Nice work! The tone of the story was laid down incredibly, just like your previous entry. You're very good at that. I loved what the story insinuates, it reminds me of the "moment of change" that can be found in 5 minute short films.
There are some places where the illusion of someone writing a letter falls flat, such as the scene where he's writing about the defense gun thuds. It damaged my immersion into the story, but quickly recovered.
All in all, I only have high praise. I continue to look forward to your next work!