The events of the sirens, planes, fire, and bombs create imagery and this gives us this idea of war and we can see it so clearly .It ties in with the subject of this poem as a whole.
The context of her saying she lost herself in the crowd relates back to the subject of this poem. So when it says she lost herself in the crowd, she could mean it literally, as in she lost in all the commotion, or metaphorically, as in she lost her identity and memory due to the chaos.