The speaker of this short poem imagines signing up for a war, but not in any heroic way. The title points to a toy, a tin soldier, and the poem seems to take that toy's point of view, or at least borrow its lightness. The speaker says they could join the war "glad as rust," a strange comparison. Rust is slow and quiet, something that spreads without effort, so the gladness here feels less like excitement and more like giving in to decay.
Then comes the surprising turn: the speaker would "be the enemy / for an afternoon." That makes war sound like a game of pretend, something a child might play on a rug, where someone has to take the losing side. The tone is casual, almost sleepy, yet there is something uneasy underneath. Treating war as a way to pass an afternoon is both playful and a little chilling. The mood is wry, quiet, and faintly sad.