"Beat! Beat! Drums!"

This particular poem by Walt Whitman stuck out for a variety of reasons. I really like historical poems and I love how he uses free verse in a way that grows. The entire poem has a certain fluidity to it even  though it seems a bit unconventional at times for a poem. The usage of "beat! beat! drums! --blow! bulges! blow!"is repeated three times in the poem and each time you read it, there is a kind of growing dread that is established. Between each of these verses, Whitman delves into the disruptive force of the war and how it is taking its toll on the citizens. With each new verse, the poem takes on a darker tone, so by the end of it when you hear the last "bulges blow" it leaves a lasting impression. I think this really worked to Whitman's advantage in this poem. It has a very dark tone that leaves that kind of foreboding feeling with the reader. So, does anyone else think that the repetition of the "beat! beat! drums!" meets that dark tone that Whitman is trying to establish? While reading, does the line get more powerful each time you repeat it to yourself?