What metaphors are used in The Arsenal at Springfield by Henry Wadsworth Longfellow?

By saying that the collection of guns is like an organ, Longfellow is being metaphorical. He does not mean that one could play music on the guns as one could on an organ. However, his reference to the organ invokes a powerful image in the reader's mind. Although he has not stated so explicitly, the reader can infer from the organ reference that the arsenal's guns are all standing upright, arranged in rows with their barrels sticking up—like the pipes of an organ. This is the power of Longfellow's metaphor.