, who appears in maybe two or three scenes and exists solely for exposition purposes or to move the plot along. She's perfectly fine, but there's no indication of future star power, and the part could probably have been played by anyone. Davis would later get plenty of chances to play fallen women, and I think she could have done well as Myra here, although Clarke really does quite a good job, especially in contrast to Montgomery's tiresome swooning. Waterloo Bridge was based on a play, and it does seem a little stagebound at times; I think maybe half the movie takes place in Myra's one-room apartment. It was adapted again in 1940 with Vivien Leigh (the most famous version) and in 1956 as Gaby with Leslie Caron. Bette Davis never got the chance to play the lead.