Mr. Roberts is a classic. Cagney, Fonda, Lemmon.
Master and Commander impressed me on its actual attempts to be as realistic as possible, and maintain O'Brien's intent.
Can we claim Top Gun as a maritime movie?
Despite the lower budget than Master and Commander, the Hornblower series did an excellent job.
Everyone else has already covered most everything I like.
But there are far more FAIL's in maritime movies than winners. Recently I saw The Guardian. Good acting, good theme, but the movie was so dang formulaic, I think 1 plot item surprised me...