The title tells us the speaker is thinking about a casualty, someone harmed by war, but the poem never shows a battlefield. Instead it begins with an odd, quiet image: the war is "hard to fit into a silk coat." Silk suggests something smooth, delicate and civilized, and war is too large and rough to be wrapped in it. Any attempt to dress war up, or make it polite, fails.
The second stanza turns to people who "possess a cry / and never a body." It's a strange phrase. It may point to those who carry grief or horror that has no physical wound to show for it, or to voices that go on after the people behind them are gone. Either way, the pain exists but can't be pointed to.
The last stanza is the heaviest: some find it "burdensome / to continue to see." The speaker seems to feel exhaustion and a wish to look away. The mood is hushed, bleak and tired, as if witnessing itself has become a wound.