Death of a hero is the first theme to consider. It's obvious the narrator has great respect for the Captain, rendered by tones of compassion, reverence, and ceremony in the poem. "Exult, O shores, and ring, O bells!" exclaims the narrator, which shows the amount of esteem the Captain deserves. There are several ways the Captain (the hero) could be viewed; the more valid being Abraham Lincoln. In the actual book Leaves of Grass by Whitman, "O Captain! My Captain!" is headed under "President Lincoln's Burial Hymn.", and Whitman has written to Lincoln's memory before - for example, Abraham Lincoln by Whitman is featured in the Prose Forms: Journals section of The Norton Reader. This historical allusion in the poem contributes to the theme of Death of a hero, in which Lincoln is seen as the "father" of our country (symbolized by the ship) who has fallen dead, "bleeding drops of red."
Moving on to the sub-theme (if you will...) of family, The Captain could also be seen as the narrator's own father, with the ship symbolizing his deathbed. "Our fearful trip is done...the voyage closed and done," says the poem, signifying the trials and tribulations a family goes through. Whether the Captain represents Lincoln or the narrator's own father, the theme is applicable. Another stylistic technique demonstrating Death of a hero is apostrophe. Apostrophe is a style of personification in which the deceased or departed are spoken to as if they are still present: in the first stanza, the narrator calls out "O Captain! my