Question

O Captain! my Captain! our fearful trip is done;

Answer 1

The author intended to create a bittersweet mood. Though the overseas trip has ended, and there is a happy crowd waiting for the ship to dock, the captain, who is the narrator's father, is dead. The vocabulary and phrases used, like exulting, the prize we sought is won, eager faces, etc, describe happiness. But phrases like cold and dead, pale and still, and mournful tread, describe death, making the poem's mood bittersweet.