Just a quick comment on the writeup from newmonster -- the steel from the elevated train line that e. e. cummings is referring to was largely sold as scrap to the Japanese, not made into American munitions. The train had been torn down to be replaced by a subway line, because the El was terribly noisy, and dripped oil and ash on the heads of pedestrians underneath. (See the Wikipedia entry for "IRT Sixth Avenue Line" for more details.) I do believe the message of the poem is anti-war; my impression is that it's about a young man who thought war would be glorious (rather than being, as the saying goes, days of boredom punctuated by minutes of horror), and it took dying to convince him otherwise.