Answer: C. The ship is the army, which is safe now that the war is over.
Step-by-step explanation:
Walt Whitman wrote this poem in order to commemorate the death of President Abraham Lincoln just as the Civil War was concluding and the Union had defeated the Confederacy.
The ship in this instance is the Union army that had returned from defeating the Southern armies and was now safe and sound. The Captain of the ship was Abraham Lincoln and even though the ship had returned, the captain had died.
It is one of the most famous poetic works in American history and one of the most loved.