"Arms and the Boy" sounds an awful lot like it's going down at a World War I training camp. But where we actually are in the poem is less important than the larger context of World War I in general. That's the setting Owen was concerned with.
And what a setting it is. The sheer brutality of World War I was enough to set even the most violent of men reeling. After all, it was called the Great War and the War to End All Wars for a reason. Plus, the complicated politics in Europe at the time made it hard for soldiers to connect with the reasons they were fighting. For most, it seemed like sheer senselessness. The war hardly seemed about patriotism, or just causes. It just seemed like Hell on earth.
That's where this poem comes in. By giving the weapons minds of their own, Owen subtly points to the senselessness of the violence these soldiers experienced. It's as if men were killing each other simply because that's what their bayonets and bullets wanted them to do. It's a frightening prospect, that's for sure. But we can imagine that for the average soldier, it didn't feel too far out of the realm of possibility. After all, when you're out in the trenches, it can't be easy to remember and have faith in the decisions being made far away in the halls of power.